TREES & SHRUBS: Water: deeply about once a week. Prune only dead and damaged branches, or the ones that are in bad places. Dr. Reed calls this "head pruning" - taking out the ones that you hit your head on while mowing the yard. Watch for caterpillars, which are best controlled before they do too much damage. Aphids (and the sooty mold which grows on the honeydew they drop) are also common right now, especially on smaller trees, shrubs, fruit trees, and perennials. Treating for the aphids will usually help with the mold.
FLOWERS: Plant new heat-tolerant color, such as lantana, verbena, vinca, pentas, purslane/moss rose, sweet potato vines, coleus, salvias, hibiscus, etc. Trim up & fertilize any older plants from spring that are looking shabby. Watch for aphids & sooty mold, lace bugs, caterpillars, snails & slugs.
VEGETABLES: In our climate, there are 3 ways to garden in the second half of the year.
1. Revive heat-tolerant warm season veggies that made it through the summer: Trim a bit, fertilize, and water evenly and often. Watch for those aphids and other mean critters. Talk to the plants nicely, commiserate with them about this insufferable August heat, and hopefully (usually) they'll show their appreciation with another round of production.
2. Plant the next succession of warm season veggies: NEW TRANSPLANTS (TOMATO, pepper, etc) & NEW SEEDS (pumpkins, squash, snap/green beans, bush limas, peas, okra). Fall seed potatoes can be planted, typically from leftover potatoes from spring.
----> Note: The sooner you plant, the more likely you'll harvest before the first frost. The more quickly maturing (ie small-sized) the variety, the more likely you'll harvest. If the first frost is late, the bigger, slower varieties and the later-planted sets CAN produce well, but it's a gamble. You could say, it's better late than never unless you have contrary weather.
3. Vegetables started in the fall for harvest in winter or spring: Think cool-season crops: cole crops like broccoli, leafy greens like lettuce, root crops like carrot and onion. While it's too early to plant these, you can scope out seeds and plan their respective places in the garden. That way, when the time comes as the weather cools a bit, you'll be ready to go.
Good luck, gardeners! And wish me a little -- I'll be dividing and transporting a few of my precious Pawpaw's Louisiana daylilies (yes, even though it's entirely too hot to do so) from my Texas garden to my cousin's Colorado garden later this month. Fingers crossed they make it!