Gardening by Month - September

Trees & Shrubs

• Trees and shrubs can be planted for fall now through November. Be sure to adequately water new plantings.

• Magnolia scale young crawlers are hatching now, control is most effective at this time. 

• Seasonal loss of inner needles on conifers is normal at this time. It may be especially noticeable on pines and arborvitae.

• Spruce spider mites may be present as the season cools.

• Spruces infected with Rhizosphaera needlecast should have infected branches pruned out and any fallen needles cleaned up. 

Annuals & Perennials

• Perennials, especially spring bloomers like peonies, can be divided now. When planting peonies plant only 1-2 inches deep, as planting too deep can cause flowers not to form.

• As milkweeds (Asclepias sp.) form pods, milkweed bugs can be found eating the seeds, leaves, and stems. Damage is minimal and most infestations are merely a nuisance.

• Cuttings of annuals can be taken now to provide vigorous plants for overwintering.

Lawns

• Reseed dead spots in the lawn as needed.

• Cool-season lawns can now be fertilized. Between September and December, up to 3 applications of fertilizer can be made. Do not exceed rates recommended by the fertilizer manufacturer.

• Thoroughly water lawns as needed.

• Cool-season weeds may be showing up; manually remove or use a proper herbicide as needed. Annual weeds can be controlled using an application of pre-emergent. 

• Begin fall seeding or sodding of cool-season grasses. Seedbeds should be raked, dethatched, or core-aerated, followed by fertilizing and seeding. Keep newly planted lawns moist but not wet. 

• Do not mow newly planted lawns until they are 2-3 inches tall. 

• Fairy rings and mushrooms may appear in lawns after rain, no control is needed as little to no damage is done to grass. Manually remove mushrooms and treat them as yard waste.

Fruits & Vegetables

• Pick pears before they are fully mature. Store in a cool, dark basement to ripen.

• Clean up any fallen or spoiled fruits.

• Pawpaws (Asimina triloba) are ripening now.

• Check all along peach tree trunks to just below the soil line for gummy masses caused by peach tree borers. Probe holes with thin wire to puncture borers.

• Harvest summer herbs now and process them for winter use.

• Pinch off young summer fruits (tomatoes, peppers, squash, etc.) to promote ripening of more mature fruit. 

• Finish planting cool-season seeds like leafy greens and radishes by mid-September. Sow seeds of these crops in a cold frame or low tunnel to prolong fall harvest.

• Cabbage loopers and imported cabbage worms may be present as more cole crops are planted and temperatures cool.

Miscellaneous

• Autumn is a good time to add compost to garden soils to increase organic matter content.

• Monitor plants for spider mites. Hose off with a strong stream of water.

• Start to prepare houseplants and other tropical plants for overwintering indoors. Check for pests and treat them appropriately. Houseplants and tropical plants need to be brought in as night temperatures reach the low to mid-50s.

• Whitefly populations are often the highest at the end of summer.

• Monarchs are migrating now; it's normal for milkweed plants (Asclepias sp.) to appear depleted due to caterpillar feeding. 

• As fall progresses, box-elder and red-shouldered bugs start to search for overwintering sites, including homes/buildings.

• Garden spiders may be more noticeable this month, especially webs found on boxwoods. Spiders are natural predators for many garden insect pests.

• Damage from scorch, sunburn, and heat stress from the summer may be noticeable. In subsequent years, be sure to provide enough water to plants early in the day on hot days.