Extension Consumer Horticulturist, Clemson University
Can you explain to me the differences in garden lime? Which form is best? —J.N., by E-mail
Answer: Limestone is added to gardens to increase the soil pH, improve the availability of nutrients, encourage biological activity, and improve soil structure. In garden jargon it's called sweetening the soil. One commonly used type is calcitic limestone (or calcium carbonate), which contains about 40 percent calcium. The other is dolomitic limestone (or calcium-magnesium carbonate). This contains 21 to 30 percent calcium, and 6 to 11 percent magnesium. Dolomitic limestone is often recommended when soil tests indicate deficient levels of magnesium.
Both of these liming materials can be purchased in a ground or pulverized form resembling fine dust. To make them easier to spread with a centrifugal-type lawn spreader, both types are also available in pellets that dissolve when it rains.
Whatever lime you use, apply in accordance with the results of a soil test. Limestone is relatively insoluble in water (only 1 pound will dissolve in 500 gallons of water), so it's best to thoroughly mix the limestone into the soil. Apply it at anytime of year, but fall and winter arc the most effective times. Rain, snow, and frost heaves help it work into the soil.
When using calcitic or dolomitic limestone, you can expect an increase in pH to register after four to six months. For a more rapid change in pH, commercial growers use quicklime or burned lime (calcium oxide and/or magnesium oxide), as well as hydrated or slaked lime (calcium hydroxide). Both of these white powders change the pH rapidly when added to soil, the quicklime faster than hydrated. However, both are corrosive, difficult to handle, and have a high potential for burning or injuring plants.
Reading the label of an insecticidal soap, I came across “potassium salts of fatty acids.” Can you tell me what those are and how they kill insects? Can I use dishwashing liquid as a substitute for insecticidal soap? —G.C., Hollywood, CA
Answer: Potassium salts of fatty acids are created by adding potassium hydroxide to fatty acids obtained from animal fat or plant oils. The resulting “soap salts” are most effective in controlling soft-bodied pests, such as aphids, scale and mealybug crawlers, thrips, whiteflies, and spider mites. Generally, they have little effect on beetles and other hardbodied insects (an exception being cockroaches). The soaps must come into direct contact with the pest to be effective. The soap penetrates the outer cuticle of the insect s body and dissolves or disrupts the cellular membranes, causing dehydration and death. Soaps can also block the spiracles, or breathing pores, in the insect's body, which interferes with respiration. In some cases soaps may also act as an insect growth regulator, affecting the metabolism of cells and metamorphosis.
Certain common dishwashing liquids and laundry detergents, mixed with water, have also shown insecticidal and miticidal properties. When applied to an assortment of vegetable crops, Palmolive, Dawn, Joy, Ivory, and Dove, for example, have effectively reduced populations of whitefly, aphids, and spider mites. However, dishwashing and laundry detergents are not labeled as insecticides. Although they may be insecticidal, they are chemically different from the registered insecticidal soaps. Furthermore, they may prove phytotoxic, causing injury by dissolving the waxy cuticle of the plant's leaf surface. It is better to save these soaps for the chores for which they were designed.
I am having difficulty rooting stem cuttings of mountain laurel. I've taken cuttings at various times of the year and used rooting hormone, but I haven't been successful. Can you share any tricks? —S.C., Alexandria, VA
Answer: Mountain laurel (Kalmia latifolia) is an attractive evergreen shrub or small tree. Its native range extends from New England to the Florida panhandle and west to Indiana. Many consider it to be one of most beautiful flowering shrubs in North America. The flowers range through varying shades of white to pink, and the evergreen foliage is used in winter holiday decorations.
Unfortunately, mountain laurel is also difficult to root from cuttings. Over the years an assortment of approaches have been proposed by nursery professionals and researchers. No consensus has been reached. However, the experts agree that some cultivars root more easily than others. The easiest to root include ‘Bullseye’, ‘Carousel’, ‘Nipmuck’, ‘Olympic Fire’, ‘Pink Charm’, ‘Pink Surprise”, ’Quinnipiac', and ‘Sharon Rose’.
It is also true that cuttings root more readily from young plants than older ones. Cuttings of one- to two-year-old seedlings can be rooted even without rooting hormone.
The best approach for a gardener like yourself is to take cuttings in early January after your mountain laurels have been exposed to cold, satisfying their dormancy requirements, Take four- to six-inch-long cuttings and wound the lower ends by removing a three-quarter- to one-inch-long sliver of bark from opposite sides of the stem. Dip the cuttings in a rooting hormone, such as Dip 'n Grow (10,000 ppm indole-butyric acid and 5,000 ppm naphthalene acetic acid), and insert them in a pot or trays of a moistened soilless mix composed of two parts sphagnum peat moss and one part perlite. Water the trays, then place them inside a polyethylene bag to maintain high humidity levels. The cuttings can be placed in a cold frame with heating cables maintaining a bottom heat temperature of 70-75°F. The warm temperatures will accelerate rooting, but are not necessary for inducing roots. Alternatively, leave the cuttings indoors in a bright, southwest-facing window, but out of direct sunlight. Expect rooting to occur in three to five months.
Instead of trying to root cuttings, you might consider layering some branches by pegging them down in the soil. Layering occurs slowly in mountain laurel; it may take two growing seasons for an adequate root system to develop. If you can't bend a branch down to the ground, air layering is purported to work as well, although the long time required for roots to form makes this a less attractive alternative.
Can I save corn seeds from this year's corn and plant it next year with good results? —N.A., Derry, NH
Answer: Corn seed can be saved, but the quality of next year's crop depends on the parentage of the seed. Left to its own devices, your wind-pollinated corn will readily cross with other varieties, resulting in a hodgepodge of traits.
Because pollen is shed from tassels and carried on the wind, you will need to plant your corn far enough away from other corn varieties that are tasseling at the same time, to avoid contamination. Although pollen can travel half a mile, a distance of of 500 feet should yield 99 percent purity. If adequate isolation is not possible, you will have to hand-pollinate the silks yourself. It is important that you avoid self-pollination. Bag the tassels of at least 50 plants and the silk-bearing ears of 50 others. Collect the pollen from the tassels, and mix it together in one bag. Then, shake it onto the silks of corn in the other group.
Leave the ears bagged until harvest. Allow the ears to become completely dry on the stalk. Then collect the seed from 25 to 50 ears by rubbing two cobs together. Try to dislodge equal numbers of seed from each ear. Discard any kernels that are not fully formed. To test the moisture content of the corn seed, hit it with a hammer. A fully dried kernel will splinter into pieces when hit with a hammer. Store the seed in a cool dry location for up to three years.
For more details on the saving of vegetable seeds, read Suzanne Ashworth's book Seed to Seed. The second edition is available from Seed Savers Exchange in Decorah, Iowa (www.seedsavers.org).
My pecan tree dropped a lot of pecans in late summer, just when I thought I'd have a bumper crop. The pecans have perfect holes in them. When I cracked them open they were all wormy inside. What can I do next year to prevent these worms from getting at the nuts? —H.P., Trinity, AL
Answer: The worms are the larvae of pecan weevils (Curculio caryae), the most serious late-season insect pest of pecans. This weevil also attacks hickories, walnuts, chestnuts, oaks, beeches, and 'hazel-nuts. Commercial growers use monitoring traps to determine the precise time to spray to control the adult weevils.
Once the larvae are inside the nuts there is nothing that can be done. If your pecan tree is large, your best strategy is to concentrate on sanitation. Gathering up the fallen nuts and composting them will reduce the rate of infestation next year.
Alternatively, plant late-maturing cultivars, such as ‘Cheyenne’, ‘Desirable’, ‘Kiowa’, or ‘Moreland’, which are less likely to be attacked by the weevils. H