Apple grower pg 33-35

COVER CROPPING

Orchard ground should be cover-cropped prior to planting. Ideally, two or even three growing seasons are invested in building up the soil with the understanding that tillage access will never be as good once the trees get planted. Sod is turned the Wrst spring and planted to the Wrst of two buckwheat smother crops. Lime and rock phosphate are best incorporated at the start (if needed) to sweeten the microbial decomposition process. Interplant winter rye with hairy vetch in September to combine the nitrogen Wxation of a legume and the organic bulk of the rye root mass. Red clover interplanted with oats oVers a similar two-bit gain. Green manure options can include bulky Sudan grass, deep-rooted alfalfa, and Hardin soybeans. Choose what works best in your region to most ben-eWt your particular soil type. Most clovers and -alfalfa require a full year’s growth to get the maximum beneWt of added nitrogen.

A basic turf of -orchard grass and Dutch white clover can be established during the year of tree planting if no further row cropping is envisioned.

The cultivated orchards of our great-grandparents were put into a cover crop late in the summer to protect the soil over the winter and renew organic matter. The spring harrowing was essentially a “composting in place” that allowed for aerobic decomposition in the top several inches of disced earth. The fruit trees had no immediate competition during the peak of the growing season for soil nutrients or moisture. Additional cultivations after petal fall kept weeds from taking hold. The planting of a summer cover would be delayed in a dry year to reserve soil moisture for the sizing fruit. But not for too long. The growth of the cover crop helped check tree growth and thus hasten winter hardening.

I like the ideal of maximum soil preparation as much as anyone.

These immediate edges can be worked for a year or two while the trees are small. Annual -nitrogen-Wxers like Weld peas or soybeans lead into a later sowing of oats. Some tree feeder roots may initially get harrowed in the cover crop zone, but the gain in organic matter may justify the eVort. The in-row strip between trees grows to winter rye and self-seeded buckwheat, but wildXowers and other grasses eventually gain the stronger foothold. Any quackgrass that survives year one can be a nuisance around the gravel mulch base that surrounds the young trees, mandating hand-hoeing and/or Xame weeding. Gravity-fed irrigation lines ensure our young trees get enough moisture despite the surrounding growth.

Green manure crops should be incorporated into the soil while still green and succulent. Clovers can Wx up to 150 to 200 pounds of nitrogen per acre when properly managed. Grasses are better at increasing soil organic matter, primarily due to their high lignin content and Wbrous root systems.

Pathogenic fungi can be suppressed by disking in a green manure: the high nitrogen content results in rapid decomposition, which in turn stimulates germination of dormant spores of the pathogen. Since the trees are not yet planted, the germinated spores, having no food source, get attacked by other microbes. Annual legumes grown alongside the tree row should not be directly disked in green in late summer, as the release of nitrogen may delay hardening oV. Mow the legume crop to lie in place, wait a few days, then sow a grass-type cover into the dried green mulch. A biennial legume interspersed with a scattering of oats could be mowed but then left to grow through the fall for shallow incorporation the following spring. The nitrogen boost would come when needed, the winter-killed oats would improve tilth, and the now open ground could be left rough until the summer planting of the next protective cover.

Four Season Harvest, Eliot Coleman

Pgs 14-15

The Organic Garden

Let’s take a moment to discuss the benefits of organic gardening. No fearful tales are involved.I have no moral sermon. I have no plan to drown you in pages of factual data. Our home garden is organic, as it has been for thirty years, for a very practical reason. Organic methods are simpler and work better. That’s right, they work better. Chemical agriculture is one of the great myths of the 20th century. The chemical salespeople swear that chemical fertilizers and pesticides are indispensable. In our experience, they are totally superfluous. They are necessary only as a crutch for the weaknesses of industrial food production.

Basically, organic gardening means a partnership with nature.

Nature’s gardeners are numerous and eager to help. Millions of beneficial organisms (everything from bacteria to earthworms to ground beetles) thrive in a fertile soil, and they make things go right if the gardener encourages them. The gardener does that by understanding the natural processes of the soil and aiding them with compost. The inherent stability and resilience of natural systems can be on your side if you work with them. Organic gardening is a great adventure, an expedition into a deeper and more satisfying understanding of vegetable production. You are now a participant rather than a spectator. You share creation.

A delightful bonus of organic soil care is the quality of the vegetables.

We are convinced that future investigations will confirm the value of food quality, just as present research has already confirmed the essential place of vegetables in the diet.

Since the key to vegetable quality is the quality of the soil in which the vegetables are grown, you want to have good raw material for the roots of your plants to forage in. Soil quality is influenced by the practices of the gardener. For a soil to be truly alive and productive, it must contain plenty of organic matter, plus the full spectrum of minerals. The soil can then feed the vegetables. A vital, alive soil will produce vital, alive vegetables.

Growing Green: Animal Free Organic Techniques

By Jenny Hall & Iain Tolhurst

2.2 Soil structure and physical components

An optimum soil structure has been described as:

a water-stable, organically enriched, granular structure where all the water reserves

within aggregates can be fully exploited by root hairs and the space between aggregates

is large enough to allow rapid drainage, to admit air and to facilitate the deep

penetration of roots.

The mineral components of soil are derived from rocks, which are weathered

into all sorts of sizes from the largest boulders through to stones, sand, silt

and the tiniest particles of clay. Soils vary widely in their relative contents of

sand, silt and clay, but a good proportion is around 20% clay, 50% sand and

30% silt. Such mixtures are known as loams.

All soils need careful management, especially the timing of cultivations, which

should be carried out when the soil moisture content is just right – not too

wet and not too dry.

Sandy soil – is the easiest to work, warming quickly in spring and draining

easily. However, it tends to be slightly acidic and can dry out easily in the

summer. It has large pore spaces and, if the soil is not carefully managed, rapid

water movement through the sand will leach nutrients, leading to fertility

deficiencies. Also, the larger air spaces mean that organic matter is more likely to

be oxidised and lost. Sandy soils need organic matter to bind particles together.

Silty soil – is a fragile soil that can cap at the surface.The pores are small and

can remain completely waterlogged in wet conditions or can become dusty in

dry conditions.

Even if some form of structure with large air pores can be

achieved, it can disintegrate easily with a packing down effect leading to

compaction where the soil becomes airless. Silts benefit from the addition of

organic matter to open up pore spaces.

Clay soil – is late to warm in spring, heavy to work and has poor drainage. It

is sticky when wet and tends to bake hard in summer. As the soil is wetted

and dried the clay particles can expand and shrink, causing cracking. Clays

benefit from the addition of organic matter, which opens up the air pores and

makes the soil less dense.

The characteristic behaviour of clay particles is very different from that of sand

or silt.The latter are chemically inert and only affect water retention and

drainage. In contrast, clay particles, the smallest particles of rock, are

electrically charged and can attract, hold and make nutrients available to plants.

Peaty soil – is organic, as opposed to mineral, in origin.

An example of its

formation is when, millennia ago, seas flooded established forests and in recent

times such land has been reclaimed from the sea. Such soil can look and feel

just like compost or peat.These soils tend to be too acidic for earthworms.

They can also be boggy in places and need careful attention to drainage.

Organic matter – The average content of organic matter in arable land is

around 2%. A lower organic matter content will give rise to greater structural

stability and hence greater susceptibility to erosion. High organic matter levels

e.g. over 10% in non-peaty soils will generally indicate low levels of biological

activity.This may be due to acidic pH levels and / or poor drainage.

2.3 Recommended practice – adding plant-based compost to soil

Topsoil is a mixture of disintegrating mineral rock and organic matter.

Organic matter is material of once living origin: plant debris, manures and

dead bodies of all animals and microscopic creatures. Organic matter is

continually decaying, feeding the soil biota (billions of soil bacteria, fungi,

microscopic soil animals and larger animals like worms). Replenishing organic

matter lost through oxidation (accelerated by tillage) will improve soil

structure. Organic matter retains moisture, binds sands and opens up clay

soils, making all soils more easily worked. Earthworms are the most

significant species for soil structure, as their burrows provide air and drainage

channels. Earthworms require plenty of organic matter and do not like acidic

conditions, poor drainage or frequent tillage.

If you follow the guidelines for making good compost in chapter 4, then you

should be left with friable dark compost that crumbles in your hands and

smells pleasantly earthy.

Food Not Lawns: How to Turn Your Yard into a Garden and Your Neighborhood into a community

By H.C. Flores

Pgs24-27

Urban Ecology

Many people see ecological living as something they will do later, when they can finally afford a big place in the country, but I say, “Start now!” Even, or perhaps especially, if you live in a tiny apartment surrounded by a concrete jungle, you should always try to find simple ways to repair the earth, educate others, and prevent further destruction of the natural world.

Growing ecological gardens, wherever you can, is never a waste of time. Nothing lasts forever, and if you can get a few baskets of food without damaging the environment, and perhaps leave behind some long-living fruit trees, then the larger ecological community will surely benefit from your labors. If you can do these things while also educating others, then your work will succeed many times over.

In addition, not everyone wants to live in the country, and if everyone moves there it will all become the city. Many people plan to spend their lives in the city, happily, and have no plans to go rural.

This is good, because if we want to support the growing human population for more than another few centuries, we are going to have to grow up,not out. We also must ensure that urban communities can provide for their own needs, using resources from the local area. These needs include food, building materials, water, medicine, and much more, and currently there are no cities to provide a model.

We can, however, create our own models by simultaneously caring for the earth, caring for the people, and recycling resources. In these models rural food surpluses will supplement urban subsistence gardens, and the ecological integrity of each bioregion will depend upon how well the city dwellers can provide for themselves. Improving the ecological health of cities is crucial to achieving a healthy bioregional community, and if the ideas in this book inspire you, then begin doing these things now regardless of where you live or whether you rent or own your garden site. Do it for the land and to experience the personal transformation; consider the harvest a bonus, rather than the goal. The sooner and more fully we embrace an ecological ethic in our daily lives, the better our ability to place ourselves within the deep ecological context of our communities, and the clearer that context, the more accessible our vision of paradise.

Urban ecology is not so much a matter of “saving the earth” as it is a chance to improve the integrity of our own human lives and, thus, our chances of survival as a species on earth. The earth probably does not care whether we save her. She will most likely continue to turn and breed life long after humans have gone extinct. If we continue our current trend of wanton consumption and shameless waste, this may occur much sooner than later.

I know I sound like Chicken Little saying, “The sky is falling!” but if we don’t change our direction, we will get to where we’re going, which is currently extinct. This deep impermanence, while it may seem grim at first glance, is actually a blessing: Our own fragility gives us the impetus to act now to create healthy lives that harmonize with nature, and to know the comfort, joy, and inspiration brought on by an organic life. Why waste years and decades locked into jobs and consumer boxes that kill and oppress us when paradise is the alternative?

In my experience most people want to eat healthy food, care for the earth, and do otherthings that help create a better future for humans and other species, but they feel powerless against economic and social constraints.

This has a lotto do with the fact that millions of people don’t have a place to grow food, and the people who do have access to land, such as in rural and suburban areas, rarely steward it to the extent we need.

In addition to land, we also need tools, seeds, plants, and other materials, and most people can’t afford to just go out and buy it all. It is a common misconception that you need a lot of money to transform your home, garden, and community into paradise. But you can’t buy your way to a healthy ecology—you have to innovate it.

Integral to growing paradise gardens is recycling resources to do so. Every city in the world is rife with useful waste, and recycling it is an essential component of a healthy urban ecology. By understanding the flow of resources in the community around our gardens, we can better place those gardens within their deeper ecological and social context. Yes, growing organic food is always worth doing, but what of the truckloads of good organic produce that farmers and distributors throwaway? Using this waste for food and growing something else makes so much more sense.

Get acquainted with locally available, free resources—land, food, and otherwise. This is the first step in turning your yard into a garden and your neighborhood into a community, and recycling those resources is the next step. Focus on making best use of what is near you now, and buy new stuff only as the very last resort. The more we recycle the waste stream toward meeting our basic needs, the closer we come to closing the ecological loop.

Urban ecology is a big issue, and one that will take many years and many ideas to understand, but if we start with growing food where we can, we will be moving in the right direction. We can find space and resources that don’t cost money; we can build gardens and communities that make social and ecological sense.

This chapter will focus on making these resources more accessible. We will look at how to find a garden space if you don’t have one, and how to make the most out of the spaces you find. Then we will see how to tap into the flow of useful surplus that goes to waste every day, in every city in America, and how to divert that flow toward your garden and community.

Gardeners usually only sow seeds of garden varieties of flowers and vegetables. Most of these have been bred over the centuries to be quick and easy to germinate. It comes as a surprise to many people that, apart from these mainly annual plants, the seed of most species of plants in the wild does not germinate as freely and quickly as cress. In fact a large number of plants tend to use mechanisms to delay the germination of their seeds. There are many reasons for this but we will only look at those mechanisms for temperate plants. Although what comes next may seem complicated it is surprising how quickly you can pick it up, especially if you put yourself in the place of the seed and try to think what it needs in order to germinate.

The majority of plants ripen their seeds in late summer and early autumn when the weather is suitable for drying the seed. However, not many plants want their seed to germinate at that time of year since it would have to face the rigours of winter as a small vulnerable seedling. Therefore various strategies are employed to delay germination until the spring. These strategies include:

1. A hard seed coat that slowly breaks down overwinter and does not allow water to penetrate until late winter or spring (a seed cannot germinate until it has imbibed water).
2. An immature embryo that does not ripen for some months after the seed has fallen. Sometimes a period of warmth is also required and this can mean that the seed will not germinate until at least 2 winters have passed.
3. Various chemicals that can inhibit germination. These are gradually leached out of the seed by winter rains.
4. A sensitivity to cold. Some seeds require a period of cold weather in order for certain chemical changes to take place in the seed. Only after this cold spell can the seed germinate.

Seeds often employ more than one of these strategies which can complicate things no end. Some seeds have so many inhibitory mechanisms that they can take 4 years or more to germinate.

It is possible for the gardener just to sow the seed and sit back and wait for nature to take its course but, although this involves the least work it also has the greatest risks. The longer a seed is kept in a seedpot without germinating the more risk there is of the seed being lost either to insects, birds, mice, the gardener forgetting to water it in the summer and the seed desiccating and a whole host of other possible accidents. Plants produce thousands of seeds but only one seed during the entire lifetime of the parent plant has to come through to maturity in order to maintain the population, therefore in nature a huge loss is expected. Gardeners only get a few seeds and cannot afford to waste them. Therefore they look for ways to speed up the germination process. These methods will now be looked at in some detail.

Germinating Seeds

Sowing ‘green’ seed. If the seed of certain species is harvested before it has fully dried the seed coat will not have fully developed and certain chemical inhibitors may not as yet have been put in the seed.

By sowing the seed immediately it is harvested, usually in a cold frame or outdoors, germination can be expected in the spring. This can save a year or mores wait and entails very little extra effort so long as the seed comes from your own plants. The trick is in judging when to harvest the seed. The embryo must be fully developed or the seed will probably shrivel and die but if you leave it too long to harvest the seed will have developed the various inhibitors.

Scarification (or Scarify) A treatment for seeds with hard seed coats. Scarification is using one of several methods to reduce the seed coat before the seed is sown. These methods include:

1. Hot water treatment. Water is brought to the boil and then allowed to cool very slightly. A small amount of water is then poured onto the seed. It is stressed that the amount of water must be small. The idea is that the hot water will soften the seed coat, leach out certain chemicals that may be present and that can act as germination inhibitors and encourage the seed to imbibe. It is not intended to cook the seed! As a rough rule of thumb you put a thin layer of seed into a container and then just cover the seed with water, perhaps the depth of water should be twice the depth of the seed layer. This should then cool fairly rapidly. More hot water can be added a few minutes later, perhaps the same as the quantity that was first added. The container is kept in a warm place for 12 - 24 hours and the seed is then sown. This method is used principally on legumes but is also suitable for many other types of seed. With legumes in particular, you should notice a distinct increase in the size of the seed after it has been treated, some seeds do not swell up though. Especially with legumes it can pay to repeat the practice if the seed has not swollen.
2. Abrasion. Here the seed coat is reduced by literally filing it away with sandpaper or a file or any other method you might care to imagine. Fine with large seeds but rather fiddly with small ones. You must be very careful not to file right through the seed coat and into the seed, you must be especially careful not to damage the embryo since this will kill the seed before it even germinates. Sometimes you simply file one small area of the seed coat until you are almost through to the seed, at other times the whole seed coat is abraded. This can be done by putting the seed into a drum that has a rough inner lining (perhaps a lining of sandpaper) and than revolving the drum for a while until the seed is abraded. It is very easy to overdo it if you are not careful. Alternatively, with some seeds it is sufficient to pierce the seed coat with a needle in order to admit water. Once again care must be taken not to damage the embryo.
3. Acid treatment. Not one for the faint hearted, nor for most amateurs. It involves soaking the seed in sulphuric acid until the seed coat has been reduced, then neutralizing the acid and sowing the seed. Timing is crucial, if the seed is in the acid for too long it will be killed. I do not use this method so cannot give full details.
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Stratification. This can be of two kinds, warm or, more usually cold. Stratification is a way of convincing the seed that it has passed a winter or a summer and winter and that it should now germinate. The first thing to do is either sow the seed in moist compost or put it in a plastic bag with about 5 times its bulk of moist leaf-mould ( proportionally more leaf-mould if there is only a little seed and proportionally less if there is a lot of seed). Cold stratification involves keeping the seed in a cold place for a specified period. The salad compartment of a refrigerator or a shady north wall outdoors in winter can both work. A freezer is not recommended. The temperature for cold stratification is usually in the range of 2 to 5c, it should not normally be frozen. Warm stratification involves putting the seed in a warm place, perhaps an airing cupboard or a warm greenhouse for the time specified. It must be stressed that the seed has to be moistened before stratification and must not be allowed to dry out.

Soaking. Very similar to one of the methods of scarification but this time the water does not have to be so hot. This method is used mainly for legumes and is intended to speed up the germination rate by days rather than months. The seed should swell considerably when soaking and should start to germinate immediately. Especially helpful when sowing peas or beans in the outdoor garden.

Having learnt the various methods of inducing seed to germinate, how can you tell which method(s) to apply to the seed of any particular species? I’m afraid that there is no hard and fast rule. Considerable research has gone into the subject and there is a lot of literature available, though much of it is rather specialist and not easily available to the average grower. If the plant appears in our database then there is a very good chance that we will be able to tell you, but you can glean much for yourself if you know a little bit about the native habitat of the plant. One very simple rule of thumb for growing trees, shrubs and other perennials from areas with cold winters is that, if in doubt, sow the seed as soon as it is ripe and keep it in a cold frame or unheated greenhouse. Sometimes the seed will germinate quite quickly and you will have the problem of getting it through the winter without it going down to some fungal disease, but this is preferable to keeping a pot of seed for three years without germination ever taking place! If the plants you are trying to grow come from areas with milder winters (with only occasional frosts) then sowing the seed in a cold frame in late winter is usually more appropriate.

If the plants come from areas that experience no, or virtually no, frosts, then sowing the seed in mid spring is usually more appropriate. If the seed of any species that you obtain has a hard seedcoat, then it cannot do any harm if you scarify it using the hot water method mentioned above. At worst it will make little difference to the time taken in germinating, at best it could save you waiting a year or two.

If you want any more specific information on how to germinate a certain species then the list of suggested reading at the end of this article should be of help. Alternatively, you could always drop us a line (please enclose a stamped addressed envelope) and we will let you have whatever information we have on the plant.

Sowing the seeds

Now to look at some of the basic principles of seed sowing

Compost. This does not normally need to be very rich, the seed of most species (orchids are a notable exception) contains enough food reserves to feed the growing plant for the first period of growth. However, if the seedlings are not going to be potted up when small they may need feeding with a liquid feed. A good basic compost mix is:

• 5 parts good steralized loam, preferably sieved to remove lumps
• 4 parts sharp sand
• 5 parts well rotted leaf-mould
• 3 parts well rotted compost

Add one extra part sand if a well-drained mix is required, add one extra part compost if a rich mix is required. If an acid mix is required it might be necessary to buy it in unless your soil is naturally acid. If a neutral compost is required and your soil is naturally acid then it will be necessary to add some lime or seaweed meal to the compost mix in order to increase the pH to around 6.5.

Sowing the seed. The main thing here is to make sure that any pre-treatment has been carried out and that the seed is not sown too deeply (or too shallowly though this is normally less of a problem) and it is put into the correct type of seed compost. You start off by loosely filling the seedpot with compost level with the top of the pot. You then firm down the soil (either by sharply tapping the base on a solid object or by gently pressing the compost down with the fingers). The level should drop by about 11/2 to 2 centimetres and this is a good level for most seeds. Very small or surface sown seeds will need a little more soil put into the pot before sowing the seed, larger seeds will need to be pressed into the soil a little. The seed is sown by spreading it thinly onto the surface of the compost and putting a thin layer of compost on top of the seed, equal perhaps to twice the thickness of the seed. There are a number of deviations from this basic method. The major deviations are as follows:

• Surface sowing. The seed is put onto the surface of the compost, perhaps a tiny amount of compost is spread on top and then the seed is gently firmed into place. Surface sown seed is much more susceptible to drying out so it is most important that pots of surface sown seeds are kept moist, but not waterlogged.
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Covering the pots with newspaper and glass is an effective way of holding the moisture in and reducing the need to water, but make sure this cover is removed as soon as the seed starts to germinate.

Where to put the pot. Different seeds have different requirements in order to germinate. Most need light but some require a shady position. Some need a lot of warmth, others only a little, whilst others need a cold period before they will even think about germinating. Seeds that need warmth and light should go into a greenhouse or polyhouse. A special place may need to be made for those seeds that require a period of cold. This place must be mouse and squirrel free and may also need protection from birds. It also needs to be exposed to the elements so a special frame covered in thin-mesh wire is often used and positioned against a north facing wall. An alternative, especially if a plant does not require as much cold as our winters normally provide, is a well-made cold frame.

Aftercare Watering. is the main thing to be aware of once the seed is sown. The compost must not be allowed to dry out, but neither must it be waterlogged. The seed, especially as it starts to germinate, is very susceptible to drought or waterlogging and easily killed by either.

Getting the seed to germinate is only the start of course. Now you have got to look after the young seedlings so that they will eventually become mature plants. In the next newsletter we will take a look at this subject.

Further reading

Propagation of Trees, Shrubs and Conifers. by W. G. Sheat. Published MacMillan 1948
    A bit dated but a very good book on propagation techniques with specific details for a wide range of plants.

Seed Manual for Ornamental Trees and Shrubs. by A. G. Gordon. and D. C. Rowe.
    A very comprehensive guide to growing trees and shrubs from seed.
Hardy Woody Plants from Seed. by P. McMillan-Browse. Published Grower Books 1985.
    It does not deal with many species but it is very comprehensive on those that it does cover and covers the basic principles very well. 

This article is from Plants for a Future.

A beautiful article on soil 

We didn’t write this one, but an old friend did.

By Alex Stone, Dept. of Horticulture, Oregon State University

Soil health, is defined as: “the continued capacity of soil to: function as a vital living system within ecosystem and land-use boundaries; sustain biological productivity; promote the quality of air and water environments; and maintain plant, animal, and human health” (Pankhurst et al, 1997).  Soil health is vital to crop production and agro-ecosystem function

An often overlooked aspect of soil health is the ability of the soil to suppress plant diseases. One way to improve the soil’s potential to suppress plant diseases in field soils is through cover cropping and the addition of organic residues (e.g. manures, composts, or industrial organic wastes such as paper mill residues).  Organic residue-amended field soils have been shown to suppress a variety of soil-borne diseases.

The addition of organic residues to field soils can reduce disease by increasing the numbers and activities of beneficial organisms (e.g. organisms with potential for biological control of pathogens).  Beneficial soil microorganisms can directly inhibit the pathogen through competition for carbon and other nutrients (e.g. iron), competition for space, antibiotic production, and direct parasitism.

Composts have been shown to suppress root diseases caused by Pythium spp., Rhizoctonia spp., Phytophthora spp., and Fusarium spp. in a wide variety of plant species in containers (Hoitink et al, 1991). 

Organic matter-mediated suppression of these fungal diseases is potentially due to a variety of mechanisms: suppression of pathogen germination, destruction of pathogen resting structures and mycelia, competition for space and/or nutrients, and induction of systemic resistance in the host plant. There is also evidence that similar phenomena occur in organic matter-amended field soils

Manure additions and cover cropping suppressed Phytophthora root rot of avocado in commercial orchards in Australia (Malajczuk, 1983). Composted brewery waste applications have been shown to increase bean emergence, reduce snap bean root rot, and increase yield in New York field soils (Abawi and Widmer, 2000).  Grapevines from vineyards employing cover cropping and composting have been shown to exhibit significantly less root damage (due to Fusarium oxysporum and Cylindrocarpon spp.) than grapevines grown in vineyards in which these practices are not employed (Lotter et al, 1999).

Cover crops have been shown to reduce, increase, or have no effect on disease incidence depending on the host crop, cover crop, pathogen, and other factors.  A cover crop can act as a host for a pathogen, resulting in an increase in pathogen populations and disease incidence in subsequent host crops.  In other cases, cover crops can increase the populations of beneficial organisms and reduce disease incidence. Potato growers in eastern Washington are growing white mustard cover crops for suppression of Verticillium wilt (http://grant-adams.wsu.edu/agriculture/covercrops/green_manures/index.htm).

Snap bean root rot severity was shown to be reduced in container trials (with field soils) by the incorporation of ryegrass, oats, Trudan 8, grain rye, wheat, crown vetch, and rapeseed (Abawi and Widmer, 2000). 

  Plants may change the composition of the soil microbial community through selection of the microbes associated with their plant tissues – roots, leaves and stems.  Fusarium wilt of palm (caused by Fusarium oxysporum) has been shown to be suppressed by the growth of an understory leguminous cover crop.  This is thought to be due to an increase in the numbers of non-pathogenic Fusarium oxysporum and other Fusarium spp. in the soil, which compete with the pathogen for space and nutrients. 

Suppression was much stronger after 230 days of cover crop growth than it was after 49 days (Abadie et al, 1998). Sturz and Christie (1998) have shown that red clover harbors bacteria in its tissues that improve the growth of subsequent potato crops.  When red clover is grown in rotation with potato, the growth and yield of potato is enhanced.  Some of these red clover and potato–associated bacteria have also been shown to be active against potato tuber pathogens such as Fusarium sambucinum and F. oxysporum (Sturz et al, 1999).

Some crops, such as mustard family plants, can actually destroy pathogen propagules immediately after incorporation (Lewis and Papavizas, 1971; Muehlchen et al, 1990). These plants contain glucosinolates, which break down during soil incorporation into chemicals that have detrimental effects on the survival of fungal mycelia and resting structures such as sclerotia and chlamydospores.

A field trial was initiated in 1998 at the University of Wisconsin to determine the impact of organic amendment quality and quantity on the severity of common root rot of snap bean. Raw and composted paper mill sludge (PS) were applied because PS is a large volume industrial waste stream currently land-applied in WI on sandy soil processing vegetable acreage. Both raw and composted paper mill sludge strongly suppressed common root rot (Stone et al, 2003)

In recent work in Oregon, we have shown that fresh and composted dairy manure solids amended to field soils suppress root rot of sweet corn, and there is a strong relationship between disease suppression and microbial activity (Darby, 2003).  However, suppressiveness only lasts for one growing season, so manure must be applied each year (Darby, 2003). 

References:

• Abadie, C., V. Edel, and C. Alabouvette, 1998.  Soil suppressiveness to Fusarium wilt: influence of a cover-plant on density and diversity of Fusarium populations. Soil Biol. Biochem. 30:643-649.
• Abawie, G.S. and T.L. Widmer, 2000.  Impact of soil health management practices on soilborne pathogens, nematodes and root diseases of vegetable crops.  Appl. Soil Ecol. 15:37-47.
• Darby, H.M. 2003. Soil organic matter management and root health. Dissertation, Oregon State University, Corvallis.
• Doran, J.W., and M. Safley, 1997.  Defining and assessing soil health and sustainable productivity.  In: C.E. Pankhurst, B.M. Doube, and V.V.S.R. Gupta (eds.), Biological indicators of soil health.  CAB Intl.  New York, NY.
• Hoitink, H.A.J.
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, Y, Inbar, and M.J. Boehm, 1991.  Status of compost-amended potting mixes naturally suppressive to soilborne diseases of floricultural crops.  Plant Dis. 75:869-873.

an intentionally bioactive living matrix

by Joey Klein and Karl Hammer

Vermont Compost Company

Vermont Compost Company has been making compost and blending potting soils since 1993.  As participants in the growth of this business, and as an organic vegetable growers with  greenhouses, we are enthusiastic users of compost based potting mixes.  Karl originally developed potting soils for organic growers the early 80’s in Vershire, VT.

We were dissatisfied with the blends available that were made for use with chemical fertilizers.  The happy use of compost-based blends requires some changes in attitude and practice.  For growers who have been using potting media that are blends of peat, vermiculite, and perlite with a chemical wetting agent and  nutrient charge, there may be a learning curve to the proper management of plants in compost-containing media. For growers seeking to run their greenhouse within the criterion of certified organic production, there is no better choice than potting soils containing substantial amounts of appropriate compost

The compost in the potting media provides many benefits.  It emulates the growing conditions  to be found in a compost-enriched soil, where there will be a large, diverse, and vibrant population of microbes.  This microbial community is a proven suppressant of soil borne disease organisms.    The microbial interaction with the roots of the seedling results in a plant/microbe mediated release of nutrient ions from the humus, allowing the mix to meet the changing needs of the growing plant. The compost serves the role of organic matter in the soil, and as it is broken down its nutrients are slowly released, providing a long-term nutrient supply. The compost also provides sites for the retention of soluble nutrients from other ingredients. 

  Leaching of soluble nutrients is minimized. (For an excellent discussion of these issues, see Organic Soil Fertility Management, by Steve Gillman, Chelsea Green, 2002.)

There are some management issues in the use of compost based potting media.  The most important is maintaining adequate soil temperature, as you are working with a living system that will slow and stall if it is not warm.  Providing heat to the soil directly is ideal.  One strategy is to grow in soil blocks on a heated concrete slab.  Another is to have the forced hot air of the heating system delivered under the benches, where it will have to rise through the media.

A common approach is to install a hot water tank in your green house and water with tempered water.  If the water is 60 degrees when it goes into the potting media, it will tend to retain that heat.  If you water with cold well water of 40 to 45 degrees, it will take a lot of sunshine and forced hot air just to get back to the root zone goal of 60 degrees.   A hot water tank and plumbing to mix the water to 60 degrees (lukewarm) will more than pay for itself in saved heating fuel, and give visible results in rapid plant growth.

Compost and peat are both very water retentive.  Most mixes for organic growers contain no wetting agents.  This means that the media must be gradually wetted and mixed, usually by hand in small batches, until it is uniformly moist but not wringing wet

The higher the percentage of compost in the mix, the less watering the plants will need. 

Crushed granite, sharp sand, perlite, and vermiculite may be added to these mixes help with drainage and porosity.  In general, any potting soil with a large percentage of compost will require much less watering.  For growers just switching over from other mixes, this will be an adjustment.  They will most likely prefer a mix with more perlite and more rapid drainage.  Let the surface appear dry before watering.  Ideally, the media surface should be dry overnight. Even better is to invest in an “ebb and flow” bottom watering system.  Algae thrives on cool and damp soils, so the best control is to avoid these conditions

Growers producing food crops in the greenhouse need to be cautious in keeping a balance between soil temperature and the available light.  In low light, short photo periods, typical of late winter in , and in cold soil where there is soluble nitrate, plants can tissue accumulate large and potentially dangerous amounts of nitrate in the leaves. Of particular concern are spinach and mache.  Well made organic mixes tend to avoid this problem by minimizing nitrate availability. Cell, pot, or block size is crucial to the successful use of compost-based potting media.

With compost-based potting soils, the grower must provide adequate soil volume to meet the need of the growing plant, while balancing this with the need to minimize the heated area of the greenhouse.  Conscientious potting-on as the plant develops, and prompt setting out as the seedling reaches the correct stage to deal with the outdoors best achieve this.  Small-celled plug trays are possible with blends with a higher percentage of perlite, but the smallest cells are to be avoided.

Brenda Hedges of Greystone Gardens (Waterbury, VT), a plug producer, lists 144 cell trays as her smallest and sells many 98’s, 72’s and 36’s of plants to pot on to her organic greenhouse customers.

It is best not to try to meet the needs of a rapidly growing plant with any sort of soluble fertilizer.  Many that are approved for organic growers fail to live up to their stated analysis.  The smell of freshly applied fish emulsion in a retail greenhouse can be very off putting.  Much better is to move the plants to larger pots with a fresh charge of compost-based media.  For Julie Rubaud of Red Wagon Plants in Shelburne, VT, this means, choosing the 12 inch pot over the 8 or 10 inch for her premium hanging baskets.  She more than gains back the extra cost of the pot and the media in the selling price.

For organic vegetable growers needing a high volume of seedlings to transplant, the plastic-free option has its merits.  The Dutch have led the way in this technology, moving beyond the hand or stand up block maker to the block making machine.  Soil blocks require a media that will hang together well, containing no perlite at all.  Soil blocks provide an excellent environment for plant roots, with air on all sides and good drainage.

Sandy and Paul Arnold of Pleasant Valley Farm (Argyle, NY) even take trays of soil blocks to their farmers’ market and tear off plants as they sell.  Their customers appreciate the vigor of the plants and the lack of plastic trash.  The Dutch blocking machines are very quick, seeding and blocking automatically. 

Pete Seely of Springdale Farm (Plymouth, WI) has pioneered in the import of these machines and can answer all questions about them

Please do not tinker with adding additional fertilizers to a mix without the ability to test for electrical conductivity. Higher conductivity in potting soils will suppress germination of many plant varieties.  Some sensitive varieties want almost no nutrients in their germinating mix.  Conductivity meters are available from many catalogs, and are an essential investment if you are blending or adjusting your own potting media

An organic beginning for plants that will receive organic care gives them benefit of adaptation to the environment in which they will finish their growth.  This is a visible boon both to the farmer setting a crop to grow to maturity, and to a greenhouse grower selling plants to organic gardening customers.  Remember, under organic management we are not seeking to provide the soluble nutrients directly to the plant roots.  Rather, we should strive to create the appropriate conditions for the plants to communicate with their microbial communities via sugar/enzyme root exudates.  The plants’ microbial herds, given appropriate and sufficient humus in the media from which to work, will make available the appropriate nutrients for the plant’s stage of growth.  Organic growers need to leave behind the paradigm of direct feeding of the plants, and instead work to create the appropriate environmental conditions for the plants to husband their own bio-collaborative community, to make the right nutrients, (and other things i.e. communities of disease suppression), available at the right time.  Careful watering and soil temperature management are both crucial to your success in working with compost-based potting medias.