Have a question? Contact Plant Information Service.
Use the search box below to search plant information. Or choose a month from the drop down menu to view monthly garden checklists.
The polar vortex and a very wet, cold spring delivered a knockout punch to some plants this year. (You may recall that the Garden was closed for two consecutive days in late January due to extreme weather conditions.) Japanese maples and boxwood were hard hit across northeastern Illinois. Two sycamore trees in the Sensory Garden developed dramatic frost cracks.
Newly planted trees, shrubs, perennials, and roses must receive 1 inch of water per week throughout their root zones. This is especially important in hot, dry weather.
Continue to cultivate and weed. The return of hot weather will certainly push weed growth.
If not done yet, mulch garden beds immediately after weeding with 2 to 4 inches of shredded bark. This is the best way to retain moisture and keep weeds under control.
If not done yet, renovate overgrown shrubs including redtwig dogwood, lilac, and forsythia by removing one-third of the oldest canes.
Prune out all ground-level sucker growth from crabapple, apple, plum, peach or apricot trees by cutting out growth below soil level.
Prune out weak, green but very fast-growing water sprouts that grow vertically from branches of fruit trees, redbuds, or other ornamental flowering trees.
If necessary, boxwood and yews can be lightly pruned to maintain geometric form. Avoid overpruning, especially in very sunny, hot weather.
Fertilize roses for the third and final time at the end of the month with a liquid 20-20-20 fertilizer. Do not fertilize after August 1.
Continue to deadhead roses by cutting flowers back to the first set of five leaflets.
Monitor roses closely for blackspot. Remove any leaves that show darkened circles with fuzzy margins on either the topside or underside of leaves; yellow foliage with dark spots; and any leaves that have already dropped from the plant. Begin a spray program with approved fungicides immediately. Always choose disease-resistant roses in the future.
To promote a second, late-summer flower show, cut back, shear, or remove flower spikes from the following early blooming perennials: catmint, geraniums, salvia, and delphiniums.
Annuals in containers and hanging baskets may require daily watering during hot or windy weather. Continue to fertilize container plants with half-strength balanced liquid, but avoid applying in the heat of the day or during long, hot dry spells. Always water plants before fertilizing.
Remove spent flowers or seedheads of daylilies immediately to conserve plant energy.
Monitor foliage of densely planted annuals and perennials that might show fungal attacks due to cool, damp weather earlier this season.
Continue to pinch out new growth of tall sedums, asters, and chrysanthemums until the middle of the month.
Stake tall plants, if necessary, by tying with soft nylon ties.
Continue to guide clematis vines and all other soft-stemmed vines to their supports.
Make note of empty spots in borders that might benefit from planting summer-flowering bulbs next year.
Seeds of perennials can be sown directly into the garden at this time. Note their location to avoid accidental "weeding" next spring.
If necessary, dig and divide Oriental poppies as their foliage yellows and dries. Always plant poppies in sunny, well-drained areas. Avoid moving them, if possible. Since poppies fade out by midsummer, plant annuals or later-blooming perennials in front of them to conceal their unattractive yellowing foliage.
The lush greenery that grew abundantly during a rainy spring might become a target for insects. Monitor closely but avoid drastic action or strong chemicals until insects are correctly identified. Many, like aphids, will go away with a strong stream of water from a hose. Aphids have many natural enemies and are rarely cause for harsh pesticides. When in doubt, visit Plant Information at the Chicago Botanic Garden.
Do not fertilize lawns in summer. Early fall is the best time to apply a 3-1-2 ratio fertilizer.
During drought or times of water conservation, turf will go dormant, but the grass plants’ crowns will remain alive with only 1 inch of water.
Mow grass at a high level in hot summer, 2½ to 3 inches. Grass clippings can be left on the lawn and gently raked to avoid clumping.
Avoid using herbicides in hot weather. Always read directions carefully. Pull out annual weeds, such as crabgrass, before they go to seed.
Continue to harvest herbs to use fresh, and dry or freeze them in small batches in an ice cube tray. Pinch off developing flowers to retain essential oils and flavor in the plants’ foliage.
Monitor tomatoes during hot weather. Tomatoes appreciate an even supply of moisture rather than a heavy soaking and then a drought. Straw mulch is helpful in these beds.
Many hot-weather-loving veggies, such as peppers, tomatoes, eggplants, and cucumbers, might be delayed in fruit production due to a cool, wet spring. Side-dress these vegetables with a nitrogen fertilizer, taking care not to spread it on the plants’ foliage. Water in well.
Monitor vegetables for symptoms of fungus or blight: soft, darkened areas; yellow and dropping leaves; or sunken dark spots on otherwise green foliage.
Harvest onions and garlic as they are ready, and begin the drying process.
Seeds for fall crops may be sown toward the end of the month. These include beans, broccoli, spinach, cool-season lettuce crops, and cabbages.
Monitor all plants for insects. The return of sunny, hot weather will bring a bumper crop of insects. Hand-remove large insects such as tomato hornworms and other caterpillars.
Caterpillars on fennel, dill, and carrots might likely be those of swallowtail butterflies, which lay their eggs on these favorite host plants. Consider planting a special herb crop just for them next year.
Monitor apples during late July when apple maggots are laying their eggs. Visit Plant Information for current control methods. Some gardeners place red decoy apples in trees to trap these pests. When the insect count reaches a high level, control steps are then taken.
Espaliered fruit trees should be pruned for the second time once their spring flush of growth is over. The first pruning is done in late winter when plants are dormant.