by Jack Ruttle
In most American yards, fall is a time when gardening activity winds down. It's the time to clean the place up and put the garden to bed. Planting, with the exception of spring bulbs, is the furthest thing from most people's minds. But the truth is, fall is an ideal time to plant nearly anything - perennials, shrubs or trees - in any area where the ground remains unfrozen for a month or more after the first killing frost. Whether you're planting new stock or digging up existing plants to rearrange the landscape, this is the time to do it.
The reason has to do with roots. When a plant is put in the ground, most of its roots die. Before the plant can regain its former vigor, it needs to replace those roots. But in spring, a plant wants to produce a lot of new shoots and leaves instead, so that it can flower and reproduce. Roots will regrow then, but slowly In late summer and early fall, on the other hand, as the plant is shutting down its leaf growth and stem extension, it's expanding its root system. Below the soil surface, good growing conditions persist long after the first frost blackens the tomato or hosta leaves. Perennials, shrubs and trees transplanted in fall will focus all their grow-power on regenerating lost roots. When spring arrives, they'll have a much larger root system that's better able to sustain vigorous leaf production.
These roots grow much better as the soil cools into the 60oF range than they do in the 80 degrees heat of midsummer earth. The roots keep growing vigorously until the soil temperature drops into the low 40s, and some growth occurs whenever the soil remains unfrozen.
For a planter's purposes, then, fall is defined by when the soil begins to cool and plants stop growing new shoots and leaves. It's a time, too, when the rains return in many regions, and gardeners everywhere have more free time. In zone 7 and southward, the period for fall planting can be months long depending on the latitude. In cold areas, the fall planting window of opportunity is shorter. Gardeners there may have only a few weeks of optimal conditions. But there is virtually no place in the U.S. or southern Canada where gardeners can't successfully plant something in fall. Here's a rundown on the range of plants you can work with and appropriate techniques for easing your plants' transition to their new places in the garden.
Perennials
Many experts agree that fall is the best time to plant perennials. Allan Armitage, a professor of horticulture at the University of Georgia and author of the comprehensive new guide, Herbaceous Perennial Plants (Varsity Press, Inc., 1989), has grown perennials in Montreal, Michigan and now Georgia. He told me recently, "In the north, fall is just as good for planting perennials as spring. In Zone 7 and farther south, fall is absolutely the best time to plant them."
Spring- or early summer-blooming perennials, if planted in the fall, will put on a good display of blossoms the following spring. You can't beat that with a spring planting. Even autumn-flowering plants like chrysanthemums, helianthus or asters will thrive with fall planting, though you'll sacrifice that season's blossoming.
The best time for fall planting perennials, according to Armitage, is about a month before killing frost. That will provide two months or more of good root-growing conditions underground. But in Montreal, where frost comes in early October, he transplanted perennials in early September, getting good results with only a three-week growing period before frost.
Finding good-quality stock in local nurseries in autumn, however, can be a problem. Many of the plants will have been held in the nursery yard all summer and are often potbound. For that reason, Armitage says, the most dependable source of perennials for fall planting is from mail-order nurseries.
Perennials grown in containers, especially those that have become potbound, need a form of root pruning. Armitage pushes the fingers of both hands into the bottom of the root ball and gently tears the bottom half of it open a bit. On larger plants he may make a vertical gash through the bottom half of the root ball with a sharp spade. Then he spreads the split bottom open a bit, untangles bound roots and replants.
Until the ground freezes and root growth stops, make sure the plant gets the equivalent of an inch of rain a week. And mulch, says Armitage, is an absolute must. It saves water and helps keep the soil warm enough for root growth far later into the fall.
Established plants in your garden can be divided and replanted in autumn to increase your stock and rejuvenate the plants. When moving or dividing your own plants, Armitage recommends removing some of the foliage before digging to prevent wilting in the warm weather of late summer and early fall. On large-leaved plants that grow from basal rosettes, such as hostas, cut individual leaves in half Plants that send up stems are easier to deal with: just cut the stems back by about half When the leaves have been pruned, dig up as much of the root mass as you can with soil intact, transplant the plant to a hole to fit at its new site and water it in immediately.
Trees and shrubs For bare-root woody plants, including fruit trees, determining when to start planting and transplanting is a bit different than for perennials. Digging too early often stimulates new shoot and leaf growth, which in turn delays the development of winter hardiness. But once the plant begins to show the slightest change in leaf color, you're safe. That's the sign that the abscission layer between the stem and twigs has begun to form and that the top portions of plant have entered dormancy. Use the onset of leaf coloration in deciduous trees as a guide for moving evergreens, too.
For bare-root plants (that means most mail-order fruit trees, ornamental trees and shrubs), fall planting is only safe in areas that are zone 7 or warmer. And with some trees, you should wait until spring to plant. Oaks, for example, always seem to do better from a spring planting. And any species that is near its northern limit for cold hardiness is at risk in a fall planting.
"Root regrowth comes in two stages," says Davis Sydnor, a horticulture professor and researcher at Ohio State University in Columbus and a former nurseryman. "Elongation of intact terminals will occur any time of year the soil temperature is above 40 degrees F. When you transplant bare-root, you lose 95% of all the roots even when you do a good job. A containerized plant, properly root pruned, will lose about 50% of its root system. A bare-root oak will have essentially no intact terminals left, so it can't really do much but sit there through the fall and winter. Plants with more fibrous root systems will have a few intact terminals, so they can grow in fall."
Container-grown trees and shrubs can be planted safely just about any time, even in high summer or in winter until the ground freezes too hard to dig the hole. In summer you need to water frequently - even daily - until new roots migrate from the root ball into the native soil. In winter, the danger is frost heaving the root mass out of the ground, though mulching can prevent that. Fall-planted container stock will be well anchored by the time the ground freezes. And fall is ideal for container plants because it's the time for root growth, and moisture stress on plants is less than in summer.
Container-grown trees should always be root pruned. There are various ways to do this, says Sydnor. Use a sharp spade or an old kitchen knife to make three to five slashes (depending on container size) from top to bottom along the root ball. Then make an "X" three or four inches deep into the bottom. "Or cut the root ball with one slash about 2/3 of the way from the bottom toward the top, and splay the root mass out in the planting hole," Sydnor says. "Frank Gouin at the University of Maryland in College Park recommends this method. He calls it 'butterflying.' An advantage to his technique is that it gets more of the root fiber higher in the soil, where it will develop more root mass."
Digging In
Every step in the transplanting process should be directed toward encouraging a healthy root system. It starts with getting enough root mass when you dig up your own tree or purchase the plant. The root ball should be 11 or 12 inches wide for every inch of the trunk's diameter at the base of the plant, according to Sydnor. The hole the tree goes into should be at least six inches wider than the root ball. And since roots are reluctant to explore dense soil, it helps to rototill or fork the soil six to eight inches deep for several feet beyond that.
Sydnor cautions that the planting hole should actually be slightly shallower than is often recommended. 'As late as the 1970s, a lot of people were recommending that you put about six inches of fluffy stuff - peat, leaf mold, compost - under the plant. But that's disastrous. When you put a root ball with a normal soil density in there, or even a bare-root tree, it will be more dense than the stuff in the bottom of the planting hole. Eventually the root ball will settle through the less dense material and your tree will end up being planted too deeply. it could die, or just sit there not growing much, and you wouldn't know that something was drastically wrong," he notes. Sydnor advises planting the tree several inches higher than it grew in the nursery, even if this means leaving a few small roots exposed to air. Where the soil is very poor, or when planting containerized plants, Sydnor has a new technique for amending the soil.
"For nursery production we've come up with a highly oxygenated, moisture-retentive medium based on peat," he explains. "It has virtually no soil. It's great in the nursery, but when you plant that root mass in ordinary soil, the radical interface between the two media is a real barrier to root extension. Roots don't grow from a less dense medium into a more dense medium. it's almost as if the plant was still in the pot."
To create a transition zone for root growth, Sydnor recommends working peat or compost into the soil. Use enough to make up as much as one third of the soil volume extending a foot beyond the planting hole (and up to eight feet farther, if the soil is very poor and you want rapid tree establishment). Avoid homogenizing the organic matter with the native soil, though. instead, mix it irregularly, like a marbled cake, so that veins of organic matter extend into native soil. The richest concentration of organic matter should be near the root ball, with the veins thinning as they get farther from the tree.
"With bare-root transplanting, the extra organic matter is not as critical, but it's probably a good idea anyway. It creates a vein of moisture that the roots will follow. As the vein runs out, the roots come in contact with increasingly dense soil," Sydnor adds.
Stakes, mulch and water
When you set the tree and backfill, there is rarely a need to stake the tree. About the only time Sydnor thinks you should stake a tree (except for dwarf fruit trees, which have notoriously undersized root systems) is when there is a strong prevailing wind. Instead of using wires or straps that can damage the bark, Sydnor recommends using screw eyes. "In urban tree plantings they've found guy wires the leading cause of tree death. I would rather trade one to three 1/8- to 1/4-inch holes, a known wound of very small consequence, to a band of pressure all across the bark." Mulching the newly planted shrub or tree out to the drip line and beyond does wonders, says Sydnor. Keep the soil moist and free of competing grass and weeds out as far as eight feet, and the tree will respond with strong growth. Use about two inches of mulch (whatever is available and inexpensive). If you use grass clippings, however, don't put on more than an inch because they tend to mat and form a moistureproof barrier. And if you apply wood chips or some other mulch that is very low in nitrogen, first put on some fertilizer, at a rate of 3.2 ounces of actual N per 100 square feet.
Sydnor cautions against overwatering. The newly transplanted tree should get the equivalent of an inch of rain a week or two inches every two weeks. if you are unsure about when to water, he suggests planting an impatiens, coleus or ajuga in the hole with the tree. if the companion plant wilts and stays wilted after sundown, the tree needs more water. How do you know if all is going well? Gauge the tree's recovery by shoot growth the next season, says Sydnor. That can vary tremendously with the species. But, he says, "I like to see twig extension the first year no less than one fourth of average growth, For most species that average will be at least a foot a year. So twig growth should be below three inches for the first year after transplanting. The second year, the tree should be recovering well and put on six inches of growth per inch of trunk diameter. Take those measurements on the sunny side of the tree, from branches near the top."
When you see growth like that in the spring, you'll know you've done well for the underground portion of the tree. The roots may do their work out of sight, but the wise gardener doesn't forget them. Plant them well, then admire the tree from afar, letting the roots grow thick in the uncompacted, generously mulched soil that is the hallmark of the knowledgeable planter.
Copyright NGA
Reprinted with permission HouseNet, Inc.
Prime Time for Planting