Before any garden problem can be corrected, or plant damage prevented or controlled, it is necessary to know the cause. Sometimes this is very evident, but more often it is not. In the latter case, expert help is needed which can be had from county agents of your state agricultural service, some garden centers, botanical gardens and professional horticulturists.
Unfortunately, all too few local salesmen handling pest control materials are trained diagnosticians, or even experienced gardeners. In any case, no one can prescribe a cure without seeing the damaged plant, the pest that causes it or, in some cases, without having a soil analysis.
The Causes of Trouble
Before blaming an insect pest or disease, check the following possible causes, one or more of which may be to blame.
The soil. Has it been properly prepared by adding at least 5 per cent organic matter? Has sufficient fertilizer been applied to maintain adequate growth? If not, growth may be stunted. Has too much fertilizer been used so that the roots have been damaged? This may produce scorched edges on leaves, and in more severe cases the plants wilt and die.
Putting fertilizer in the bottom of a hole without thoroughly mixing it with the soil before setting in the plant is a common cause of damage. Applying more fertilizer than recommended on the package may injure plants. Letting fertilizer stay on the foliage may burn it. Always wash or shake off any fertilizer that falls on the foliage.
Sunlight is necessary for plant growth. Some plants require all-day sun to thrive. Without it they may not bloom or grow as well as they should. On the other hand, some plants cannot stand full sun and must be given protection, and they, along with shade-tolerant plants, are best used in shade plantings.
Climate. All too often we try to grow plants that are not adapted to our climate and although they may survive a few years, in less congenial seasons they may be damaged. For example, the evergreen magnolia of the South is being grown in many places in the North where it is never likely to live to a ripe old age. Many azaleas now being shipped from the South to northern gardens may also prove to be tender.
Temperature is often a limiting factor. Low winter temperatures will damage or kill plants that are not completely hardy. This damage may not be apparent until early summer, as is often the case with roses and broad-leaved evergreens. Sudden drops in temperature, especially in the fall before plants are sufficiently hardened, may damage them. High summer temperatures will restrict growth of some plants, whereas cold summers will limit the growth of more tropical plants, many annual flowers, and such vegetables as corn, melons, squash and tomatoes.
Wind is sometimes a limiting factor. Broadleaf evergreens and some needled evergreens (hemlocks) may be so dried by wind that the leaves scorch. The corners of a house, the narrow place between buildings, wind-exposed hilltops and open country are likely places for wind problems. Wind hitting a building and bouncing back may cause more damage than normal. All wind damage is usually worse on young plants before they have become well established.
Chemicals. Over-doses of chemicals used in the control of insects and diseases may damage the foliage. When the temperature is over 85 degrees, many dusts and sprays will burn even when used at the recommended strengths. Sulfur is especially dangerous to plants when the temperature is over 85 degrees F.
Another unexpected source of trouble is from careless use of weed control chemicals. Many of these are difficult to remove from the sprayer, so a separate sprayer is advisable. The drift of herbicide dust or spray onto particularly sensitive plants may do more harm to them than to the weeds themselves.
Pay attention to these details and you will have a thriving garden.
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