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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.
Plants brought indoors this fall might exhibit temporary “transplant shock” in their new environment due to changes in light and temperature. Sun-loving houseplants might suffer during cloudy winter season. If possible, consider supplemental artificial lights. Avoid overwatering houseplants. Cut back on fertilizer in general, except for plants intended to bloom all winter, such as miniature roses or geraniums.
Most houseplants appreciate a 10- to 15-degree difference in day and night temperature. Monitor plants for early signs of problems. When indoor heat is turned on, natural humidity disappears. Try to wash plants occasionally in a warm shower. Humidifiers and pebble trays can help raise humidity.
Pot up pretreated bulbs, such as amaryllis, paperwhite narcissus, and others, for holiday blooms.
Extra hardy bulbs not planted outside this month can be potted up and forced for indoor blooming. Plant bulbs in wide, shallow pots in a soilless mix. Large bulbs are planted side by side with just their tips showing. Little bulbs are planted with ½ inch of mix covering them. Water well and place pots in a refrigerator, cold frame, garage, or shed where the temperature remains between 35 and 40 degrees Fahrenheit. If storing in a refrigerator, cover pots with plastic wrap and avoid storing ripening fruit in same area. Some fruit releases ethylene gas, which inhibits flower formation. Major bulbs require 12 to 14 weeks of cold storage; little bulbs require a few weeks less. When pale yellow sprouts begin to show, pots can be brought out of cold storage into a bright but quite cool room (55 to 65 degrees F.) for about two weeks. As flower buds begin to develop, bring pots into a warmer room but avoid direct sunlight. Water as needed.
Watch weather conditions for an appropriate window of time to spray fruit trees or large deciduous trees with dormant oil. Spray if aphids, scale, or mites were a problem in the past. Temperatures must be at least 40 degrees Fahrenheit with no chance of freezing or rain within the following 24 hours. Avoid spraying on a windy day. Certain trees have a phototoxicity to dormant oil and should not be sprayed. A few common ones are arborvitae, beech, red maple, Japanese maple, sugar maple smokebush, blue spruce, blue cultivars of juniper, and yew. Call Plant Information if in doubt.
To reduce the spread of oak wilt, all oak pruning should be completed in March, or before the oaks begin active growth. Pruning should not resume until after the first frost, or around November 1.
Prune fruit trees in early March on a dry day before buds swell. As with all pruning chores, sterilize pruning tools with a 10 percent solution of bleach before each cut. Prune out sucker growth, water sprouts, and any diseased or dead branches. Remove crossing branches, rubbing branches, or those that grow toward the center or the plant rather than outward, away from the interior. Fruit trees benefit from having their canopies opened up to permit more sunlight and air into their centers.
Prune spring-flowering trees and shrubs immediately after they flower to preserve this season’s flower display.
Prune roses when the forsythia begins to bloom. When pruning roses, make a 45-degree cut above a healthy bud, angled away from the center of the plant. If not done last fall, prune hybrid tea roses and grandiflora roses back to 12 inches to reinvigorate growth. Prune out dried, darkened, and broken canes and any dead tips. Prune shrub roses to remove dead wood and very lightly to shape to size.
Fertilize woody plants four to six weeks before they begin new growth only if they have shown signs that they could use it. These would include poor leaf color, failure to completely fruit or flower, or stunted growth. Use a slow-release granular fertilizer or an organic product and water in well. Do not fertilize newly planted trees or shrubs. Wait one year before making this application.
Plant trees and shrubs before they break bud and when soil conditions permit. If spring weather is unusually wet, consider planting in the fall when the plants begin their dormancy. With all woody plants, avoid planting too deep. Research indicates that more trees suffer from being planted too deep in the hole than any other problem. Plant with one-third of the root ball above ground. Taper soil away from the trunk back to ground level. Mulch the entire root zone with several inches of shredded or chipped bark.