A. Yellow leaves usually means either too much lack of fertilizer or cold/frost damage. I think in your case the yellow leaves are a combination of both. Unfortunately, there’s not much you can do about it this time of year. You really can’t protect a large lemon tree from frost, and you also don’t want to fertilize it this time of year. Fertilizer will only prompt new growth, and you don’t want new growth sprouting and then getting hit by frost and dying. Once danger of frost is over, fertilize with either a citrus fertilizer or some form of iron. You can even use both, as long as you’re careful about overfertilizing, particularly with the iron.
As for pruning, citrus do not usually require pruning. Prune only if a branch sprouts where you don’t want it to. For instance, into a sidewalk or garden path or into another landscape specimen. You can do such pruning anytime of year since it’s so minor.
Q. My son in San Mateo tried to grow tomatoes this past summer, but the results were disappointing. He thinks an infestation of tiny whiteflies was the problem. What should he do differently this summer if he decides to try again?
A. For one thing, he might have to move! San Mateo is often too cool to successfully grow great tomatoes. He might try a variety more suited for cool climates, such as San Francisco Fog. Even then, he must plant them in the hottest part of the garden, perhaps in front of a south-facing stucco wall where the plants might get reflective heat. Whiteflies are a common problem and can be somewhat controlled with a variety of sprays. He can choose chemical insecticides or Safer insecticidal soaps. Be aware that spraying must be done at dusk or else the little buggers just fly away.
Q. We have 2.5 acres of really bad clay soil. I read a past column of your’s that talked about planting a winter cover crops, such as fava beans, and then rototilling it under to improve the soil. Do you know where I can buy fava beans?
A. Planting a green manure will indeed naturally improve soils. Unfortunately, my calls to nurseries and feed stores in the area came up empty as for buying fava beans. You can. However, order seed by mail through Peaceful Valley Farms, P.O. Box 2009, Grass Valley, CA., 95945; phone (530) 272-4760. You can also order online at www.groworganic.com.
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