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, creating 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. Just break up the soil, and those nutrients will be available for garden 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. 

However, if you do till, you can till into the soil organic matter and amendments listed in this post.

You can read more about garden soil preparation methods here.

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. 

You can use common organic matter amendments such as compost, peat moss, or coconut coir. These amendments can be found at local garden shops, but you can also make compost using  ingredients from your own back yard. 

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.

Peat moss and coconut coir can be used in the same way as compost. However, because of their fine structure, keep them well-watered and add mulch overtop.

There are those who are concerned about the sustainability of peat moss. This is driven, in large part, by loss of peat habitat in Europe. However, Canadian peat moss reserves remain steady, so North Americans can continue to purchase peat moss without concern. Coconut coir is also renewable.

 If you are interested, you can find product information on peat moss and view coconut coir products here.  

Mulch

For the large garden, gathering enough compost can be difficult, as compost takes time to develop. 

However, mulching also benefits clay soil over time; worms and other soil critters consume the mulch layer above and re-deposit it in their decomposed droppings when they travel below the soil surface.

Use whatever mulch you can find. Here I discuss the mulches I use.

Leaf Mulch

Each fall, I add leaf mulch overtop the garden patch. Leaves are best mowed over prior to topping the soil. This 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 decompose smaller leaves 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 or tilled into the soil, since leaves deplete the soil of nitrogen as they break down. When they are used simply as a top-dressing, they provide mulch to suppress weeds and retain soil moisture.

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

Grass

In the summer, my husband blows the grass clippings into small piles using our riding lawn mower. Grass, of course, is very tidy and easy to work with as a mulch. It also feeds the soil. 

I allow the piles 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. 

Cover Crops

Cover crops are highly promoted and used by large scale organic growers and associations. They improve soil structure and drastically reduce pest pressure by giving winter habitat to predators.

I am experimenting with incorporating cover crops into the home garden.

Annual Cover Crops

Annual cover crops are arguably the most effective method for adding organic materials 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 than 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 vegetable crops are planted directly into the soil. 

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

Last fall, I gave cover crops a try. After tilling up some new garden beds, I sowed overtop a cover crop of rye and crimson clover. 

After mowing my cover crop this spring, I laid black plastic over the area for three weeks to kill off the remaining weeds. Into this plot, I transplanted tomatoes, peppers, and other vegetables around mid-May.

The black plastic I used 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. 

Click here to find out more about the black plastic I purchased.

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 can easily transfer the plastic between beds.

Perennial cover crops

Perennial cover crops do much the same as annual ones, but I am still exploring their use. I think it makes sense to use a perennial cover crop along side a perennial regular crop, such as fruit trees. 

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 add multiple perennials to address all the gardeners needs? 

For the home orchard, permaculture orchardist Stephen Sobkowiak recommends adding bushes on either side of his fruit trees, 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 perennials into beds containing my fruit trees and other fruiting bushes. 

For the vegetable plot, however, this strategy seems confining. I am still considering how to make it work. 

Water and Fertilizer

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, many organic orchardists use basalt, which is rich in micro-nutrients and has been shown to increase soil health in nutrient-poor soils. 

 Learn more about basalt I purchased here. 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 MySoil Test Kit, which I found very convenient. It gives an in-depth analysis of the soil, and saves the test results online, which can be compared over each year the gardener uses the test kit. 

They also offer fertilizer appropriate for the gardener's soil, based on the results of the soil test. However I like to choose my own fertilizer. 

A note on seedlings

Since I mulch heavily, generally I transplant older seedlings into my garden rather than direct seeding. However, certain vegetables such as carrots transplant poorly. 

Mulch covers the ground from the sun and has a negative impact on small seedlings. Without mulch, the very top layer of clay will dry out and harden very quickly, and the weak seedlings do 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 a small amount of 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.

Organic solutions take time, so be patient with your soil as you implement these changes.

Root Slayer for Clay Soil

There is one reliable tool I use for gardening with clay soil. The Root Slayer has a narrow spade with a serrated edge. 

This tool cuts through clay really well, which is important when digging tree holes or splitting perennials. If you don't happen to get enough mulch on your garden, this tool makes removing pernicious weeds like dock easy. 

I actually prefer this to the trowel for planting transplants because it allows me to stand while making holes.

Learn more about the Root Slayer on Amazon.

Happy Gardening!

Here are the links to some of the garden tools and fertilizer I actually used as well as discussed in this post. Thank you for supporting this website. 

Click to learn more:

Radius Garden Root Slayer

Film Gard 4MIL Black Plastic Sheeting

Bio-Live Fruit Tree Fertilizer 

Basalt Rock Dust

MySoil Test Kit

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