The phrase "fall is for planting" is seen frequently at this time of the year in retail outlets that market plant material, especially nursery stock and hardy perennials. Skeptics, no doubt, consider this to be a sales tactic by the store to decrease inventory before the onset of winter. The phrase, however, has merit and is based on sound horticulture principles. Even though trees and shrubs can be planted throughout the growing season, fall-planted material is not subject to hot and dry weather which requires more careful maintenance until the plant is established.
There are a number of benefits associated with fall planting. For example, in fall, there often is more time to go a good job. There are fewer demands for pruning, weed control and other landscape maintenance chores associated with spring and summer. Additionally, abundant spring rains often leave the soil to wet to work for some time. Autumn normally features drier weather.
Another benefit from fall planting is the reduction of transplant shock. The latter refers to stresses occurring in recently transplanted trees and shrubs. When the soil still is warm and air temperatures cool, there is less stress on plants while their roots grow and become established. In fall, many trees and shrubs are approaching dormancy or already have dropped most of their leaves. At this time, they will not be losing large amounts of moisture compared with spring, when new leaves and top growth develop rapidly at the expense of root growth. The absence of this stress in fall allows more energy to go into the production of new feeder roots that prepare the plant for next spring's growth. A plant which was healthy and vigorous at the time it was dug and planted will have adequate nutrients stored in its woody twigs and branches to support fall root growth even though leaves are not present to manufacture food.
The best time for planting may depend on where you live. Generally, in our hardiness zone, trees and shrubs need to be planted from September until the end of October to allow enough time for good root development before the soil becomes too cold. This is not to say that trees may not be planted later. However, later planting will produce little if any new root growth until the following spring, negating a major advantage of fall planting.
If a tree or shrub has been dug from a nursey field which has soil similar to the soil into which it is to be planted, the backfill used around the root ball probably needs little, if any, improvement. When the soil is heavier, the addition of organic matter can loosen it and help speed root establishment. If the plant has been grown in a very organic soil, mix organic materials (e.g., peat moss or compost) into the backfill at a rate of about 1/3 organic matter to 2/3 existing soil, by volume.
Container-grown nursery stock often is produced in growing media that is almost totally organic matter. If this is the case, remove some of the growing medium from the upper and central area of the root ball. This allows heavier backfill soil to settle closer to the base of the trunk of the plant and next to its root system. Never set plants deeper than they were growing in the field or nursery container. Wide, but not deep, holes are preferred for planting. The latter tends to reduce the tendency for excessive settling.
Watering a plant thoroughly after fall planting is just as important as after spring planting. Make sure the root ball is well watered, as well as the backfill soil placed into the hole around the ball. Since the outer soil is looser, it wets more quickly than the soil of a dense root ball. If dry weather follows planting, make sure the root ball is kept moist during the fall, but do not overwater. There is not a rapid moisture uptake by plants in the fall of the year, but water still is needed.
When purchasing plants for fall planting, plant them promptly. Prompt planting not only gives more time for fall root development, but it also prevents drying damage to the plant's root system until it eventually is planted. Any root damage from drying delays rapid root establishment which, as previously mentioned, is the primary benefit derived from fall planting.
Cool season grass species such as bluegrass and fescue make rapid root growth in the fall. Therefore, it is important to mulch a newly planted tree or shrub planting to restrict the growth of turf roots into the loosened backfill soil. Mulch also tends to act as insulation, causing the soil to remain warmer in late autumn. When applied, mulch should be no deeper than 2 to 4 inches but should be as wide as is acceptable to the tree owner. Taper the mulch so that it is less than 1 inch deep next the trunk.
Whether or not staking is required after planting often depends on both the plant in question as well as its new location. Plants with a large, massive root ball frequently have adequate weight to sit firmly in the soil and avoid shifting. Plants with small, light-weight root masses often need some sort of support. Plants that drop their leaves are less subject to being shifted by winter winds when compared with evergreens. Pines, or other similar species, tend to be affected by winter winds and benefit from staking, especially during the first winter. Staking or other forms of support have the greatest benefit in areas subject to heavy rains accompanied by high winds. When staking, never wrap brace wire directly around the trunk. Use something like a short length of garden hose to protect the trunk from damage by the wire. Also, it is best to allow a little "wiggle room" for the plant's trunk, rather than staking in such a way that the plant cannot move.
Very hardy trees and shrubs respond well to fall planting. Marginally-hardy species often are better saved for spring planting, since there is a chance of cold injury if the winter that follows is especially severe. If such species must be fall planted, do so as early as possible to allow the greatest amount of time for good root growth. Materials called anti-desiccants can help to protect broad-leaved evergreen species (e.g., holly or rhododendron) from leaf scorch injury their first winter after planting.
For additional information on tree planting, please consult MU Extension publication G6850 titled "How to Plant a Tree" (https://extension.missouri.edu/publications/g6850).
REVISED: September 16, 2021