"Fall is for planting" is a point-of-purchase advertisement seen at nurseries, garden centers and other retail outlets during late summer and early fall. While the primary motivation for the ads likely is to increase sales and profits, the message is good advice from the standpoint sound horticultural practices. This especially is true for trees and shrubs.
There are a number of advantages associated with fall planting, one of which is convenience. In fall, there often is more time to do a good job of what can be a somewhat labor-intensive task. There are fewer demands for pruning and weed control and other landscape maintenance chores than in spring or summer. Additionally, when the soil is still warm and the air becomes cooler in the fall, there is less stress on plants while the roots grow and become established.
In fall, many deciduous trees and shrubs are approaching dormancy or already may have dropped most of their leaves. This means they will not be losing large amounts of moisture as is the case in spring when new leaves and top growth develops rapidly, often at the expense of root growth. The absence of this stress allows for energy to go into the production of new feeder roots that prepare the plant for next year's spring growth. A tree or shrub that is healthy and vigorous at the time it is planted in the fall will have adequate nutrients stored in its woody twigs and branches to support good root growth, even though leaves are not present for the manufacture of food.
The most ideal time for fall planting somewhat depends on where one lives. At our latitude, trees and shrubs should be planted from September until the end of October to allow adequate time for good root development before the soil cools. This does not mean that trees or shrubs cannot be planted later. However, since root growth is correlated with soil temperature, little is any root growth may occur until the soil warms the following spring.
If a plant is marketed as a "balled and burlapped" specimen that was dug from soil similar to the composition of the soil into which it will be planted, little or no improvement is needed to the "back-fill" soil used around the root ball in the planting process. The same is true for container-grown specimen planted into relatively good garden soil. For heavier soils, the addition of organic matter can help to speed root establishment. A ratio of one part of organic matter to two parts of existing soil (by volume) is ideal. If the roots are growing in almost total organic matter (as in the case of some container-grown stock), remove some of the growing medium from the upper and central area of the root ball. This allows heavier back-fill soil to settle closer to the base of the trunk, next to the root system.
Planting depth is of great importance when establishing trees and shrubs. A general rule is to never plant trees or shrubs deeper than they were growing. Wide, but not deep, holes for planting are best. Wide holes (two to three times root ball diameter) provide more room for amended back-fill soil; shallow holes reduce the tendency for plants to settle. Balled and burlapped nursery stock should have the upper ring of wire supporting the soil ball removed and twine used to hold the burlap to the tree trunk loosened.
Watering a tree after planting is just as important in the fall as after spring planting. Make sure the root ball is well watered as the back-fill soil is added to the hole. Since the back-fill soil is looser, it wets more quickly than the dense soil of the root ball. If dry weather follows planting, make sure the root ball is kept moist during the fall, but do not over water. There is not a rapid moisture uptake by plants in the fall, but water still is needed.
When plants are purchased in the fall, they should be planted promptly. Prompt planting not only allows for more time for fall root establishment, but it also prevents drying damage to the plant's root system. Any root damage from drying delays rapid root establishment which is the primary reason for fall planting.
Whether or not to stake a newly planted tree depends on both the plant and location. The objective of staking is to prevent the root ball from shifting and shearing off newly formed feeder roots. Plants with a large, massive root ball often have adequate weight to sit firmly in the soil and avoid shifting. Plants will small, light-weight root masses (e.g. container-grown plants) may need support. Deciduous trees and shrubs tend to resist winter winds better than evergreens. Pine trees or similar plants are more apt to be shifted by winter winds and benefit from adequate support, at least for the first year. Staking or other forms of support are of greatest benefit in areas subject to periods of heavy rains accompanied by strong winds.
If trees are staked after planting, the support should not be so restrictive as to prevent the trunk from moving slightly. Wires or other staking materials tend to injure sensitive young trunks if kept too taut. A general rule is to stake a tree only as high as necessary to keep the root ball steady but still allow the upper trunk to move in the wind. Light, corrective pruning also can be done at the time of staking. Additionally, if sun scald is of concern, wrap the trunk of the tree with a light-colored material.
The above narrative applies to trees and shrubs that are very hardy. Species marginally hardy at our latitude are better saved for spring planting, since there is the chance of cold injury if the winter that follows is very severe. If such plants must be fall planted, the planting should be done as early as possible to allow for maximum root growth. Anti-transpirants (a.k.a. anti-desiccants) can help protect marginally hard plants such as broad-leaved evergreens during their first winter following planting.
The wisdom imparted by an ancient Chinese proverb is a good closing point. It reads, "The best time to plant a tree was 20 years ago. The second-best time is now."
REVISED: September 4, 2020