Annual flowers include some of the most colorful plants in home gardens. With a little extra care during early and mid-summer, you can keep them attractive right up to frost time.

The first rule in keeping annual flowers blooming is to cut off dead flowers so they won't go to seed. True annuals die after setting seed, and even those plants that don't die will be reduced in vigor.

The second rule is to cut back and fertilize plants when they become tall and leggy. Petunias, pansies, sweet alyssum and ageratum all continue to grow and flower at the tips of their shoots. As a result, plants spread out and after awhile become thin and unattractive. When this starts to happen, you use a knife or shears to cut them back to the small side shoots that occur low on most stems.

At the same time that you cut back plants, give them some fertilizer and a good soaking. Use either a soluble fertilizer and apply it according to the label, or dissolve about one-third or one-fourth cup of garden fertilizer (5-10-10) in three gallons of water. Then give each plant a good soaking. You can use this same treatment for plants in hanging baskets that have become ungainly.

Though these treatments work well for late summer blooms, they won't be effective enough to give you a good fall display of annuals. For fall blooms, it's better to start new plants to replace over-aged specimens.

Petunias started now will be ready to set out in late August or the beginning of September. They will grow vigorously until frost, and the brilliance of their flowers will be unequalled by plants blooming now in the summer heat.

Also consider starting some plants that thrive best in the cool autumn nights. Calendulas, for example, don't like the summer heat, but plants started now will give flowers until frost. Cosmos, both the tall types in mixed colors and the smaller orange and yellow flowered kinds, also bloom best in late summer.

Clumps of bearded iris are the highlight of many early summer gardens. They give a colorful display between spring bulbs and summer annuals.

Best of all, they are nearly maintenance-free if established in a well-drained, sunny location. However, most bearded iris need to be divided about every five years to relieve crowding and improve performance.

Divide them shortly after all blossoms have faded so new plants will have a chance to get established before winter. Here are some basic steps:

Cut leaves to about one-third their height, dig underneath and lift the entire clump. Wash away soil with the hose so you can see the root structure clearly. Using a sharp knife, cut rhizomes into sections so that each has one or two growing points or fans of leaves, a few inches of healthy firm rhizome, and a number of strong feeder roots.

Plant in full sun where soil is well-drained. Add compost or peat moss to improve drainage and a little 5-10-5 fertilizer in poor soils. Mix thoroughly.

Prepare a shallow hole and place each rhizome or clump on a slight cone of soil so that the top of the rhizome is just at or slightly above ground level and roots are spread below and around it. Place clumps about 18 inches apart. Fill the hole and water immediately.

"Growing Green" is contributed by Lehigh County Extension Office Staff and Master Gardeners. Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-746-1970.