GARDEN DOCTORS: Cover crops can improve soil

Gail Hall of Santa Rosa asks: What are the benefits of a cover crop for my vegetable garden?

Cover crops have the ability to improve soil conditions by breaking up compaction through root penetration, increasing organic matter, fixing nitrogen, suppressing weed growth, and preventing soil erosion of fallow ground.

Some people will purchase the nitrogen-fixing Rhizobium bacteria, which already exists in the soil, in powder form and inoculate or coat seeds with it immediately prior to planting, to ensure there is an adequate population of this bacteria.

A different innoculant is required to treat alfalfa and clover than the one that treats peas, beans and vetch.

Most cover crops are either legumes or grasses and sometimes they are sold as a mix.

Leguminous crops, such as clover, peas, and vetch, fix nitrogen by means of a symbiotic relationship between the plant's roots and the bacteria living in the soil.

Grasses, such as oats, rye and sorghum-sudan grass, are useful for adding organic matter, suppressing weeds, and for erosion control. Buckwheat is a warm-season crop that grows extremely quickly and is useful for smothering weeds.

Sow the cover crops by broadcasting seed over the desired plot that is relatively free of weeds, and in full sun. Ideally, the seed should be spread evenly. The "whirligig" and hand-pushed drop spreader (broadcast seeder) are very efficient tools to use. Broadcasting by hand will do, if you don't have either of these tools. Raking or discing the seeds 1-2 inches into the soil is recommended.

Keep the area damp and do not overwater. Just before you're ready to plant, incorporate the plant material into the soil by going over it with a lawn mower first, then work it into the soil.

Heidi S. of Sonoma asks: I have a large Magnolia x soulangeana (Tulip tree), that is doing quite well. Is it necessary to do any sort of pruning on these trees?

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