It's easiest and gives the best results when you are creating a new planting bed. (A combination of several different organic materials is fine.) Then hand turn or till in to a depth of 6-12 inches. Yes, it is labor intensive, but the difference in how your newly planted plants perform will be noticeable. They will establish better, grow better, bloom better, and vegetables will produce better. Keep your new bed mulched and over time the soil will improve even more.
For vegetable gardens, using winter cover crops and tilling them under in spring does wonders for the soil also. Why should you improve your clay soil, especially for newly planted perennials, vegetables and annuals? Improving the quality with soil amendments—usually organic material—allows better penetration of air and water to the roots. Organic material provides a home for the microorganisms that further improve soil structure and nutrient capacity.
The looser soil texture of amended soil versus heavy clay soil allows roots to grow more freely, and a larger root system makes for stronger plants. Take all these factors together and well-amended soil results in better nutrition, better drought tolerance, less water use and stronger growth for whatever you plant. You can improve clay soil, but don't work it when it's wet, and avoid walking on it so it doesn't become compacted. When it's dry, add three to four inches of organic materials, such as compost, leaf mold or well-rotted manure , and work them into the soil about six inches deep.
Mulch the soil with bark, wood chips or some other type of mulch that decomposes slowly. Over time, the sun and rain break down the mulch, which will also improve your soil. Cover crops, also called green manure crops, help loosen clay or compacted soils with their roots and by adding organic matter. They also prevent nutrient loss and erosion during the non-growing season.
Leguminous cover crops, such as winter rye, alfalfa, hairy vetch and clover, which add nitrogen to the soil, are usually planted at the end of summer or early fall. Compaction is most likely to occur with heavier soils like clay and loam, but when heavy equipment is used, sandy soils can become compacted. These are soil particles that are packed closely together. The problem may be compounded by events that have happened to the soil over the course of years. The pore spaces are reduced to the point that air and water cannot move freely and plant roots cannot grow easily into the surrounding soil. The soil could remain overly wet longer than is healthy for the plants growing there.
Organic matter in soil serves as food for earthworms, insects, bacteria and fungi-they transform it to soil nutrients and humus. Through this decomposition process, materials are made available as foods to growing plants. In finely textured clay soils, organic material creates aggregates of the soil particles, improving drainage and making it easier to work.
Earthworms are especially helpful in making and keeping soil porous and well draining, said Brewer. Many gardeners today, including myself, are doing no-till gardening. Instead of tilling the soil they are keeping a permanent organic mulch on top of their garden beds. You can still easily fertilize the soil with liquid nutrients or compost, and use foliar feeding throughout the season to get nutrients to plants at the proper times of the season. Along with adding compost, a second strategy for adding organic matter to my clay soil is cover cropping. I plant cover crops any time the beds in my garden would otherwise be unplanted or fallow.
Fallow periods provide little additional organic biomass while allowing the decomposition of organic matter in the soil to continue. They contribute to the improvements in soil structure that I described earlier. And they can smother weeds and even suppress weed seed germination. Many cover crops will also suppress pathogenic nematodes, for example root knot nematode. During the initial, pre-garden phase of my soil improvement plan, I managed to break up 10 inches of hard-packed clay with endless swings of my trusty mattock. I spread compost over the surface of the beds an inch at a time and rototilled it in.
I was careful not to work the clay when it was too wet, because clay worked wet can result in some tenacious clods, very reluctant in their willingness to ever come apart again. I tried to work the compost deep into the soil, and along with it, I added lime and phosphorus, the clay soil in my garden needing both. When surface-applied, neither of these materials moves down through the soil, so incorporation to ample depth is very important to permit roots to grow into the subsoil. After 3 to 4 inches of compost, I had the "raised bed" I wanted. I know you said no to raised beds but if flooding is a regular issue, it may be worth considering. You don't need to have wooden surrounds but simply pile the earth up so that it is a few inches higher than the footpaths.
As already mentioned, lots and lots of compost, manure etc dug in will greatly improve the soil structure, but you will have to do this every year. My plot is at the bottom of the hill and prone to waterlogging rather than flooding, and the saturation levels rot down the materials very quickly and soil goes back to heavy clay. The "raised" beds help to drain it quicker so water doesn't compact it so much. In autumn I also make trenches in beds and fill with autumn leaves - come spring, the soil is loose and easy to turn over.
Gypsum is easily applied to the soil surface with a regular lawn spreader. It's an ideal amendment for improving soil structure and relieving compaction in existing lawns and gardens. Some people claim you can loosen clay by adding gypsum to it. The theory is that gypsum binds clay particles together to make bigger particles, providing more space for air, water, and roots. While this works to some extent, adding gypsum alone isn't enough for most gardens. The best way to loosen and improve clay soil is by adding lots of organic matter.
This heavy, often dark, smooth soil is made up of very fine particles between which there are small air spaces. It is difficult to cultivate, being sticky when wet, yet hard and even cracking, when dry. In situations where drainage is poor, plants can rot because of waterlogging and a lack of air around the roots. Clay is also a cold soil taking time to warm up in spring, which can slow a plant's root growth. On the upside, clay is not only richer in nutrients than sand, but also retains nutrients and holds water well.
Amending your soil properly can overcome heavy, compacted clay and get it back on track for healthy lawn and garden growth. Adding materials such as organic compost, pine bark, composted leaves and gypsum to heavy clay can improve its structure and help eliminate drainage and compaction problems. Mulching – Clay soils can tend to speed water runoff because water isn't absorbed as quickly into clay soils as it is other soils.
Clay soils also tends to stick to the bottoms of your shoes, which can make a mess when you go indoors. By adding a layer of mulch to clay soil, you not only help keep the house clean, but can reduce the number of weeds that sprout. As mulch decomposes,it will enhance nutrition and water retention, which ultimately allows for better plant growth. Mulch will slow down water run-off allowing clay soil more time to absorb, and store, water. A layer of mulch is also cooler than exposed soil which helps to reduce temperatures overall in the garden.
Good soil provides just the right space between its particles to hold air that plants will use. Silty and heavy clay soils have small particles that are close together. Sandy soils have the opposite problem; their particles are too big and spaced out. The excessive amount of air in sandy soil leads to rapid decomposition of organic matter. Organic soil is rich in humus, the end result of decaying materials such as leaves, grass clippings and compost.
Good organic garden soil is loose and fluffy — filled with air that plant roots need — and it has plenty of minerals essential for vigorous plant growth. It is alive with living organisms — from earthworms to fungi and bacteria — that help maintain the quality of the soil. Proper pH is also an essential characteristic of healthy soil.
Healthy soil typically is more than 40 percent pore space, with large pores that promote drainage and small pores which help store water. This combination enables air and water to penetrate, promotes good drainage, and allows soil organisms to breathe and plant roots to grow. Machinery, foot traffic and pounding rain compact the soil and make life in the soil difficult. Compacted soils can flood and also be susceptible to drought, since water runs off rather than infiltrating. You can repair compacted soil by rebuilding its spongy structure. Common soil amendments include compost, grass clippings, straw, shredded leaves, rotted manure and dried seaweed.
In a garden bed, the best way to introduce organic material without digging , is to apply layers on top and let nature do the work for you. Simply pile your garden bed high with organic material – it can be wood chips, shredded paper, straw, chopped leaves, lawn clippings – whatever you can lay your hands on. It might be slow, but the wait will give you time to get to know your land before you plant. About half of a healthy soil is made up of mineral particles like sand, silt and clay plus organic matter. That is the room for air and water movement around the mineral particles. Pore space is required in order to have a healthy environment for plant roots and beneficial microorganisms and earthworms to break down plant residue into organic matter.
Bark, sawdust, manure, leaf mold, compost and peat moss are among the organic amendments commonly used to improve clay soil. Two or three inches of organic materials should be spread and rototilled, forked or dug into the top six or seven inches of your garden beds. The best products we have used to break up and transform clay soil are the liquid bio-tiller, Penetrate, and Blend. Penetrate contains powerful ingredients that work together to break up hard, clay soils. It comes in two bottles; Bottle A contains food for aerobic bacteria while Bottle B contains live aerobic bacteria. The live bacteria and other ingredients work together to break apart hard soil and allow air and moisture to circulate to plant roots.
Penetrate in conjunction with Blend is the fastest way to improve drainage and turn hard clay into dark, crumbly soil that is easy to work with. Heavy clay soils are quite dense, do not drain well and tend to be hard and crack when dry. Because there isn't much space between the clay particles, there usually isn't much organic matter or microbial life in the soil. Plant roots have a hard time growing in the hard material. Most heavy clay soils benefit from the addition of gypsum. It adds some nutrients but, more importantly, it loosens clay soils and makes it more workable.
Spread about 3 to 4 pounds of gypsum per 100 square feet over garden soil after it has been dug in the winter. Work it into the soil or allow it to be washed in by rain. The main consideration in improving sandy soils is to incorporate as much organic matter as possible to supply humus. Most sandy soils are seriously lacking in humus and so have a very poor structure, the soil being unable to hold water and plant foods. The humus acts as a sponge and ensures adequate moisture during dry periods.
Apply plenty of organic matter every year for it quickly disappears in this type of soil. Also apply a general-purpose fertilizer in spring, prior to sowing and planting. During wet weather and in autumn and winter, clay soils can become waterlogged and this will affect the health of plants.
When a soil is holding too much water the oxygen supply to the plants' roots is reduced and if this condition continues over too long a period the plants may die. In hot weather during spring and summer, clay soils can become as hard as rock; because as they dry out, the clay particles shrink, making cultivation almost impossible. In the last article in this series, we looked at how to prepare soil ready for spring planting. In an ideal world, the winter would be the ideal time for digging over the garden.
So the elements have a chance to work on the soil before cultivation begins again in the spring. It is during this digging that you can do much to improve difficult soils. Surprisingly often, people imagine that the proper way to improve dense, clay soil is to add the opposite kind of mineral material—sand.
After all, loamy soils, viewed as ideal garden soil, are a mixture of sand and clay. Unfortunately, when sand is added directly to clay, the result is something that more accurately resembles concrete. The reason loamy soils are great for plants is that they have a large ratio of organic material in them as a foundation for the sand and clay. Without lots of organic material, clay plus sand equals an awful garden. Clay soils are best improved with the addition of compost and other organic materials only.
To improve your soil, you'll need to add 6 to 8 inches of organic matter to the entire bed. Grass clippings (as long as they haven't been treated with chemicals), shredded leaves, rotted manure, and compost are all perfect choices. The organic matter needs to be mixed into the top 6 to 12 inches of soil. Digging it in and mixing it with a shovel is a great way to do this, as it moves a lot of earth without pulverizing the soil particles the way tilling can. However, if digging is just too hard on your back, using a tiller is a fine method. Vegetable gardens benefit from a top dressing of organic compost in spring and/or fall or in mid-season.
Simply pull away any mulch and spread two to three inches of compost or well-rotted manure over the soil. You don't need to work the compost into the soil; it will break down naturally and release nutrients. As a bonus, top dressing can help discourage weeds from growing and help the soil retain moisture. Your soil test or extension agent can help you determine the right amount of organic matter for your soil. As a general rule, when possible, add a layer of 3 to 6 inches of organic matter on your soil before planting, and work it down into the top 10 to 12 inches—where most roots grow.
In following years, build on your efforts by adding 1 to 3 inches of organic mulch as a topdressing each year.1 As it decomposes, it continues to gradually improve clay soil. Walking on your lawn or garden when its wet is a common cause. Heavy, beating rains also drive clay particles together. Salts from fertilizers and winter de-icing solutions build up in heavy clay as well. Clay's potential as one of the best soil types for plant growth lies in its unique properties. Managed well, clay soil typically requires less irrigation and less fertilizer, and leads to healthier plants all around.
However, major losses in soil organic matter content can take place when the soil is inverted or mixed annually by tillage. Extensive tillage stimulates microbial activity , and the consumption of mass quantities of organic matter ensues. After your clay soil becomes more friable and you have provided a deep root zone for your garden plants, you should consider reducing tillage.
Because the soil remains undisturbed, fertilizers and other soil amendments do not become homogenized in the tillage layer. Plant feeder roots, therefore, tend to proliferate in the top 2 inches of fertile topsoil. Lack of pore space means that clay soils are generally low in both organic matter and microbial activity. Plant roots are stunted because it is too hard for them to push their way through the soil.
