Plant Information
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Smart Gardener
Stand still and close your eyes in the Chicago Botanic Garden’s Dixon Prairie on a warm day in August and you’ll likely hear the hum of countless bees and the chirping of crickets and other insects. You may notice the wind rustle the leaves of tall switchgrass or the sharp “chip” calls of migrating birds as they search for seeds on coneflowers and coreopsis.
August Checklist
Continue to water, weed, and monitor for insects on all garden plants. In times of drought, prolonged hot weather or water restrictions, first water all newly planted trees and shrubs, newly planted perennials and vines, and newly sodded or seeded lawns. Annual plants should be the last on the list, simply because of their ephemeral nature.
Monitor newly planted trees and shrubs for insects or disease. Succulent new growth is often the first area to be attacked by insects. Aphids can be hosed off foliage. Many sucking, piercing, and chewing insects will finish feeding this month, leaving cosmetic damage but nothing serious enough to warrant chemical control.
All gardeners should familiarize themselves with the Asian longhorned beetle — what it looks like, how it damages trees, and how to tell if your tree harbors these fatal pests. Monitor for Japanese beetle damage. These iridescent insects skeletonize foliage but will finish feeding by the second week in August. Favorite host plants include roses and grapevines, and linden, maple, elm, birch, and crabapple trees. They are often found feeding on the tops of plants. If possible, hand-remove them by knocking them into a large jar of soapy water. Hold the jar directly below the feeding beetles. When disturbed, they usually drop straight downward — right into the jar.
Continue to water newly planted trees and shrubs each week if rainfall is insufficient. Watch closely for signs of scorch on tender new foliage — the margins of leaves turn brown and crispy — indicating lack of water and/or exposure to hot drying winds.
Pruning is generally not advised this month, with the exception of shrubs that have just flowered. They are pruned immediately following their flowering.
Roses are generally not fertilized after the first week in August, although growers and rosarians interested in maximizing flower displays do continue to apply a dilute fertilizer.
Continue to deadhead annuals and perennials to encourage additional flowers.
Allow certain dried flowerheads to remain standing for fall and winter interest, including astilbe, coneflower, globe thistle, and others.
Remove yellowed or dried stems and flower stalks of lilies by gently pulling them from the underground bulbs.
Place small stakes in the garden bed where tulips, narcissus, lilies, alliums, and other fall-planted bulbs will go.
Water container gardens as needed. Continue to feed container plants with quarter-strength liquid balanced fertilizer twice a month.
Consider adding to garden beds garden chrysanthemums, asters, or other fall-flowering plants to further extend the flowering season. Many greenhouse-grown mums are not hardy and will not survive over the winter. The earlier the mum is planted in your garden, the greater the chance of survival over winter. Mulch newly planted perennials immediately.
Remove yellowing daylily foliage or leaves that are browned and spotted. Green leaves must remain on the plant to continue to manufacture food. Deadhead individual flowers to keep plants looking tidy.
Daylilies can be divided and replanted or new plants can be installed at the end of this month. Peonies can be planted at the end of this month and into early fall.
Mid- to end of August is the best time to seed bare areas of lawn, overseed thinning grass, or lay down sod. When seeding lawns, use grass seed appropriate to your site. The best choice for most lawns in northern Illinois is a mix of Kentucky blue grass, perennial rye, and fescue seeds. If seeding in a shaded area, purchase a shade-tolerant mix. Cultivate soil down to a few inches and broadcast grass seed and starter fertilizer according to package directions. Cover with loose straw to prevent wind or bird damage to seeds. Keep soil moist until seed germinates.
To overseed an entire lawn, consider hiring a professional or renting a slit-seeding machine that automatically drops seed into small slits made by the machine.
Before laying sod, prepare soil as above. Water deeply to encourage roots to grow downward into new soil bed. Purchase sod grown on soil similar to your own. Let grass grow a bit longer before mowing. Set mower at proper height so that no more than one-third of the grass blades are removed.
Refrain from fertilizing lawns until September.
Annual white grub damage will begin to show up this month as browned-out areas of turf that pull back easily, like a carpet. Grubs chew grass roots, resulting in turf that lifts up. Minor damage is usually not cause for treatment. Pull back turf and count grubs (white C-shaped larvae with black heads); 10 to 12 per square foot is considered enough to treat. Recommended chemical products vary in their application time. Many gardeners wait until the third week of the following June to apply imidacloprid. If possible, try to avoid using strong insecticides if damage is light. If necessary, treat affected areas rather than entire lawn.
Homeowners might notice a chewed-up appearance to their lawns if grubs are numerous. Skunks, raccoons, and birds will tear up grass searching for grubs, especially at night, sometimes doing more damage than the grubs themselves.
In times of drought, excessive heat, or water restrictions, grass can go dormant. The grass will turn yellow but the crown of the plants will remain alive with just a half-inch of water over several weeks. Grass will green up as soon as normal rainfall returns.
During the first week of August, plant short-season snap beans, broccoli, cabbages, cauliflower, carrots, mustard greens, spinach, and radishes for fall harvesting.
Cool-season lettuces, mesclun mixes, and unusual greens that were planted in early spring can be planted again this month. If weather is unusually hot, plant these greens in partial shade.
The best quality and best tasting salad greens come from plants that were watered frequently and lightly rather than infrequently but deeply. This advice is the exact opposite to what is recommended for watering trees, shrubs, perennials, grass, and other plants.
When harvesting lettuces, cut every other plant to the ground. This practice allows each lettuce head to develop fully.
In hot weather, lettuces and cabbages can bolt quickly and form seed stalks. These stalks render the leaves bitter. Remove any stalks as soon as they begin to grow.
When buds form on Brussels sprouts, remove the lower leaves. Taller plants with more sprouts will result. Sidedress plants with balanced fertilizer when sprouts are marble-sized.
Keep vegetables picked so the plants will keep producing.
Avoid letting squashes, zucchini, etc., become giant-sized. They may win county fair prizes, but they will have little flavor.
Monitor for blossom end rot on tomatoes. Tomatoes are very moisture-sensitive. Mulch garden beds and keep moisture evenly available for these plants. They don’t grow well when exposed to cycle of rain, drought, rain, drought.
Keep records of harvest dates to help plan next year’s garden.
Continue to harvest herbs by either snipping foliage, drying entire sprigs or plants, or freezing individual portions in ice-cube trays. Pinch off developing flowers to retain essential oils and flavor in the plants’ foliage.
Herb plants that can be brought inside for a windowsill garden will be dug and transplanted next month.
Continue to monitor edible crops for disease or insect problems. Avoid spraying strong insecticides or fungicides on food products.
Hand removal of caterpillars is recommended.
If hot, dry weather persists, some fruit trees might abort their crop. Apple trees require deep watering for maximum fruit production.