The heat and common foliar diseases of summer can take their tomato plants. However, you may be able to get a new flush of growth -- and fruit -- by pruning the plants back by about half and fertilizing them. If the roots are still healthy, you should see a strong flush of new growth.
The extreme heat takes its toll on plants. Keep plants watered, but water wisely. Give established plants a good soaking about once a week, rather than sprinking them lightly every day. You'll encourage plants to develop deep root systems that are less prone to drying out, and you'll minimize foliar disease problems. New plantings, seedlings, and container-grown plants will need more frequent watering.
Sow Fall Beans and Cukes
There's still time for a last crop of bush beans and cucumbers. Look for the fastest-maturing varieties you can find -- remember that vegetables grown in fall need about 14 extra days to mature compared with spring-seeded crops due to fall's shorter days and less intense sunshine.
Despite the heat, late summer is the best time to dig, divide, and replant bearded iris. If your iris stands are getting crowded, often evidenced by reduced flowering, it's time to divide. Cut the foliage back to 4-inch fans to make them easier to handle. Divide the roots, making sure each division has one or two leaf fans. Older rhizomes that have few white feeding roots should be discarded, as should any with small holes that indicate the presence of borers. Expect reduced flowering the first season after replanting, followed by a strong comeback the following year.
Cut Back Herbs
Trim back mint, thyme, oregano, and other perennial culinary herbs. More branches will emerge, keeping the plants bushy and full. Use the clippings fresh or freeze them for later use. If you haven't done so already, harvest basil by cutting branches back by half or more; you'll get lots of new growth for a second batch of pesto.