Q. Plants do not thrive in my garden, and I suspect my soil is the problem. Is there anything I can do to improve soil without importing a load of topsoil?
Barbara Daily, Santa Margarita
A. Soil quality is important in gardening. Soil in good physical condition (good tilth) can hold and provide nutrients, water and air to roots. It will also drain well in rainy winters and be easy to work without becoming too sticky when wet or crusty and hard when dry.
This is the ideal, but in our county we often work with soil that is either sand or heavy clay. Our plantings generally would prefer medium textured loam.
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Luckily, poor soils can be improved by amendments of organic matter — compost is an excellent amendment, while manure, sawdust, leaves or lawn clippings can also be used. Any of these will improve soil texture, but nitrogen should be added along with non-decayed brown amendments such as leaves or sawdust, because these take up soil nitrogen as they break down; green amendments such as fresh lawn clippings require no additional nitrogen fertilizer. Amendments should be well dug in for best results.
Not all soil problems are caused by soil tilth. If you have inherited an old garden, it may be that previous owners made extensive use of fertilizers that led to a build-up of salts; or perhaps the soil is naturally too alkaline or acid. Laboratory testing is necessary to diagnose these problems and some solutions exist to remedy them.
Soil compaction during building is a problem that new home owners run into. The top soil may have been scraped away when the lot or foundation was prepared. Fill-dirt may have been brought into parts of the yard and may have very different properties. Such problems may need to be diagnosed by digging deeply in the soil. Strata of compaction and deep-lying problem soil should be considered when planning new gardens.
Choice of soil amendments will depend upon time and money available. It is probably not necessary to amend a whole garden. A beginning would be to amend soil only in planting holes to about three times the size of the transplant or in a specific area like the vegetable garden. Local Master Gardeners can give more information on soil amending.