Always consider how large a tree or shrub will be at maturity while planning your landscape. Allow enough space between perennial plant and structures and one another for the plant to reach full size. Trees need to be at least 10 feet away from the house or the branches will rub holes in the roof, overhang and walls.
In a vegetable garden, overcrowding will result in low yield and quality. Vegetable plants grown from seed should be thinned while they are still seedlings.
At planting, transplants should be allowed enough space to reach maturity. In general, sweet corn, tomatoes, peppers and eggplants can be planted into 40-inch beds. Within the row, sweet corn plants are spaced about 3 inches apart; tomatoes, about 18 inches; peppers and eggplants, about 24 inches apart.
Melons are usually planted on 80-inch beds. Cantaloupes are spaced about 12 inches between plants. Spacing for watermelons is usually 30 inches.
Using disease-susceptible plants
Even within closely related groups of plants, some species or varieties are much more susceptible to disease than others. Disease-resistant plants can be much easier to maintain. If the plants you choose are less susceptible to common fungal diseases, the need for protective fungicide sprays can be reduced or even eliminated.
Some vegetable varieties are resistant to certain diseases. For example, many cantaloupe varieties are resistant to powdery mildew and many tomato varieties have resistance to Verticillium, Fusarium and nematodes.
Seed and nursery catalogs often list disease resistance in plant descriptions.
Giving plants incorrect exposure
Different types of plants have different sunlight requirements. Many common ornamentals native to desert or Mediterranean climates and vegetable plants will perform well in full sun to part shade. Ornamental species of tropical origins tend to perform much better in more shaded areas. Consider the conditions you have in your garden area while selecting plants. In most nurseries or garden departments, the shade plants will be separated from those that require more sun. Typically, the sun requirement is stated on the label.
Shade plants grown in intense sun turn yellowish, grow poorly and can sunburn. Avoid placing shade plants in a south or west side of a structure.
Plants that like sun are often stunted and spindly when grown in the shade; if they grow at all, they are usually spindly and have few leaves or flowers.
Poor lawn fertilization
Lawns should be fertilized several times a year. Insufficient amounts of nutrients can result in a thin, weak stand of grass that allows weeds to invade.
Typically, nitrogen is the most important nutrients supplied by fertilizer. The nitrogen requirement of your lawn will depend upon what type of turf it is and the soil type. A general recommendation is 3 or 4 pounds of nitrogen per 1,000 square feet annually in three or four applications. Tree roots will compete with the turf for nitrogen, so if there are many tree foots in the turf, slightly increase the nitrogen rate.
The amount of actual fertilizer you apply will depend upon how much nitrogen is in the type of fertilizer you have selected. Of course, the higher the concentration of nitrogen, the less you will have to use. Do the math to figure out how many pounds of fertilizer will be required per year to give your lawn the nitrogen it needs and divide by the number of applications you want to make.
Grass can be damaged by an over-application of fertilizer. The grass can turn brown, at least temporarily when too much fertilizer is applied at once.
Misapplication of pesticides
It is not uncommon for gardeners to misuse pesticides. An over-application of a material can result in the injury of a plant and the use of too diluted a rate or in an otherwise inappropriate manner can result in the failure of the material to provide control of the pest. In addition, misuse of a pesticide can be dangerous to the environment or individuals in the area or those that would eat fruit or vegetables from those plants.
The labels on pesticide containers contain important information that will help you avoid making these mistakes. These products are carefully tested before they are sold to the public and the labels spell out the result of this work. Information regarding how much material to use, when to use it, how to apply it and safety and environmental considerations are all spelled out on the label.