How to grow plate-size dahlias

If you want to maximize the size of your dahlia flowers, keep the main stems free of side shoots, allowing only the terminal bud to develop. This will result in one flower per stem, and is most effective when growing the large, dinner-plate-size cultivars.

The plants will need some support to prevent wind damage and the stems breaking from the weight of the flowers.

• Keep the following general rules in mind when harvesting most vegetable crops.

First, it is important to harvest vegetables when they are at the peak of their flavor. Younger plants and fruits are often more tender than those left on the plant longer. The length of time vegetables remain edible depends on weather conditions. High temperatures hasten maturity.

It is also important to handle them carefully during harvest time. Check the garden daily and remove any ripe, damaged or misshapen fruits. Fruits that are not easily removed from the plant, such as eggplant, should be cut with a knife.

Harvest on a regular basis to encourage production. Many plants - such as cucumber, okra and zucchini - will cease production if mature fruits are not harvested.

• This is the time of year to look for magnolia scale, an insect about the size of a pencil eraser. Typically found on the underside of magnolia branches and twigs, the scale is responsible for creating an overall thin condition on the tree.

The scale exudes a clear, sticky honeydew as it feeds on the tree. Black sooty mold is a fungus that grows on the honeydew. Gardeners often notice the black mold on magnolia leaves or structures under the magnolia before noticing the actual scale. The presence of this black mold on other types of trees can also indicate problems with other insects.

The mold itself is not the real problem. On small trees, simply pick off the scale and squash them. Other control measures include spraying with summer-weight oil or applying an insecticide when the scale is in the active crawler stage, generally in early September.

For trees with a history of magnolia scale, a late winter to early spring application of dormant oil provides good control for the scale.

If your tree is affected, provide extra water during summer to minimize stress. You should be able to get this insect under control with one or two treatments, so an annual program of spraying should not be necessary.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.