Harvest herbs in late morning for drying. Wait until the sun has dried up any dew on the leaves, then clip stems, bind with rubber bands, and hang in a dark, airy place to dry. Use a fan to keep air circulating to help minimize problems with mold. Or dry herbs in a food dehydrator or in a warm oven (no higher than 110 degrees F).
Clean Up Garden Debris
As soon as you're done harvesting a row or bed of summer vegetables, take a few minutes to clean up garden debris -- spent plants, fallen leaves, overripe vegetables, etc. Then cover the entire bed with a layer of straw. When temperatures cool a little and rain returns, plant a winter cover crop, such as winter rye or oats, to prevent weeds from taking over. Next spring when you till in this cover crop you'll be adding nutrients and improving soil structure.
Begin digging your potatoes when the tops start to die back. You can leave them in the ground for a while, but the longer they're there, the more susceptible they are to rotting and animal damage. After digging, brush off excess soil and allow the potatoes to dry, then store in a cool (40-degree F), dark room. Inspect stored potatoes frequently for signs of rot.
Keep Weeding Gardens
Although it's tempting to let gardens go after a busy summer of weeding, now's the time to get ahead in preparation for next spring. Continue to weed garden beds frequently. At the very least, remove any weeds that have begun flowering so they don't form seeds. Once you've weeded a bed, cover bare soil with organic mulch, such as straw or shredded bark, to protect the soil and foil future weeds.
Late-Summer Rose Care
Some rose varieties will put out a second flush of blooms in early fall as temperatures cool. Water plants weekly if rain is scarce, and mulch with bark to keep soil moist and cool. Prune back errant canes or those that have been damaged by wind or insects, but leave the heavy pruning until later this fall.