Rocky or sandy soil can make it difficult to grow plants. Heavy clay is also difficult to landscape. Here are some tips for dealing with difficult soils in the garden. First, some definitions.
Types of Soil
Picture a triangle, with the words silt, clay, and sand along the three sides. The type of soil you have depends on where your garden falls in this triangle. Silty loam is the best soil to have but is relatively rare.
Clay Soil
Clay causes problems because there are few pores, or spaces, in clay. Water and air compete for the scarce pores. Water tends to pool and take a long time to drain. Roots have a hard time growing through clay because the pores are hard to find. Roots also tend to rot in clay soil because of the water pooling in it.
Sandy Soil
Sandy soil is the opposite of clay. The grains of sand have lots of pores. Water drains very rapidly before plants can soak it up. Nutrients tend to leach out of sandy soil, leaving behind a dry, sterile growing medium.
Silty Soil
Silt is between clay and sand in the ability to retain moisture and release it back to plants. Silt is usually found in bottom lands and can be very fertile if conditioned properly.
Soil pH
pH is how acid or alkaline a soil is. The scale starts at 1, for the most acid thing in the world. Seven is neutral, and 14 is the most alkaline thing there is. Most plants, such as blackberries, prefer to grow in soil that is neutral or a bit alkaline. Other plants, like blueberries, strawberries, and azaleas, like soil that is pretty acid.
The acidity of the soil affects the availability of nutrients in the soil. For example, iron in acidic soils can be difficult for plants to absorb. While you can add lime to acidic soils to reduce their acidity and sulfur to alkaline soils to reduce their alkalinity, it is difficult to make a major change in the pH of the soil. It also takes several years of amending the soil to make a meaningful difference in the pH. You are better off planting things that are adapted to that pH.
Soil Depth
Soil rests on the bedrock below it. In some places, the bedrock is a long way below the soil surface. In other places, there is barely an inch of soil over the bedrock. You can tell how deep your soil is by digging a hole. If you can dig the hole two feet deep, you have plenty of soil. Don’t fill the hole in yet, you will need it to check the drainage of the soil.
Construction Compaction
Many places, especially landscapes around new buildings, suffer from compacted soil. While construction was going on, the machinery and traffic compact the soil so there is no space for roots to grow or air and water to enter the soil. Water frequently runs off without soaking in. Trees like pin oaks, red oaks, or other large trees that predate the construction often have problems because the soil over their roots becomes compacted. They begin to decline and often fall victim to pests and diseases.
Drainage
If you fill that hole you dug with water until it stops soaking in, you can access how well your soil drains. Come back in an hour. If the water level has dropped significantly, you have soil that drains well. If the hole is still full, you have poor drainage and will have to work to amend the soil, so it drains well. You may need to add topsoil to a low area before landscaping to improve the drainage.
Solutions For Difficult Soil
You can correct difficult soil so that you can grow a healthy garden. Here are some ways to make your garden thrive.
Add Organic Matter
The best way to treat any soil is to add organic matter. Mixing compost in the top foot of your soil will aerate it so roots, air, and water can pass through. Adding organic matter to sand gives water and nutrients something to stick to, so they are more available to your plants. Do not use uncomposted material such as raw manure to amend the soil. The microbes that decompose uncomposted material do so by using some of the nutrients the plants need, especially the nitrogen plants need to grow. Compost has already been broken down into nutrients plants can absorb.
Till Compacted Soil
If your soil is compacted, till it as deeply as possible. An effective way to do this is a broadfork. You can also use a pitchfork or a shovel to turn over the soil. You will only need to do this once, before planting anything. After planting, you should avoid stepping in the landscape bed or other landscaped areas. If a path is necessary, use pavers or other permeable material to prevent continued compaction of the soil.
Fixing Fill Dirt
During construction, fill dirt may have been used to level the property. This dirt is sterile and lifeless. Compost has the microbes this dirt needs to become soil. Mix three inches of compost into the top six inches of soil to jump start the transformation.
Differences in Irrigation
Irrigation should be done differently between soil types. Since clay has difficulty absorbing water, irrigation should be on for twenty minutes, then off until that water is absorbed. The best way to do this is to water the soil in one zone for twenty minutes, then cycle through the rest of the zones. Repeat this two to three times so the soil has adequate moisture but isn’t a swamp.
Sandy soil drains rapidly, so you can water it all at once. Too much water will leach the nutrients from sandy soil. Add one inch of water at a time.
Use Native Plants
Many difficult landscapes defeat common ornamental plants. if you use native plants, they are already adapted to the soil type, temperature extremes, and amount of rainfall in the area. The native plants available in your area will differ depending on where you are located and the soil composition of your landscape. However, almost any location has a range of native plants that grow in the area and are suitable for residential landscapes.
Use Raised Beds
One way to defeat difficult soil is to construct a raised bed. Placing a mixture of fifty percent topsoil and fifty percent compost in a raised bed one foot tall creates an ideal environment for most perennial plants to grow. Shrubs will do well in a raised bed, but most trees are too large for a bed that is a reasonable size. You will have to pick a native tree with care for it to fit in a raised bed. The raised bed will have to be considerably deeper for a tree than for a perennial.
We Can Help
At TN Nursery, our staff are gardeners and can recommend plants native to your area that will do well in your landscape. Give us a call at 931.692.7325 today.
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