Even plants that love clay will appreciate a little help. Adding compost to the planting hole or amending the clay soil withMiracle-Gro® Organic Choice® Garden Soilwill give new plants a good start. The organic matter will loosen the soil and improve drainage.
For trees and shrubs, smaller plants and bare root plants may establish better than large plants because their roots will adapt better to the clay soils around them. Avoid adding sand because it will mix with the clay and form cement-like soil. Another way to improve soils is to plant a green manure - a plant that will grow during the fall or winter that you then till into the soil to add organic matter. Winter rye can be planted as a green manure in fall and turned under in early spring. The top 8-10 inches of soil, where plants' roots live, determine the success of your gardening efforts.
An ideal soil from a plant's perspective is 50% soil matter and 50% open, or pore space (which should be half-filled with water and half left open for air). Clay soil, and soil near recent construction, is often too compact to allow roots to "breath." Adding organic matter to the soil lightens soil structure (also called "tilth"). Soil structure is how the individual clay, silt, and sand particles are arranged, and is impacted by factors such as organic matter.
Clay without organic matter is like a flattened deck of playing cards. Adding organic material jumbles the cards, permitting water and oxygen to enter the soil. Soil amendments are materials that are worked into the top several inches of soil, to improve drainage and loosen the soil where plants grow.
Organic soil amendments can make a world of difference in heavy clay soils. Organic matter breaks down fast in our warm climate, so beds will need regular additions of soil amendments to maintain good soil structure and fertility. The mention of clay soil to many gardeners will probably make them shudder. I had a gardener once tell me that clay was meant for making pottery, not for growing plants!
Clay soils are mineral soils with very small particles. These are generally low in organic matter and have very small pore spaces, making it difficult for plant roots to penetrate and gather needed air and water. That's why too much clay in the soil can be a detriment to plant growth. Plant roots need a balance of air pockets and available water, but in heavy clay soils, air pockets are very small and scarce.
You can begin, on a small scale, to improve the soil by working in lots of compost or other organic matter. Choose flower or vegetable beds that you want to plant this year and spread a three or four inch layer of mulch on top. Work it in to a depth of at least six inches, deeper if you can. Continue to do this year after year to help "fluff" up the soil. If you start small, in beds you plan to use immediately, you can spread your soil improvement efforts throughout the yard over several growing season. Persistence will pay off and eventually you'll have a loamy-type soil that will drain well yet hold important nutrients and moisture.
Best is to add organic matter, particularly compost. Be sure and add when your clay soil is dry, as working in wet clay is not only quite messy but will compact it even further. Peat moss is sometimes recommended as an addition, but this breaks down quickly in wet and clay soils, and can create an undesirable bog.
As an aside, glomalin also benefits the soil, and earth in general, by storing carbon. 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.
The addition of large amounts of organic matter will transform clay soil. Both Black Gold Peat Moss and Black Gold Garden Compost Blend will do wonders. Add these products to your gardens at a ratio of one part organic matter to two parts soil for lasting fertility.
Be sure that they are well incorporated to help maintain air pockets and soil loft. These products will 'open' heavy clay soils, improve drainage, and allow water to move more freely. Once everything is incorporated, apply fertilizer as needed, and get planting.
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. 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. 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. For a home gardener with heavy clay soil creating a garden or planting in the landscape is a task. It is essential to work up and fortify the soil in all beds and planting areas.
Clay soil is easiest to amend when it has a light amount of moisture and is easily dug. Work up the soil with either a tiller or use a spading fork to manually break it up as deep as you can–a depth of 1 to 2 feet is good, depending on what you are planting. As the soil is turned over and loosened, it is gaining air pockets.
How To Break Up Hard Soil Expose the broken up clay to the sun and air for a while, then break it up further. Once the clay is as light as can be, it's time to add lots of organic matter. 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. Over the years of gardening and landscaping on this property, we continually had to battle the clay soils. Common soil amendments include compost, grass clippings, straw, shredded leaves, rotted manure and dried seaweed. 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. Hinder Root Growth - In addition to poor drainage, this dense clay structure will also hinder root growth.
It's not uncommon for plants growing in heavy clay soil to never grow outside of the hole they were originally planted in—stunting their growth both below the soil, and above. They become root bound just like plants growing in a container pot. Because the roots have a hard time penetrating the clay, plants will likely have shallow roots and need to be watered more frequently.
They hold more water than sandy soils and are often high in nutrients plants need. But clay soils can become so waterlogged that they deprive plant roots of oxygen, or so dry that they become too hard to dig in. To determine how much clay is in your soil, feel the soil. If you can roll moist soil into a ball that hangs together, it contains more clay. Fortunately, you can find plants that thrive in clay soils and soil amendments that will help you grow a wider range of plants.
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. 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 way to improve clay soils is to mix organic materials thoroughly with existing soil, explained Brewer. Peat moss and sand are NOT recommended for improving clay soil, and purchased topsoil is frequently no better than your existing soil. Purchased topsoil is useful for creating raised beds, but for most landscaping needs, it is better to amend the existing soil with organic materials.
If you do bring in topsoil, be sure to mix it thoroughly with the native soil. If new soil is just spread over clay, plants will not root into the clay, and the plants will dry out in hot weather. Be aware that unsterilized topsoil may contain weed seeds. 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. Another method to increase organic matter in clay soils is with cover crops.
These are crops planted as you prepare beds, for a season or year prior, or in fallow periods between annual crops such as flowers and vegetables. They consist of small grains and grasses like buckwheat, ryegrass, and oats. Legumes, such as clover, also benefit by "fixing" nitrogen from the air for use in the soil. Cover crops have additional benefits such as suppression of many weeds. 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. 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. 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.
To improve clay soil—or any soil, add organic matter. Compost, peat moss, or aged manure will improve the texture of clay soil aiding drainage and aeration. You can use aged compost from your compost pile or bagged compost or planting mix available at garden centers. Grit sand for breaking up and improving heavy clay soil.
It's extra work but worth spreading a one or two inch layer of grit sand across the clay soil before spreading the organic matter and digging the whole lot in at the same time. If you have an area of grass growing on clay soil it's wise to spread organic material, ideally compost, on the surface. This will do much to feed the shallow roots of the grass.
