Q For the last two years our lettuce has become bitter after the first leaves are cut. We have used the same varieties as in the past. Leaves that come along afterward become tough very quickly, before we have a chance to harvest much of the lettuce. K.L.
Anytime lettuce growth is abnormally slowed, leaves can become tough and bitter. This can be caused by late planting when hot weather slows growth and changes chemical content. The same change in quality will result if plants are crowded or if soil is low in nutrients, organic matter, or both. Soil with low moisture content for even a short time can cause bitterness.
Mixing organic matter into soil and mulching will help remedy this. Lettuce not only tolerates cool temperature, but produces its most tender and flavorful leaves in early spring as soon as hard-frost danger is over, or in fall before heavy frost. Most lettuce varieties tolerate light frost.
A feeding of a balanced plant food as soon as leaves emerge helps maintain flavor and tenderness. Some varieties tolerate heat more than others, and most seed catalogs indicate which ones these are. Buttercrunch is a variety that does well in almost all parts of the country. It has tremendous heat resistance.
Q While we were in Florida, we read about a large bird kill on a golf course near the place we were staying. The article said the birds died from a nematicide. We are aware that nematodes can be a problem with many crops, but we would like to know if there is some kind of biological control that would spare our precious wildlife, as well as people. Certainly, anything toxic enough to kill that many birds must be harmful to humans.
R.R. and M.J.M.
There is a naturally formed chitin-protein nematicide being marketed by IGENE Biotechnology Inc., 9110 Red Branch Rd., Columbia, MD 21045.
The material is called ClandoSan (a registered trademark). It is made from chitin (KY-tin), which is the hard covering over the bodies of crustaceans - of which there are about 30,000 species, including shrimp, crayfish, crabs, and lobsters.
Researchers tell us that it modifies the behavior of normal microbes, which are already in the soil, stimulating these normal soil microorganisms to produce enzymes that destroy plant-pathogenic nematodes and their eggs. The company has a toll-free number: 800-346-6421.
As more and more home gardeners, farmers, and consumers demand a toxin-free environment, there will be increasingly greater progress in research and development of safe pesticides.
Q My neighbor's zoysia grass is invading my yard. It is an unsightly brown in winter, and I dislike it intensely. A few years ago I put metal flashing along the property line, but some had already moved into our lawn.
We prefer the fescue grasses and want to keep it free of the zoysia. What can we do to get rid of it and keep it from spreading? Is there a chemical we can use, or must we dig it by hand and reseed?
Two unfavorable features of zoysia grass are the ones you have named. While some folks like it because of its aggressiveness, others despise it. Unfortunately, any chemical herbicide you would use on the zoysia would kill the fescue (or any other grass) as well. Therefore, the only solution is to dig it while it is dormant, trying to get as many roots as possible. Then some good soil should be added to the bare spots. You can reseed it immediately. The sooner the better, so new seedlings can become established before more zoysia springs up. Feed the new grass as soon as it is up.
Q As a new gardener, I am confused about fertilizers, especially the numbers which appear on the different brands. Of those I saw in a garden store recently, I copied these numbers, which appear under the term ``guaranteed analysis,'' of five different brands: 23-19-17; 10-10-10; 22-20-18; 10-15-10; 8-6-5 (this one also contains yeast and bone meal). If these numbers mean percentages of each element (nitrogen, phosphoric acid, potash), what is the rest composed of?
When we were kids back on the farm, there was one standard fertilizer, 5-10-5. This meant it had 5 percent nitrogen, 10 percent phosphorus, and 5 percent potassium, all in a soluble form. The rest of the bag was filler, which was used to make the fertilizer easy to apply or spread at the recommended amount per acre.
As researchers became more aware of plant needs, they found that certain elements were needed in lesser amounts. For example, beets can get black spots and dry rot from lack of boron. Other plants may have need for copper, zinc, manganese, iron, or molybdenum. These are called ``trace elements,'' and they may be listed separately on the container, or just as ``trace elements necessary for good plant growth.''
Today, gardeners can choose: (1)fertilizers for dry application; (2)liquids that need to be diluted; (3)dry crystals to be mixed with water; (4)slow-release pellets; (5)spikes and sticks to press into soil. All, whether called ``organic'' or ``inorganic,'' must list the percentage of nitrogen, phosphorus, and potassium in the guaranteed analysis, and most of them have specific directions for application.
Many have three forms of nitrogen making up the percentage of nitrogen. Most use phosphoric acid for the phosphorus content. Potash is the potassium.
Phosphorus stimulates root growth, can hasten maturity, and stimulates seed formation. Potassium contributes to bloom and fruit formation and stiffens stalks. Nitrogen stimulates leaf and stem growth. Most garden plants need a balanced amount of each.
Doc and Katy Abraham are nationally known horticulturists.