Sow new crops of beets, carrots, and summer lettuce to extend the harvest. You don't need much space, you can sow a border around other vegetables. If possible, choose a spot that's partially shaded by taller plants for sowing lettuce, so it will stay cooler.
Tomatoes, squash, and cucumbers can use some nutrients now, so scratch some granular fertilizer into the soil around plants or in a shallow trench alongside a row. Do this when the soil is already moist, and then water it in.
Patrol for Japanese Beetles
Begin the early-morning or early-evening patrols for Japanese beetles and knock them into a can of soapy water. You can also hold a bucket under a plant that's hosting a beetle party and gently shake a branch and the beetles will fall into the bucket. Forget trying to catch them midday because they move too fast in the heat.
Adopt a Weeding Strategy
If you've gotten behind in weeding, start going after the ones in flower first, to prevent their seed from spreading. Then tackle the tallest ones before they overpower your plants. Save the low spreaders for last. Since weeds are only trying to prevent bare soil, spread mulch as soon as the weeds are out of the way.
Prune Shrubby Perennials
Cut back shrubby perennials, such as catmint and dianthus and veronica, when they finish blooming. This will tidy them up and encourage them to produce a second flush of flowers.