No-till Gardening in Clay soil

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    I was recently asked about gardening with clay soil. Clay soil is made up of very fine rock particles which creates a soil structure that is easily hardened and compacted. Seedlings often find it difficult to push up out of this heavy soil, and roots also are often crushed or limited in their expanse. The soil is easily water-logged, but when the soil dries, it becomes very hard. 

Clay soil hardens and cracks when left uncovered to dry out.

    It's not all that bad. During hot Missouri summers, clay soil retains water much longer than other soils. It also contains many nutrients; if we can just break up the soil, those nutrients will be available for our plants.

    As I am practicing no-till gardening, or rather, reduced till, my strategies would differ somewhat from those using conventional tilling. No-till strives to build the organic matter into the soil over the years by leaving the ground undisturbed while adding yearly deposits of mulch or compost overtop of the soil.

Adding Organic Matter

    Adding organic matter to the soil is the best way to remedy clay soils. Organic matter allows the water to filter through the soil to prevent water logging. It also breaks up the soil, allowing roots to expand their growth and penetrate deeper into the soil. 

    One could till into the soil peat moss or other organic amendments, such as compost. This I have done in the past, and it does help break up clay soil. For a very large and ever-growing garden, such as mine, the cost of peat moss becomes prohibitively expensive. 

    Then there are the endless arguments about the ecological impact of the removal of peat moss from its native environment. An alternative for now is coconut coir, but it is still too expensive for my budget. I should be able to solve this problem locally, I think. After all, this state is wild-life abundant!

    Composting is a great way to add organic material to the soil. Save all the leaves you can in the fall and other browns from early-spring cleanup, and build your compost pile by mixing in the summer "greens" such as grass clippings and garden waste. A simple ratio by volume is 3:1 greens to browns. 

My compost pile, enclosed by straw bales. Seedlings are placed over top, keeping warm under cover during chilly spring weather.

    Using the "no-till" or "no-dig" framework, a gardener would place the compost directly overtop of the soil, rather than tilling it into the soil. Because the sun is so hot in Missouri, I would add a layer of dried grass clippings or mulch on top of that to prevent the degradation of the compost.

    For the large garden, gathering enough compost can be a chore! Compost takes time to develop, so this is not my only method.

Mulch

    Each fall, I add leaf mulch overtop the garden patch. Leaves are best mowed over prior to topping the soil, as mowing destroys spores, reducing diseases in the garden. Smaller leaves also are less likely to be blown away by the wind and won't cover small seedlings from the sun. However, the intense Missouri sunlight and heat also quickly decompose the leaves, and smaller leaves decompose faster. Often by the end of summer, many patches in the garden have lost their leaf mulch due to decomposition. 

    Leaves should not be dug into the soil, as they deplete the soil of nitrogen as they break down. However, when they are used simply as a top-dressing, they provide mulch to suppress weeds and retain soil moisture. In this scenario, worms and other organisms decompose the leaves at the soil line, and recycle the leaf nutrients in their waste.

Here are onions growing out of leaf mulch applied in the fall.

    In the summer, my husband blows the grass clippings into small piles using our riding lawn. Grass, of course, is very tidy and easy to work with as a mulch, and also feeds the soil. I allow the pile to dry over a few days, and then I have my kids gather the grass and bring it to my garden, where I add it as mulch in a 3-4 inch layer. In my experience, the plants really love the grass mulch; they grow really strong in that environment.

    If the pile gets too big, it will start to rot. That stuff is ok for the compost bin, but it is better to have dry grass for your garden mulch.

Annual cover crops

    Annual cover crops are arguably the most effective method for adding organic method to the soil.   The roots aerate the soil and provide nutrition for micro-organisms. These tiny critters, in their waste and death, recycle this food as nutrition for plant growth. 

    Rather tilling cover crops into the soil, a no-dig strategy would sacrifice the crop by mowing, leaving the plant roots in place as nutrition for soil organisms. The top growth may be used as mulch or tossed in the compost bin. After the cover crop is killed, then crops are planted directly into the soil. 

A cover crop of winter rye and crimson clover about to be mowed.

    While I did till into a new plot of soil last year, I sowed overtop a cover crop of rye and crimson clover to feed the ground and establish a new root system. After mowing my cover crop, I laid black plastic over the area, which will remain in place for about three weeks to kill off any remaining weeds. Into this interval, I can add my summer crop. The land should be ready for planting by mid-May.

The black plastic I used (which can be purchased here) is 4 MIL plastic, which is about the thickness of the heavy-duty garbage bags you get at the grocery store and can also be used as landscaping fabric. Large, weather resistant tarps are extremely expensive, so this was the best I could buy without breaking the bank. I purchase lengths 10 feet wide, which gives space for a 4 foot wide bed and 1 foot path. It is important for me to keep bed spacing identical for all my beds, so I easily transfer the plastic between beds.

Perennial cover crops

    Perennial cover crops do much the same as annual ones. The use of the perennial covers I am still exploring. The perfect perennial would add nutrition to soil through the roots, provide some food for the gardener, provide ground cover for the soil, and also create habitat for important garden predators, such as birds and bees. 

    Of course, one plant can't fit the bill for every thing, so why not plant multiple plants to address the gardeners needs? For the home orchard, Stephen Sobkowiak recommends adding bushes on either side of each fruit tree, as well as around 10 other perennials to promote soil structure and other garden culture.

I planted sage below my orchard trees as part of a perennial cover crop.

    For the home orchard, where the cropping plant has a permanent location, perennial covers seem reasonable, and I am working in perennials around my fruit trees and bushes. For the vegetable plot, however, this strategy seems confining. I am still considering how to make it work. 

Water and Fertilizer

    If you haven't noticed, keeping an eye on the water levels with clay soils is important. While mulch does a lot to keep the soil moisture consistent, be sure to water the garden if it is getting dry. Plants grow very poorly in compacted soil, and clay soil becomes hard and compact when dry. 

    For the vegetable garden, consistent application of mulch and compost may be enough to maintain soil nutrition and aeration. However, if a soil test shows your garden needs a boost, or you want to ensure your heavy fruiting plants such as fruit trees are getting enough nutrition, I have seen many recommendations by organic orchardists for the use of basalt, which is rich in micro-nutrients and has been shown to increase soil health in nutrient-poor soils. The basalt I used can be purchased here, and I have also applied this organic Bio-Live Fruit Tree Fertilizer to my fruit trees.

Add basalt 12 inches from the base of the tree to the drip line.

    The application rate for basalt is 10 lbs per 100 sq-ft at planting, and another 5 pounds later in the growing season or 1 cup per inch of trunk for fruit trees.  Similarly for the Bio-Live fertilizer application recommends 1 cup per inch of tree diameter for pome fruit trees, such as apples, and 2 cups for stone fruit trees. These are applied from 1 foot away from the trunk to the drip line.

A soil test can be used to determine the health of your soil. I have used this one, which, actually, I really liked. It gives an in-depth analysis of your soil , and saves the test results online, which can be compared over the years you use their product. They also offer fertilizer appropriate for you soil, if you would want that. However I like to choose my own fertilizer. 

A note on seedlings

    Since I use mulch heavily, generally, I transplant older seedlings into my garden rather than direct seeding. However, certain vegetables, such as carrots transplant poorly. Mulch, which covers the ground from the sun, has a negative impact on small seedlings. Without mulch, the very top layer of clay will dryout and harden very quickly, and the weak seedlings to not have the strength to pop out of the soil. 

    My solution to this has been to remove the mulch, create the appropriate-depth trench, lay down the seed in the trench, and cover with potting soil or compost. Keep the plot well-watered. Choosing seeds that are recommended for clay soil also helps with germination and later growth. I re-mulch once the crop grows tall enough to stand over the mulch.

To promote direct seedling growth in clay soil, I lay potting soil over the top of the seed, rather than the clay soil.

There you have it; all the simple, no cost solutions to getting a garden out of your clay soil. These organic solutions take time, so be patient with your soil as you implement these changes.

Happy Gardening!

Here are the links to some of the garden tools and fertilizer I actually used as well as discussed in this post. Click to learn more:

Film Gard 4MIL Black Plastic Sheeting

Bio-Live Fruit Tree Fertilizer 

Basalt Rock Dust

My Soil Soil Test Kit