September in the Garden

If you don't already have a compost pile, September is an ideal time to begin putting end-of-the-season garden leftovers to work.

Start by layering grass clippings, spent flowers, and fallen leaves in a pile with a handful of fertilizer and a little moisture. Next month add perennials and annuals nipped by frost, vegetable crop remains, and even more leaves.

While the best compost starts with a diversity of organic matter, some things are better avoided. Because they are slow to decompose, stems or branches larger than 1 inch in diameter should be chipped instead. Don't add meat, bones, and oils that often attract animals. And keep out diseased plant materials and anything treated with herbicide.

Over time, the natural process of decomposition turns garden debris into a rich organic mixture. The compost can be used as a soil amendment to improve texture and fertility, or as a surface mulch to suppress weeds, conserve moisture, and moderate soil temperatures.

For homeowners looking for easy ways to "green" their gardening practices, a compost pile is an easy place to start. Recycling garden debris means less waste being transported to area landfills,

Other projects for your garden:

Trees and shrubs

Deciduous trees and shrubs can be planted or transplanted after they begin to drop their leaves or show fall color, signs they are entering dormancy.

Broad-leaved and needled evergreens, both dwarf and standard, are best planted or moved by Oct. 1. Water deeply and thoroughly at planting time.

Continue to water large trees and shrubs, especially evergreens, until the ground freezes hard. Evergreens lose moisture through their needles throughout winter and must have adequate water in their root zones to avoid winter burn or desiccated needles.

Wait until October to fertilize trees or shrubs that might benefit from extra nutrition, e.g. plants with stunted growth, undersized fruit, or off-color foliage. Avoid fertilizing healthy trees and shrubs to prevent unnecessary garden chemicals from entering groundwater and lakes.

Flowers

Winter protection of roses is not necessary until late November when the ground has frozen hard after several days of temperatures below 20 degrees.

Continue to deadhead both annuals and perennials to encourage additional flowers.

Do not cut back perennials until their leaves and stems have lost all green color.

Peonies can be divided or planted early this month. Water well to encourage healthy root development. Peony buds or eyes should not be deeper than 2 inches below soil level. If planted too deeply, they will fail to flower.

Refresh annual containers with cool-season favorites such as pansies, ornamental kale, chrysanthemums or fall-blooming asters. Asters and mums purchased in bloom are not necessarily hardy. To increase their chances of surviving winter, plant them directly in garden beds so they can establish roots for four to six weeks before frost. After frost mulch immediately and continue to water well.

Make final selections of spring-blooming bulbs but don't plant any until later in October or November.

Lawns

Early this month entire lawns or bare patches may be seeded with appropriate sun seed mix. Keep soil moist until seeds germinate. Water often until grass is established.

Midmonth is a good time to fertilize lawns. Choose an organic or synthetic product with a 3-1-2 or 4-1-2 ratio. Water fertilized areas well following application.

Core-aerating lawns can help to solve problems with compacted soil, heavy thatch accumulation, and poor drainage. Professional lawn services can provide the equipment or service. Leave plugs of soil on lawns to decompose. Avoid this procedure when soil is wet.

Edible plants

Continue to harvest vegetables as they ripen. If an early frost threatens, harvest warm-season crops such as peppers and tomatoes, and cover these plants with baskets or light blankets.

Begin to harvest late-season squash and early pumpkins. Full-size pumpkins need to remain on the vine as long as possible to achieve maximum size.

Begin to harvest second crop of any cool-season lettuces, spinach, peas, radishes or chard that were planted in August.

Continue to snip hers to use fresh, to dry or to freeze. Discontinue harvesting once herbs have gone to flower or seed.

To improve flavor allow collards, kale and brussels sprouts to experience frost before harvesting.

Maintain good sanitation. Remove diseased plants immediately as well as those that have finished producing. Add only healthy plant material to compost piles.

Houseplants

Carefully check houseplants that spent summer outside for any sign of insect or disease before bringing them indoors. Gradually introduce these plants to indoor conditions unless a premature frost threatens. Consider repotting with fresh soil but do not change size of pot until spring.

• Denise Corkery is a horticultural writer at the Chicago Botanic Garden