September is a good month to rejuvenate your garden for the fall and winter growing seasons. It's the time to divide and plant bulbs and perennials, to prune and to fertilize.
There are still weeks of steamy summer weather to go, but the end is in sight for another year. So spend some time getting your garden in shape after its summer of lush (and sometimes out-of-control) growth.
Divide and conquer
There are three reasons to divide perennials: to control the size of the plants, to increase their number, and to help rejuvenate them, especially older plants.
Gingers are among our finest perennial plants. During the summer they have produced an abundance of growth. To assure good growth next year, dig up and divide rhizomes, their underground horizontal stems. You will be amazed at how rapidly they will grow when they are given more room.
Shell ginger (Alpinia zerumbet) is a vigorous grower that produces magnificent pinkish, shell-shaped flowers that look like a cluster of grapes. This variegated leaf ginger will survive in the hot sun, but prefers part shade for best growth. Propagation is easy. You can dig up a rhizome and move it almost any time of the year, but September is an ideal time because we usually get frequent rain showers this month. The gingers require little care other than moist soil and occasional fertilizing.
Day lilies (Hemerocallis spp.), which have grown prolifically during the summer, are now beginning a short period of dormancy. Over time these perennial plants produce a thick clump of growth; its density can result in weak plants that do not bloom well. Now is the time to divide them. Dig the entire clump out of the ground and separate each individual plant. There will be a large tuber-like growth on the root system. Do not remove it. This is a storage organ that helps to promote further growth.
Set day lilies a little higher than they were in the original clump. After you have them divided and planted, fertilize lightly.
Stokes aster (Stokesia laevis) is another perennial that has a tendency to become too dense, so it should be divided now. The long, large roots may be reduced to make transplanting easier. As with the daylilies, many plants are in the clump. They should be separated and set slightly higher than their original depth.
This is also the time of year to dig bulbs. Separate and plant the small bulbs that form around the large central bulb, and then replant the older bulb. Amaryllis (Hippeastrum) has a tendency to draw its bulbs into the ground. When replanting, make sure that the top third of the bulb is exposed. If the bulb is planted too deep, it usually will not flower.
This applies to other bulbs in the Amaryllis family, such as spider lily and/or alligator lily (Hymenocallis spp.) and rain lily (Zephyranthes spp.), which can also be divided and replanted this month, along with the large crinum or swamp lily (Crinum americanum).
A properly pruned shrub is a work of art and beauty. Shrubs should look natural to fit into the landscape. Plants sheared into various geometric shapes foster a very formal look.
The first step is to remove all dead, diseased or injured branches. Pruning shears and saws should be dipped into a weak alcohol or bleach solution to prevent spread of disease. Remove branches that cross each other and those that look out of place. If the shrub is still too thick, remove older branches.
Cut back excessively long growth to a bud or lateral branch that is 4 to 6 inches below the average branch length. The shrub can be further reduced in size by cutting back each branch 4 to 6 inches to a bud. Using hand pruners to cut each branch separately will maintain a neat, informal shrub that retains its natural shape.
Pruning bougainvillea should be done before the middle of September to ensure good blooms this winter. Fertilize lightly with 12-4-8 or 15-0-15 or other similar mixture labeled for acid-loving plants.
The beginning of September is the last chance to prune your poinsettia before Christmas. The rule is not to prune after Labor Day. Keep your plants watered, and fertilize lightly.
Time to feed the lawn
September is also the month to fertilize lawns. Fertilizer applications are effective only when applied correctly. A complete fertilizer such as 16-2-8, 15-0-15 or a comparable mixture may be used. Spreader calibrations are important, not only to ensure good coverage but also to avoid damage from overapplications. You can access the fact sheet "How to Calibrate Your Fertilizer Spreader" on the Internet at edis.ifas.ufl.edu/LH024, or send a self-addressed, business-size envelope with 42 cents postage requesting that fact sheet (please ask for it by name so we know what to send) to 12520 Ulmerton Road, Largo, FL 33774-3602.
Plants to fertilize in September include azaleas, gardenias, camellias, ixora and ornamental trees with less than a 6-inch trunk diameter. Mature shrubs and larger trees do not need fertilizing; they will get plenty of nourishment when you treat your lawn. Other plants to fertilize are avocados, bananas, bromeliads, grapes, papayas and early vegetables.
This is the last time this year to fertilize many plants. Fertilizer helps maintain healthy plants and also prepares them for cold weather. A healthy plant can withstand adverse conditions much better than a weak, neglected plant. Use a fertilizer with a lower nitrogen number (the first number) than potassium (the last number) such as 8-2-12 to fertilize now.
Palms should also be fertilized now. Look for the 8-2-12-4 Palm and Landscape Blend recommended by the University of Florida to keep palms healthy and free of nutrient deficiencies.
Compiled by Pam Brown and Carol Suggs of the Pinellas County Extension Center/Florida Botanical Gardens. Questions? Call them at (727) 582-2100.