Continue to deadhead both annuals and perennials to encourage additional flowers.
Return of cool weather is a good time to refresh annual containers with cool-season favorites such as pansies, ornamental cabbage and kale, chrysanthemums, or fall-blooming asters. Asters and mums purchased in bloom this month are usually greenhouse-grown and not necessarily hardy. To increase their chances of making it through the winter, plant them directly in garden beds, rather than containers, early this month so they can establish their roots for a good four to six weeks before frost. Water well and mulch plants right away.
Do not cut back perennials until their leaves and stems have lost all green color.
Daylilies and peonies can be divided or planted early this month. Water well to encourage healthy root development. Peonies should be planted so that the buds or eyes are no deeper than 2 inches below soil level. If planted too deeply, they will fail to flower.
Make final selections of spring-blooming bulbs but don’t plant any until later in October and November.
Early this month, entire lawns or bare patches may be seeded with appropriate grass seed mix.
Grubs chew grass roots, and they may be present if your turf begins to brown and lifts easily off the ground. Minor damage is usually not cause for treatment. Pull back turf and check for white, C-shaped larvae with black heads. If more than 10 to 12 grubs are present in a square foot of soil, treatment is advised. Chemical controls vary in their timing. Homeowners can spot-treat small areas immediately with a recommended control or, wait until the third week of next June to apply imidacloprid. As temperatures become cooler in fall, the grubs will move further down in the soil, making them out of reach of chemicals.
Consider core-aeration of lawn, if not done this year. Professional lawn services can provide the equipment (and the service itself) to remove plugs of soil and grass at regular intervals over entire lawn. Plugs are left on lawns to decompose. Core-aeration is recommended to help rectify compacted soil, heavy thatch accumulation, and poor drainage. Avoid this procedure when soil is quite wet.
Midmonth is a good time to apply fertilizer to lawns. Choose an organic product or a synthetic fertilizer with a 3-1-2 or 4-1-2 ratio. Moderate temperatures this month along with cool nights and adequate rainfall will spur grass growth, making September a good time to feed turf.
The next six weeks will provide an abundance of produce. Continue to harvest vegetables as they ripen. Warm-season crops like peppers and tomatoes must be picked as soon as possible. If an early frost threatens, cover these plants with baskets or light blankets. Refrigerating tomatoes causes them to lose their flavor. Store in a cool, 60- to 70-degree room for a few days.
Begin to harvest late-season squash and early pumpkins. Full-sized pumpkins need to remain on the vine as long as possible to achieve their maximum size.
Allow collards, kale, and Brussels sprouts to be hit with frost before harvesting. This improves their flavor.
Begin to harvest a second crop of any cool-season lettuces, spinach, peas, radishes, or chard that were planted in August.
Continue to snip herbs to use fresh, to dry, or to freeze. If herbs have gone to flower or seed, discontinue harvesting, since the flavor has then left the foliage.
Everbearing raspberry bushes will produce their fall crop on the top half of the canes. After harvest, prune out the top half of the plants. The lower half of the canes will produce fruit early next summer. After harvesting the summer crop, prune the canes to the ground.
Maintain good sanitation throughout the vegetable garden. Remove diseased plants immediately as well as those that have finished their growth cycle for the year. Compost only healthy plant material.
Cuttings from favorite or unusual varieties of annuals such as geraniums, coleus, begonias, and impatiens can be taken this month, potted up, and brought inside to a south-facing window. Some tender unusual container plants can be brought inside as whole plants — hebe, black mondo grass, mandevilla vine, and certain small geranium plants are a few. Many gardeners prefer to repot the plants and change the soil to a fresh, lightweight, soilless mix at this time.
Houseplants that have spent summers outside should be monitored in the event of a premature frost. Check plants carefully for any sign of insect or disease before bringing them indoors. Gradually reintroduce these plants to indoor conditions. Consider repotting and changing soil at this time. Do not change size of pot until spring.
Amaryllis bulbs that have summered outdoors must begin their dormant period. Remove bulb from container and shake off all dirt. Cut back all foliage, whether it is yellow or green, and set bulb on its side in a cool, dark room for several months until new growth appears.
To create a winter herb garden, dig up selected herbs such as thyme, basil, rosemary, or oregano. Repot in smaller pots, change soil to soilless mix, and cut plants back. Gradually introduce plants to indoor conditions before bringing inside to a sunny windowsill. Herbs will put out new growth, but it won’t be as vigorous or as tasty as the summer crop.
September is a good time to begin a compost heap. Begin to layer grass clippings, dried fallen leaves, soil, a handful of fertilizer, and a little moisture. Shredded garden debris can be added as annuals and perennials die back next month.
Pick a dry day this month to test your soil. Plant Information at (847) 835-0972 has listings of soil testing agencies. Follow agency instructions on where and how to collect soil samples. Refrain from adding amendments, fertilizers, or other chemicals to your soil until you know what your soil lacks.
Wait until trees and shrubs drop their leaves or undergo color change before planting them or digging and moving them to new sites. At that time they are entering dormancy and will not suffer as much transplant shock when moved.
Broadleaved and needled evergreens, both dwarf and standard, are best planted or moved by October 1. Water deeply and thoroughly at planting time and each week up until the ground freezes.
Continue to water large trees and shrubs, especially evergreens, until the ground freezes hard. Evergreens continue to lose moisture through their needles throughout winter and must have adequate water in their root zones to avoid winter burn or dessicated needles.
Wait until next month to fertilize any tree or shrub that looks like it might benefit from extra nutrition — for example, has stunted growth, has failed to fully flower or leaf out, or has undersized fruit or off-color foliage.
Winter protection of roses is not necessary until late November, when the ground has frozen.