Improving Clay Soil Lodi CA
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California Landscape Contractors Association
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Improving Clay Soil
Improving Clay Soil
If your garden has heavy clay soil, you know what a challenge it can pose to plants, not to mention gardeners. Heavy clay drains slowly, meaning it stays saturated longer after rain or irrigation. Then, when the sun finally comes out and the soil dries, it forms a hard, cracked surface.
On the bright side, clay soils are usually richer in nutrients than sandy soils are. And clay's tendency to hold water tightly can be an advantage.
Here are some tips for making clay soil more manageable and easier to work.
Tools and Materials
- Soil test kit or commercial test
- Organic mulches: compost and aged manure, straw
- Wheelbarrow or cart
- Cover crop (wheat, rye, clover, or oats)
Test soil pH, and adjust as necessary. Clay soils are rich in nutrients, but if the soil is too acidic or too alkaline, those nutrients won't be available to the plants. Use a home test kit or send a sample to a soil testing lab, then follow the recommendations for adjusting pH. For most garden plants, a pH of 6.3 to 6.8 is ideal. Find a lab near you by checking in your telephone directory, or by calling your local cooperative extension office.
Add organic matter. This helps improve drainage and lighten heavy soil. It also provides nutrients for beneficial soil microorganisms which will, in turn, also help improve the soil. Before planting in spring, add compost and aged manure. A 2- to 3-inch layer worked into the soil to shovel depth is a good amount. Throughout the growing season, mulch with organic materials like grass clippings, shredded leaves, or additional compost. Since soil microorganisms literally "eat" organic matter, make a habit of continually adding it to your soil.
Build raised beds. Because clay soils hold water, creating raised beds can help improve drainage by encouraging water to run off. Raised beds can be a simple mound of soil, or can be constructed out of wood, brick, or stone. To lessen compaction, size the beds so you can reach the middle without stepping in the bed.
Mulch beds over the winter. Driving rain can really pack down bare soil, so keep beds mulched with organic matter both during the growing season and over the winter. A layer of straw over the beds will protect the soil from compaction and reduce erosion; it can also help minimize weed growth. In the spring, transfer the mulch to the garden paths.
Plant a cover crop. A cover crop is like a living mulch. Different cover crops are appropriate for different regions. In the north, winter wheat and winter rye are popular choices; in warmer regions, crimson clover and oats are commonly used. For a winter cover crop, sow after the last crops have been harvested. The following spring, simply till the plants into the soil, adding yet more precious organic matter.
Improving soil takes time, so don't expect overnight results. On the other hand, if you follow the above steps you should notice some improvement each year. Within a few years, you'll have rich, plant-friendly soil.
Add compost any time. However, if you are tilling in fresh or uncomposted organic matter, such as a cover crop, leaves, or straw, wait at least a few weeks before planting to allow the material to break down.
Photography By Sabin Gratz/National Gardening Association
Planting in Clay Soil
Heavy clay soil needs extra preparation to help plants grow. Never work clay soil when it is soggy or bone dry. If the soil is too wet, it will pack into hard clods. If it is bone dry, it will shatter into dust that will turn to mud, then brick. Bone-dry soil should be watered with at least an inch of water, and then allowed to soak in for 24 hours. Test the soil by squeezing a handful into a lump, and then push your thumb into the lump. If it dents like modeling clay, it is too wet. If it crumbles, then it is perfect to work.
Always dig a hole three to five times as wide as the root ball of the plant and about the same depth as the root ball. Digging a deep hole usually causes the plant to settle too deep which leads to crown rot disease. Avoid digging a hole with smooth sides, which encourages roots to circle the hole. Chop the sides with the point of the shovel to create slots, which force roots to grow into the surrounding soil. Pour a couple inches of potting soil or planting compost and sand into the hole. Add 1/8 to 1/4 cup, depending on the size of the hole, of a complete fertilizer that has the middle number, phosphorus, at least as high as the first number, nitrogen. I always use bone meal because the fertilizer lasts longer and will not burn the roots. Chop it into the bottom so the potting soil and existing soil are mixed. Pour more potting soil or compost onto the pile of soil and add 1/4 to 1 cup of fertilizer. Mix it together so it is about 1 part potting soil or compost and 3 or 4 parts existing soil. The potting soil or compost will improve both aeration and drainage. It is better to improve the existing soil with compost or potting soil than to replace it with potting soil. This is worth repeating. Filling the hole with rich soil is likely to cause root rot. Rich soil will absorb water quickly, but it can’t drain away through heavy clay soil. The rich soil will usually be even wetter than heavy clay and root rot is likely. When you improve the existing soil, it is easier for water and roots to move from the improved soil to the existing soil. The only exception is if you hit blue clay. Roots will not grow in blue clay because there is no oxygen in it. Replace blue clay with sandy topsoil mixed with the top layer of soil.
Place the plant in the hole and adjust its height so the crown of the plant, the line between the stem and the root, is 1 to 3 inches higher than the original soil level. Shovel the mixed soil from the pile into the hole and use the shovel blade to cut the soil into the hole. This breaks up the big chunks and works the soil down so there are no large air pockets. If there is burlap or twine around the trunk, loosen it so there is at least an inch of room to grow. Completely remove any plastic twine around the trunk. Otherwise the twine will cut into the trunk as it grows.
Level the soil off so the soil is at the crown of the plant. Avoid burying the stem or low branches. You can build up a ridge around the plant to hold water while it soaks in. During wet weather, level the ridge so water doesn’t stand around the plant. Watch out that the plant doesn’t settle and create a puddle at the base of the plant. That would encourage crown rot disease. When you water, give it enough water each time so it wets the entire ball of soil in the hole. Then let the surface dry out between watering. During hot weather planting, you may need to water every day, but it is important to let the soil surface dry out between watering so soil diseases don’t become a problem. After a couple of weeks the plant should need watering less often as the root system grows wider.
Attribution: Gardening advice and Bible meditations. Rod’s Garden
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