In the Garden:
Pacific Northwest
September, 2008
Regional Report

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Short, warm days and crisp nights trigger leaf color changes, reminding me it's time to plant new trees and shrubs.

Fall: The Other Planting Season

As fall approaches and the need for watering, weeding, and fertilizing diminishes, most of us begin to think about putting the garden to bed and settling in for the winter. However, fall is not only a season for closure, it's a superb time for planting and transplanting. Many trees and shrubs establish themselves just as well when planted in fall as in spring, while some perennials actually do better. Hardy, spring-blooming bulbs must be planted in fall to develop a sturdy root system. And here in the Pacific Northwest, plants set in the ground in fall can continue growing right through a mild winter.

In the same way that the cooler temperatures of fall make working in the garden more pleasant than under the hot summer sun, the still-warm soil and cool air of autumn give plant roots a growth boost while slowing water loss from transpiration. In many areas fall brings abundant rains while still leaving the soil dry enough to be workable. All of this adds up to a lot of reasons why fall is a great season for planting.

Trees and Shrubs
The technique for planting in fall is not really any different than for planting in spring. To plant a tree or shrub, dig a hole a few inches wider than the soil ball or farthest-reaching roots. In compacted soil, make the planting hole at least twice as wide as the roots. Dig the hole with sloping sides rather than straight, to give the new feeder roots maximum room to grow, since most of them are in the top 12 inches of soil. Although it is often said that placing gravel or sand in the planting hole improves drainage, this is not true and I don't recommend it.

A plant's roots are naturally pruned when it is dug so the only root pruning to do at planting time is to clip off any broken or unhealthy ones. One exception is when the roots of container-grown trees are compacted or cracking the pot. In this case, use a sharp knife to cut through the encircling roots. Cut down the sides of the rootball in about four places and then slice an "X" on the bottom or the rootball, spreading the quarters apart before putting it into the planting hole. If you are planting a relatively mature container-grown tree with a large rootball, just splay the roots as best you can.

Unlike perennials, which are usually planted in beds, trees and shrubs are frequently planted alone. Since it's not possible to amend a very large section of ground around a tree, it's better not to amend the soil at all but to put back only the soil you removed from the hole. Amending only the planting hole causes the feeder roots to grow quickly until they reach the sides of the hole where the soil is poorer and more compacted. There the roots will stop and begin to circle along the sides, eventually girdling the tree. On the other hand, if you are planting a shrub border, you can amend the whole planting area with organic matter prior to planting.

The goal is for trees and shrubs to be set at the same soil level they were planted in the nursery pot. Plants will usually settle somewhat, so plant a bit high unless your soil is very sandy. If the soil is poorly drained, make a mound of soil at the bottom of the hole, and set the plant on it before replacing the backfill so that water drains away from the roots.

Aftercare
The easiest task to overlook in fall is watering, but new transplants must have adequate moisture to establish a good root system. Provide at least an inch of water a week to a newly planted tree or shrub right up to when the ground freezes or until rains take over for you.

Mulching is always a good idea, but especially so for newly planted trees and shrubs. Immediately after planting, spread coarse mulch such as shredded bark or wood chips 3 to 4 inches deep around shrubs, over an area two to three times the diameter of the rootball. Keep it a couple of inches away from trunks and stems.

Staking is usually unnecessary and can cause the tree to grow more slowly than if it were left unstaked. Research shows that a tree that sways somewhat in the wind will establish more anchor roots and add more trunk girth than one that is firmly staked. However, on an extremely windy site, staking may be necessary.

Don't stop thinking about the garden as soon as the weather begins to cool. Instead, use the wonderful autumn season to give your garden a new look by rearranging plants and adding new specimens purchased at those great end-of-season clearance prices. You'll get next year's garden off to an early start and give yourself the breathing room to enjoy its spring display.


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