Do you have an area in your yard where you just can't get anything to grow? Have you struggled repeatedly with a prized plant or tree that just won't thrive? If you know what type of soil you have and are watering properly, it may be time to dig a little deeper to find out what's going on.
Check your soil texture. It dictates the way your soil drains and the amount of nutrients available to your plants. Providing the appropriate amount of water across the entire bed and at the right time also is of utmost importance.
Soil compaction is the next thing to look for. When soil is compacted, the air pockets are compressed, making it harder for roots to expand and grow and therefore harder for the plant to take up water and nutrients. Soil becomes compacted by foot traffic, use of heavy machinery, working the soil in overly wet conditions or when proper amendments — organic matter — haven't been added.
To improve your soil, apply a 2- to 4-inch layer of compost once or twice a year.
Aerating, especially in lawn areas, also can be helpful.
Soil pH is another important factor; it determines how acidic or alkaline the soil is, which affects plant growth, soil bacteria, availability of essential nutrients and soil structure as well.
Acidic soil has a low pH, and extremely low levels can cause a plant to become stunted or die. Plants that thrive in acidic soil include blueberries, azaleas, rhododendrons, hydrangeas, gardenias, camellias, crepe myrtles and pine trees. Adding soil sulfur, peat moss or iron sulfate will decrease the pH level.
Alkaline soil is high in pH and is generally deficient in nitrogen and other important minerals. A high-alkaline soil has higher levels of sodium that may be toxic to plants. Plants that grow in alkaline soil include clematis, heuchera, delphinium and dianthus.
If your plants have pale green or yellowing leaves, that may be a sign of nitrogen deficiency. Plants may be stunted or have much smaller leaves than normal. To increase nitrogen, add good-quality compost; grow cover crops, such as fava beans, borage and vetch, in the offseason; or add coffee grounds to the soil.
The amount of soil organic matter — decomposed plant and animal residues -- really does matter. It has been called the most complex and least understood component of soils. High levels of soil organic matter improve water and nutrient retention; help fend off compaction and erosion; balance pH levels; and even bind harmful pesticides and trace elements, keeping them from polluting our watersheds.
To increase soil organic matter, apply compost and mulch, reduce tillage, leave grass clippings on the lawn and rotate crops in your garden.
Earthworms are an excellent and essential indicator of healthy soil. They create burrows in the soil, allowing water to move through the soil and roots to more easily expand and grow. Dig out about 6 inches of soil and count the number of worms you find. Three to five is a good indication of a healthy soil. If you don't see any, your soil is lacking in organic matter.
By UC Master Gardener Rebecca Jepsen
This article first appeared in the July 20 issue of the San Jose Mercury News.