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Q At our new location, the only place we have for a vegetable garden is just 35 feet from the highway. I recall reading some time ago that poison from automobile exhaust can contaminate vegetables. Is there anything we can do to prevent the vegetables from absorbing lead fumes? Airborne lead from auto exhausts can indeed cause deposits on the foliage of vegetables, but it can also contaminate the soil (as can lead-based paints from demolished or standing buildings). A high fence or hedge should be placed between the garden and the highway to intercept the lead from the exhaust.

Two years ago plant physiologist Nina L. Bassuk of the Urban Horticultural Institute at Cornell University (Ithaca, N.Y.), found through her research that the more organic matter that was in the soil, the less the plants took up lead from the soil. In soils where decomposed organic matter (rotted leaves, manure, compost, etc.) made up 40 to 50 percent by volume of the soil, the lead uptake was zero, even though lead concentrates were as high as 3,000 parts per million.

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Lead deposits on foliage surfaces can be washed off with vinegar water at the rate of one tablespoon to two quarts. You could also use a very mild solution of liquid detergent in water. Rinse well after washing to remove any vinegar or detergent taste.

Q A year ago I planted some year-old asparagus roots. Even though I kept them watered, only a few shoots came up. So far this year there are still only a few shoots. I was told to plant the roots eight inches deep and am now wondering if that was too deep. Our soil is not clay, but heavier than sandy soil, and fairly well drained.

If your soil were sandy, you would plant the crowns only 6 inches deep, but if it is a heavier soil, as you describe, then 4 or 5 inches is sufficient. Deep planting inhibits shoot growth.

The easiest way to plant is to dig a trench and spread the roots out in the trench, covering at first with only 2 inches of soil over the crowns, and then gradually filling in as the shoots begin to spring up. In home gardens, plants can be spaced 12 to 15 inches apart with the rows about 30 inches apart. If there is only one row, leave 3 feet between asparagus and other vegetables so they will not compete.

Q I grow African violets on a stand with three shelves and fluorescent lights over each shelf. I have variegated varieties on the top shelf and the leaves are turning to solid green. What's wrong?

If you use foliar feeding, the leaves almost always tend toward solid green. Another reason might be that your soil is too alkaline.

You could use a simple pH test (testing equipment is available in garden stores). If your soil is pH7 or above, then you could add a very small amount of acidifier, such as that used for acid lovers like azaleas, to bring it down to pH 5, 6, or 7.

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Too high a temperature could be another factor. The top shelves are warmer than the bottom shelves, so move your plants to the bottom shelf to be nearer the floor where the temperature is cooler.

Q For the past two years I have tried to grow okra but cannot get the seed to germinate well. Is there some way to get better results? I sowed seeds after soil was warm and spaced them three inches apart, thinking I could thin plants to one foot apart. They came up unevenly, some as much as two feet apart.

Okra has a very hard seed coat. A good trick is to put seeds in a freezer for about eight hours and then put them in very warm water (tingly to your fingers) for about half an hour, just before sowing. Some folks merely soak seeds 12 hours; others rub the seeds gently between two pieces of sandpaper. Keep soil moist during germination period.

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