The landscape around us is obviously winding down as the days grow colder and the nights get longer. Mid-to-late fall sees most of the plant world going from mellow to muted to moribund. But, contrary though it seems, this is the best time of the year to plant new things and to work in the garden.
The reason is simply fall weather, which, up until the ground freezes, is kind to human beings as well as to newly planted trees, shrubs, and perennial plants.
In autumn, there are many more good days to be outside than there are in spring. Serious gardeners love November; they're happy working up a sweat inside their hoodies and gloves when everyone else is starting to huddle indoors. The season fits the typical gardener's temperament—moody, melancholy, prepared for doom, and happily surprised when something does well. (This was typical among my gardener colleagues at the New York City Parks Department. But that may have just been a result of the city stressors.)
At first thought, spring, with its explosion of buds and shoots and sprouts seems like the best time to put new plants in the ground. But spring in much of North America has quite a small window for planting—between the last frost and the onset of hot weather. Some of the days in that window will be rainy, making the soil muddy and hard to work with a lot of the time. The soil takes a while to warm up from a winter's worth of cold; a new plant's roots grow slowly in chilled earth.
In fall, the soil still holds summer's warmth, which encourages root growth up until the ground freezes. Fall planting gets perennials, shrubs, and trees off to a faster start the following spring. In mild-winter parts of the country, fall is even more emphatically the superior season for planting because roots can keep growing all winter.
Plants shift their objectives when the sun wanes and the temperatures go down. They stop the spring and summer work of making leaves, shoots, flowers, berries, and fruit. All their energy goes into establishing roots.
Trees, shrubs, and perennials put into the ground in fall don't have to deal with heat and drought early in their young lives. By late next spring, when things begin to heat up, the plant's roots will be up to the job of absorbing and circulating nutrients and water. The class of October 2008, in other words, will be better equipped next summer than their brethren freshly planted in April 2009.
If these climate factors aren't enough, consider that fall planting can save you money. Many nurseries mark their perennials and shrubs 20 percent off in the fall. They'd like to unload plants so they don't have to water them through the winter.
A couple of cautionary notes: When you walk the garden center aisles, the perennials may look sad. Remember that their life force is in the roots and crown—the place where the base of the leaves meets the roots. This time of year, you don't want a lot of leaves. Look at the picture on the plant label and have hope.