Ecology and Pest Management
  The Rhizosphere
  The Phyllosphere
  Animal Pests

The real science in horticulture comes from observations and record keeping. Taking notes on daily or weekly walks through the garden during the growing season is highly recommended. These notes can include information on any observed insect damage, nutrient deficiencies, microbial diseases, or weeds. It is also necessary to keep a record of any treatments that you apply, and the results. These notes will help you make decisions about changes that you may need to make for the following year.

It is most important to remember that you remove nutrients from the soil by harvesting plants and that you must return nutrients to the soil. Plants that do not receive sufficient nutrients are more prone to attack by insects and microbial diseases. On the other hand, soils that are overfertilized have a reduction in the beneficial microbes that recycle nutrients and help prevent disease. Regular maintenance and best management practices that limit the amount of chemical fertilizers help to keep plants healthy.

Organic gardeners build up the soil with regular incorporation of compost and keep the pH in a range between 6.5 and 6.8 to ensure plant-available nutrients. Compost can be sprinkled onto the garden and does not have to be dug in. You can also sprinkle compost on your lawn. When you mow your lawn, you should allow the clippings to stay there. This returns nutrients and lessens the need for the addition of nitrogen fertilizer.

Exposed soil often forms a hard, crusty surface as water evaporates. The next time you water or the next time it rains, the water will run off the hard surface instead of penetrating into the soil. This is desirable in the desert, where desert crusts develop bacterial communities that prevent erosion and add nutrients to the soil. In the garden, the crust needs to be broken up and turned into the soil. A garden tool called a cultivator has metal prongs that are used to break up the hard surface of the soil. Adding mulch to the top of your exposed soil can prevent this crust from forming.

Botrytis cinerea grows on a young
Figure 5.4 Botrytis cinerea grows on a young
petunia plant. Plant diseases caused by Botrytis
fungi commonly infect vegetables, ornamentals,
fruits, and some field crops. It is one of the most
frequent causes of infection in greenhouse plants.
Spread of the disease can be controlled by the
removal of the dead or dying leaves and flowers.
Many herbaceous flowering plants bloom longer if they are deadheaded. When the bloom begins to wither, it is removed from the plant and added it to the compost heap. Decaying blooms and dead leaves are susceptible to gray rot, a fungal disease with a fuzzy gray appearance caused by Botrytis cinerea (Figure 5.4).

Purchased plants have to be inspected for pests such as mealy bugs, mites, white flies, or aphids because they can be transferred to your garden. Plants that are spindly, wilted, or have damaged leaves may carry microbial diseases and should not be bought.

Plants should not be crowded closely together, as this promotes the spread of fungal diseases through poor air circulation. The garden should be thinned as it is growing to allow plants room to spread. The recommended distances between plants are provided on seed packets or tags with transplants. Thinning involves removing weaker crop plants or weeds to allow the larger, healthy crop plants room to grow. Perennial plants must be divided every few years; otherwise they will get too crowded and decline in health. They are dug up either in the spring or fall, depending on the cultivar, then are separated and replanted.

Climbing plants need to be provided with a structure to climb. Fruiting plants are more prone to disease if they are lying in the soil. Crops such as peas, beans, squash, and cucumbers can be trained to climb lengths of nylon string that have been attached to a wooden frame, or on a trellis. Crops such as raspberries and grapes need to have support structures as well. Tomatoes usually require staking, as do many tall flowering plants. The weight of the fruit or flower may cause the stems to droop. Therefore, they are attached loosely to a stake.

Woody ornamental plants are pruned once a year or less often to remove dead branches, and sometimes live branches, to change the shape. Pruning is accomplished with a tool called pruning shears, which comes in various sizes to accommodate plants with branches of different diameters. Small saws are used on tree limbs. Trees and shrubs can be damaged if they are not pruned correctly. Fact sheets on the maintenance of woody plants are readily available through the horticultural extension service.