Early Autumn PreparationAs temperatures drop and trees start to change their colors it's a good idea to cut back a bit on your watering. Bushes and trees especially slow their uptake of water and nutrients, and drier conditions help them harden off for winter. Don’t let everything dry out completely, though. They’ll need at least some water in the ground through the winter.
As the lawn slows its growth you may space out the last few mowings a bit. This is a good time to attack perennial weeds before they die back and entrench themselves for spring. Manual removal is easiest at this time of year when the tops are large and easily spotted and grasped. Additionally, many broad-leaved weeds continue growing after the grass has slowed, making them stand out even more.
I’m not a big fan of chemicals and poisons, but this would be a good time to spot spray weeds. Most herbicides require that the plant is actively growing in order to take up the poison, so don’t wait until too late in the year. Additionally, a good feeding for your lawn will provide nutrients that it can use in the spring to get off to a good early start. If you are more organically inclined, finely chopped leaves and other fine organic material can be spread on the lawn to be absorbed throughout the winter.
Do not fertilize your other plants, though. Many bushes and trees can get the wrong signal when given nitrogen and react by putting out new growth, wasting valuable resources that should be stored away, and delaying their preparation for dormancy. Remember that trees pick up water and fertilizer all the way out to the “drip line” below the far ends of their branches.
This is also a good time to get your soil tested. Many ammendments, such as lime for sweetening or sulfur for acidifying require some time in the soil to make a difference in soil pH and bioavailability of nutrients. Modifying your soil in the fall will give you better results in the spring because the ammendments will have all winter to work on your soil.
Late AutumnLater in the season, after the trees have lost their leaves, but before the ground freezes, it is time for a good cleaning. Lawns, gardens, and trees all require room to breathe through the cold winter when their defenses are weakest.
Lawns should be cleared of debris and cut to a reasonably short length. Thatching can also help to remove dead material in the lawn and open up the root zone to allow it to breathe better. In my current desert climate we don’t have much trouble with the lawn through the winter. But when I lived in the wet western peninsula of the state it was important to clear away anything which would harbor fungus and disease. In parts of the country with heavy snowfall it’s also important to remove materials that fungus can grow on under the snow, where air and light can be restricted for long periods of time.
I like to wait as long as possible to clear out the gardens in order to enjoy the last blooms of the season and allow the perennials to slip naturally into dormancy. The California poppies and snapdragons continue blooming for me right through the first snowfalls.
Others prefer to clean out the garden right away to clear away unsightly dead stems and trapped debris that has built up over the growing season. Whenever you clean out your beds, though, be sure to add some mulch over and around the the perennials. The dead material will provide decent protection from the elements until you clear it away. Mulch such as chopped leaves or fine bark will replace some of this protection, both for your plants and for the precious living soil in your beds. I mix in a bit of composted material as well, which filters down into the bed through the winter and helps break down the mulch for use as a soil amendment in the spring. Some people even rototill this material into their vegetable gardens to give them a head start for spring.
In truth, this is the part of the year in which I use the most compost and mulch. Leaves are ideal for this, but be sure to chop them up in a shredder or by running them over with the lawn mower to prevent them from packing down into soggy shingles. The use of compost at this time is more controversial, but I get good results using a mixture of materials next to the ground and pure mulch above. Never use compost in place of mulch, though; it is much too heavy and many of the nutrients you're trying to provide will wash away by spring if they have nothing organic to work on.
Mulch on top of the soil helps prevent winter “heave”--the process of freezing and thawing which can literally wrench plants and roots out of the ground. Organic material worked into the top couple inches around trees and bushes can go a long way toward managing winter moisture by improving drainage while retaining some water to prevent the soil from completely drying out. This organic material will be further decomposed and worked over by bacteria, worms, and other inhabitants of the soil during the winter and early spring to make it available to the trees and plants as soon as they wake up.
Avoid piling mulch directly up against tree trunks where it can trap pathogens against the tree. Grass, weeds, and other material which has piled up around tree trunks should be cleared out as well.
In exposed locations, and where strong winter sun and/or wide swings in temperature are common, it may be wise to wrap the trunks of tender saplings and smooth-barked trees to prevent damage. This is also the time to use dormant sprays on fruit trees and other trees susceptible to early spring insect infestation. Check with your county extension service for appropriate measures for your particular trees in your particular area. Such treatment should be targeted at a particular problem, rather than used indiscriminately as a general preventive, which is rarely effective.
Finally, many gardeners use this time to dig tender bulbs which may not be able to survive the coming winter. My climate (zone 7) is warm enough to maintain most things in the ground if I add a good layer of mulch on top (removing it again in the spring) but I do dig some of the more sensitive tropicals in the fall.
Now, if you’ll excuse me, I need to stop watching the poppies bloom and clean out that front perennial garden before my dear wife starts talking about filling it with red lava rock again.