August and September Gardening Guide

Fall is in the air! As Nathaniel Hawthorne wrote, “I cannot endure to waste anything as precious as autumn sunshine by staying in the house.” Here’s hoping this list of things to do outside during late August and September helps you stay outside profitably!

Warm season grasses to fill in bare areas. Planting in August – September allows enough time for grass to establish roots before cold weather. Water frequently, keeping grass moist until roots are solidly attached to the soil. See Aggie Turf for information on establishing and caring for
Fall is a wonderful time for planting perennials. Keep soil moist until temperatures return to the low 90s.
You can plant any perennial herbs now, including dill, fennel, parsley, cilantro, thyme, oregano and rosemary. Spread wildflower seeds in a cleared bed for spring blooms.
Rejuvenate old perennials by dividing them. If your older perennials aren’t flowering like they used to, it is probably time for them to be divided by dividing the root system of one large plant into two or more sections that can then be replanted. Perennials like daylily, daisies, coneflower and iris do best when divided every three years. Replant them in your own garden or give some to friends.
Plant trees and shrubs. Beginning in September and moving into October and November is the preferred time to plant all trees and shrubs. Just like perennials, trees and shrubs that are planted in the fall will have the winter months to establish a deep root system. Their spring growth and drought resistance will be much better than if you plant them in the warmer months.
Plant leaf lettuce and other cool season vegetable crops, such as broccoli, cauliflower and cabbage transplants as well as seeds for root crops, like beets and carrots, can be planted now. Provide shade cover while the plants adjust and place mulch on top of the soil to retain moisture. See Aggie Horticulture Fall Planting Guide.
Plant garlic now for a flavorful harvest next summer. Garlic is very easy to grow. Simply plant individual cloves 2 inches deep in your vegetable garden or in a container. Plant each clove with the pointed end up, 6 inches away from each other in rows that are 1 foot apart.
Plant color annuals that will withstand light frosts in pots to highlight doorways and patios. You can break off healthy shoots of annuals such as coleus and geraniums and root them in water or starter mix. Protect them indoors through winter. Replant in spring.
Start a wildflower garden. You’ll have until Thanksgiving to plant seeds, but the first part of September until early October is the best time. Bluebonnets, Indian paintbrush, Indian Blanket, and winecup require full sun and well-drained soil to flower best.
Dry herbs. Herbs can easily be dried by tying them in bunches and hanging them in a dry, dark area. Drying takes a few weeks. Once the herbs are dry, crumble the dried leaves into small pieces, store them in sealed jars. Fresh herbs can also be frozen in ice cube trays using olive oil or water, then placed in a baggie to use
Remove dead branches from trees and shrubs. Continue to prune hedges lightly. Remember to taper shrubs so that the base is slightly wider than the top.
Prune summer annuals that have become leggy. This includes lantanas, zinnias, coleus and firebush.
Stake and tie leggy vegetables before they flop over and bend their stems. Build supports to keep the branches and fruit off the ground.
Add organic material to your vegetable garden to replace what has decomposed during the summer heat.
Fertilize VERY LIGHTLY clumps of established warm-weather, small-flowered landscape plants, such as narcissus. Late summer fertilizing can stimulate an excessive amount of new growth, making plants more susceptible to winter injury.
Watch For:
Mosquitoes – Change animal water sources daily to decrease possible mosquito attacks. Link to the Earth-Wise Guide to Mosquitos here.
Spider mites like hot dry weather. They are tiny and may go unnoticed until leaves become discolored or the webbing becomes apparent. Spider mites can be found on vegetables like beans, cucumbers, eggplants, melons, peppers, pumpkins, squash, tomatoes and zucchini as well as annuals like impatiens, geraniums, zinnias. Spray the undersides of the leaves (where they congregate) with cold water. The next line is insecticidal soap. Link to the Earth-Wise Guide to Spider Mites here.
Grubs – The best time to eliminate grubs is around Independence Day, but if you didn’t do it then, do it now while they are tiny and can be killed with small amounts of chemical. Don’t wait until next June when you see giant grubs! Learn more about grubs here.
Powdery mildew on Crepe Myrtles and Roses. Learn control and prevention measures here.
Aphids – Keep your eye out for aphids on your veggies, fruit trees and other woody plants. The hot weather shortens the time needed for eggs to hatch and become reproductive adults. Use a strong stream of water to knock them off plants or use an insecticidal soap spray. Link to Earth-Wise Guide to Aphids
Whiteflies – can attack many plants but seem to favor squash, tomatoes, peppers and eggplants. There are many natural controls already in your garden like ladybugs and parasitic wasps. Use a shop vac and a long extension cord, then shake the leaves and suck up those fast moving sap suckers. You can also control the wingless nymphs with insecticidal soap, horticultural oil (summer oil) or neem oil.
Black Spot – Roses may show signs of this fungal disease. First line of defense is keeping water off the leaves and growing plants in areas with good air circulation. Avoid overhead spraying of susceptible plants. Another first line is removing all infected leaves that appear. You can also spray with an appropriate fungicide like Rose 3-in-1 (neem oil) weekly into the fall
Fall web worms forming webs at the end of branches. Remove twigs and place in closed plastic bags for trash pickup.
General Landscaping
Plants need less water as the temperatures cool, so adjust your irrigation controller as needed.
Apply pre-emergent weed killer to your lawn early in the month to keep winter weeds from growing in your dormant turf.
Add organic material to your vegetable garden to replace what has decomposed during the summer heat.
Add 2 to 4 inches of mulch to beds, if prior applications have decomposed and left thin or bare spots.
Gauge your water usage! Grasses slow down in high temperatures, so you may be watering plenty, the grass is just resting.
Keep the compost pile turning. Add additional organic matter and turn the compost pile to aerate it and encourage aerobic bacteria to become active.