Assess the Damage
A flower garden can tell you a lot at the end of the growing season. You'll want to assess the results of all your spring and summer work, and prepare the garden for next spring. First, take a walk around your garden and look at how all the plants did over the summer. Track successes and failures of individual plants. Identify which plants have outgrown their space and need to be divided.
Determine which bare areas could use soil amendment and new plants. Add mulch where necessary.
Check for Diseases
Check the overall health of plants — look for diseases and damage.
Replace Old with New
Replace summer annuals in window boxes and garden beds with cool-weather flowers. Dig up any bulb plants that aren't hardy in your zone.
You'll want to weed, deadhead faded blooms, divide overgrown plants, dig up non-hardy bulbs for winter storage, remove spent annuals, amend soil and add needed mulch. Replace ties with jute twine. Natural fibers make the best ties because they're more flexible. They'll break down over time, but at that point, it will be time to retie the plants anyway. Amend soil where there are bare spots or where you've removed annuals. Add compost and peat moss to replace nutrients lost during summer growth and to better prepare the soils for spring planting. Turn the amendments into the soil with a garden fork to distribute it evenly. Brush off any mulch that's sitting on branches of shrubs because it can cause leaves and needles to yellow.
Preparing the Lawn
Within the first six weeks, it will be the ideal time to sow cool-season grasses such as fescue and rye; it will give them the opportunity to germinate and develop a good root system before freezing temperatures arrive.
Fertilizing the Lawn
It's also the right time to fertilize turfgrasses, preferably with slow-release, all-natural fertilizer. When given adequate nutrients, turfgrasses can store food in the form of carbohydrates during the winter months. That will mean a better-looking lawn come spring. This six-week window is also the perfect time to put down a second application of selective, pre-emergent herbicide. The first application — which lawn enthusiasts usually apply in late winter to early spring — takes care of weed seeds that overwintered in the lawn. The second application deals with weed seeds that were deposited during the summer months. At the end of the year, you can also make an application of post-emergent herbicide, or you can spot-treat weeds with a non-selective herbicide such as glyphosate. For spot treatments, you can also use an all-natural formulation such as horticultural vinegar or clove oil. Caution: Know the difference between selective and non-selective herbicides. Selective herbicides target specific weeds or seeds without damaging turf grass or landscape plants in the process. Non-selective herbicides destroy anything and everything green.
Tend to Your Compost
Don't put any diseased plants into your compost pile.
Remove All Annuals From the Garden
You can save seeds from most annuals and plant them next year. Zinnias are an easy plant to collect seeds from and to grow from seed. For window boxes, simply remove summer annuals, add more potting mix and plant cool-weather bloomers like ornamental kale and pansies.
Disinfect pruners before using them on other plants as you remove spent blooms and foliage.
Fall isn't the ideal time to prune roses. Pruning stimulates new growth that may not be able to survive the winter, especially in colder zones. Don't even cut off any dead wood.
Remove faded blooms and dried stems and foliage. This sends energy back into the foliage and roots and encourages new growth. Yarrow flowers can be used fresh or dried in flower arrangements.
Cut faded blossoms. If powdery mildew is present, remove most of the stem that has the worst of the problem. Discard any affected debris — do not compost.
It's important to get these out of the ground before the first killing frost; it doesn't harm the plants to do this while their foliage is still green. Dig out the bulbs and gently shake excess dirt from their roots. Cut off the stalks. Allow bulbs to "cure" (dry) for a couple of days. Put bulbs in a cardboard box with some peat moss and store in a cool, dry place for the winter.
Siberian Iris Care
Dig out the entire clump and then cut it into sections. Replace one section into the original hole and save the remaining sections for other bare areas in the garden.
Cut the vine back to the ground. New shoots will form from the base next spring.
This moisture-loving plant prefers to be divided every three to four years. This will help the plant to continue to grow in the following years.
Coral Bells Care
To divide overgrown plants, dig out the entire clump. Try to keep as much of the root ball intact with as much soil around the root as possible. Cut the clump into sections with a spade.
Completely remove the top growth. Once the foliage has died, you must cut it back to the ground to reduce the risk of plant diseases that are harbored there during winter.
Dividing perennials reinvigorates plants and gives you new plants to add to other areas of your garden or to share with neighbors and friends.
Ready Your Container Plants
Believe it or not, the most overlooked group of plants this time of year is container plants, and there are plenty of things to consider with respect to their care.
By definition, these plants only last a year, but there are ways to extend their lives. You can, for example, take cuttings of various annuals and root the in either water or a potting medium such as vermiculite, perlite or soil-less potting mix. Just remember to strip all but the top few leaves off the stem, keep the potting medium moist at all times and keep plants out of direct sunlight. Within a few weeks the plants should develop a dense mass of roots, at which point you can pot them up and grow them as houseplants. This doesn't work with all annuals, but it's fun to experiment.
Consider transplanting perennials from their containers directly into the garden. Carefully remove them from their pots, trim their roots a bit to stimulate the growth of new feeder roots, stick them in the ground and trim their top growth a little.
They tend to look pretty shabby toward the end of summer, so either harvest and dry them or consider moving them indoors. Generally, though, herbs don't do very well inside unless they get a lot of natural or fluorescent light. (The same goes for most succulents, though cacti seem to fair best among them.)
Keep the Birds Coming
When you invite birds into your yard by feeding them, they do a fantastic job of keeping the insect population in check, which means you don't have to spray or dust as often to control pests.
Don't Forget the Shed!
Take time to clean your garden storage area, tossing old chemicals — responsibly of course — and taking note of what you'll need to replenish before next spring. A number of gardening products have a shelf life and may lose their effectiveness over time or if they get too hot or too cold. That's particularly true of botanical insecticides such as Bt and beneficial fungi. And of course you should tend to your tools. Rub metal tool surfaces with a light coating or oil; rub wooden tool handles with boiled linseed oil; and sharpen everything that needs it with a proper file.