Make Notes for Next Year
While problems with this year's garden are fresh in your mind, jot them down somewhere. Note where plants have become overcrowded to help you remember what needs to be moved where next spring. Note any sun-loving plants that are now too shaded, and spots where water puddles that need to be amended to improve drainage. Or if visuals are more helpful, take photos of problem areas and write notes on the back of them so you'll know where to start with redo's next spring.
Take Annual Cuttings
Take cuttings of favorite geraniums, coleus, begonias, and any other annual flowers that you want to overwinter for replanting next year. You can also bring these plants indoors for the winter if you have a sunny spot. Several popular bedding plants are perennial in warm climates and can be brought indoors as houseplants if you don't wait until the weather gets too cool. Cold temperatures can set them back and make it hard for them to recover. Gradually move the plants into shadier locations so they are better adjusted to the reduced light levels when you move them indoors.
Sow Cover Crops
As you remove spent plants from your garden beds, sow a cover crop, such as winter rye. This will help reduce weed infestation, minimize erosion and compaction from fall rains, and will add nutrients and organic matter to the soil when it is tilled under next spring. If you're making a new bed, it's also a good idea to build the soil with a cover crop for a year before planting. Till in the cover crop before it goes to seed, either later this fall or early next spring.
Refresh Container Plantings
If you return from vacation to find tired plantings, you have two choices: cut them back and fertilize and hope they rejuvenate in time for you to enjoy them; or toss them and start anew (giving up is not an option yet!). You can still find annuals at garden centers, or pot up some blooming perennials that you can plant in the ground later in the fall. Or consider a combination of foliage plants, such as coleus, that you can bring indoors for the winter.
Keep Watering Newly Planted Trees and Shrubs
Woody plants that you put in this spring or summer need adequate watering for the first year. Even when it rains, the moisture might not soak deeply enough to reach the roots and encourage them to spread. The best way to apply water is to lay your hose at the base of the plant and let it drip for an hour or more. Then gently dig down to see how deep and far the water penetrated. You'll probably need to move the hose around to reach all around the dripline. A soaker hose makes this easy because you can lay it in a ring around the plant to water all sides evenly.