The benefits of autumn planting.

All things green.
Sept. 22 2008 6:45 AM

"Autumn Is a Second Spring"

The advantages of planting a garden in the fall.

Fall gardening. Click image to expand.
Fall gardening

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.

Look for container-grown, or balled and burlapped, shrubs and trees. For all the season's benefits, fall is not a good time to dig trees out of a field where their roots have sprawled and would have to be trimmed back.

If you garden in a cold-winter area, it's better to wait till spring to plant shrubs or perennials that are marginal—things like buddleia or caryopteris.

Fall transplanting means using less water. It's cooler, and the plants are less thirsty while they're going dormant. But those recently planted shrubs and perennials and trees do need a deep, thorough soaking at planting time; and when there's no snow cover, water every four weeks or so through the winter.

Here's the most important caution. You may want to give your new plants a little artificial assistance in the form of fertilizer. Don't give them a fertilizer that is high in nitrogen, which would encourage succulent, green, springlike growth at a time when you, and the plant, want dormancy.

For immediate cheer, remember that anywhere but in the most tropical parts of the country you can put in pansies. A newly bred super race of the velvety flower, with names like "Snowman" and "Icicle," has just hit the market. In horticulture labs, scientists have intensified pansies' natural cold tolerance. (They're related to wild violets, which developed a sort of antifreeze in order to survive the cold on the deeply shady forest floor.) These new pansies will bloom now, sit tight under the snow, and pop back to bloom again in spring. Not surprisingly, they hate heat, and you'll probably have to compost them next spring.

Even if you don't feel like buying anything new, fall is a good time for cathartic, satisfyingly destructive garden activities. Leave echinacea, sunflowers, and cosmos to go to seed and feed the birds, but tear up annuals like impatiens, marigolds, petunias, zinnias, and tomato plants. If you're not ready to start a compost pile, here's an alternative that requires high aerobic output (and saves on plastic garbage bags): Dig a trench in your vegetable plot. Pile in the tomato stalks and shriveled pepper plants and blackened basil plants, etc. Cover with earth, and next spring you will have Worm City and good soil.

Since we've gotten candidates from Hawaii and Alaska, I've been enjoying the sound of the phrase "the noncontiguous United States." It turns out that even in Alaska, fall is a good time to plant. It's true that by Halloween Anchorage usually has snow on the ground. But up until then, as long as the ground isn't frozen, Alaskans should be digging.

For residents of everywhere else: Even if you've never done a thing in your garden, plant some spring bulbs. You can do this late; it's actually best to plant bulbs after a killing frost. Their only demand is a sunny spot and well-drained soil.

One more note on composting: When wild tulips first came to Western Europe from Turkey in 1562, the burghers of Antwerp, who saw them as onionish, tried to eat them. Not surprisingly, they didn't like them and had their servants toss the extra bulbs onto a pile of organic refuse. The bulbs rooted themselves in the muck and flowered—another tribute to the generative powers of compost heaps. A few centuries later, the Dutch, including a young Audrey Hepburn, would eat them during the days of the Nazi occupation of the Netherlands.

Constance Casey is a former New York City Department of Parks gardener and writes the monthly "Species" column for Landscape Architecture Magazine.