Water, water, water! Lawn and flowers need about 1 inch of water a week to stay green and healthy. Use a rain gauge to make sure they're getting enough. If using a sprinkler, set out a pan or tuna can on the lawn to measure how much water falls. (Best time to water: early morning. It prevents evaporation and allows foliage to dry quickly to prevent disease.)
Weed, weed, weed! When the weather is hot, it's easy to avoid getting out in the garden. But work in the cool of morning or evening so the weeds don't take over.
Top off beds and other plantings with more mulch, if you want. It slows the return of weeds, conserves moisture, and prevents soil-borne diseases from spreading. Just remember: Mulch should be 1 to 3 inches deep, no deeper.
Start thinking about structural projects you might want to tackle this fall. Plan a path or an arbor that you want to build when the weather cools.
Water containers often. In hot weather, they usually need watering daily and may even need watering twice a day -- especially thirsty plants such as fuchsia, impatiens and hibiscus. If the container soil dries out and gets so hard that water runs rapidly down the inside surface of the pot, set the pot in a bowl or bucket of water halfway up the container's sides. After a couple of hours, the soil will rehydrate.
Every time you water container plants, pinch off yellowing or problem foliage and spent flower blooms to encourage more lush growth and flowers.
Fertilize containers every two weeks to assure plenty of growth and bloom. Use a bloom-booster fertilizer with flowering plants.
Petunias getting ratty-looking? It's a good idea to cut all your annuals back by one- to two-thirds to encourage fuller, bushier growth with more flowers. In Zones 3-5, if your cool-season annuals such as snapdragons and lobelia have made it through summer's heat (they often die out in July and August), cut them back by about half to encourage a fresh flush of growth and bloom in the cooler temperatures of fall.
Deadhead flowers regularly. Deadheading not only keeps your landscape tidy-looking, it also encourages certain flowers to bloom more.
Tackle diseased plant areas. If the plant is an annual and badly damaged, consider just tearing it out. This time of year, it's not likely to recover and will only look bad and possibly spread the problem to its neighbors. Otherwise, trim off an affected part of the plant and take it to a quality local garden center. They'll be able to diagnose the problem and recommend a solution.
In Zones 4-6, stop fertilizing roses and any other trees and shrubs. Fertilization will encourage new, tender growth that will get zapped by winter cold.
Mow high this time of year. Longer grass will shade the soil, conserving moisture and discouraging weeds. Mow 3 inches high for cool-season grasses such as Kentucky bluegrass and 2 inches for most warm-season grasses, such as Bermudagrass and zoysia. But don't let your lawn grow too high before you mow - the rule of thumb is never to remove more than one-third of the grass blade at a time, or you'll stress your grass.
Keep vegetables harvested. Harvesting encourages vegetables to keep producing well until fall. This is especially true with green beans, but also with green peppers, hot peppers, cucumbers, squash, eggplants and tomatoes.
In Zones 3-4, in late August or in early September, plant cool-season veggie crops such as lettuces, spinaches and radishes. Be sure to keep them moist.
Set tuna cans, wire racks or other supports under small ripening melons to prevent them from rotting or attracting slugs from contact with the soil. Harvest cantaloupes after they turn from green to yellow and come off the vine with a gentle tug. Pick watermelons when they have a dark and crisp stem, shriveled tendrils close to the melon and a dull look with yellowish underside. Ripe watermelons also produce a dull thud when thumped.