Most gardeners get the urge to plant ornamental trees and shrubs during the warm weather of spring and summer. However, the cooler temperatures of fall are the preferred planting conditions for woody plants. Fall weather conditions are preferable to spring and summer because water shortages in the hot summer season negatively affect the establishment of the plant’s root system.
Also in the fall, the demands of tree branches and leaves lessen as they go into dormancy. Soil temperatures don’t decrease as fast as air temperatures, and tree and shrub roots can continue to grow past dormancy. When temperatures increase the following spring, fall-planted ornamentals should have a well-developed root system ready to soak up water and nutrients.
One of the most common errors for gardeners is improper planting technique, in particular planting too deeply. It may seem insignificant, but many trees and shrubs have not survived because they were planted just two to three inches too deep. For example, tree roots are designed to grow in the top several inches of soil. The upper layer of soil contains the correct amounts of oxygen needed for proper root growth. Planting too deeply disrupts oxygen levels and may also cause fungal rot on the base of the tree trunk. Always dig planting holes at the same height as the root ball or container soil. To be on the safe side, planting 1/2-inch high may help correct for soil settling.
Another common mistake is the size of the planting hole. Most people will dig a hole just large enough for the root ball of the tree or shrub to slide in. For best results, planting holes need to be at least three times the size of the root ball. This is extremely important for heavy clay soils like that in most of Columbia County. Digging out the extra soil around the root ball will allow air pores to be added to the soil as it is replaced in the hole. When new roots begin to grow, they will easily expand through the freshly dug soil ensuring a solid start for the new plant. With only a small hole dug, new roots may struggle to expand through the tough native soils. This can lead to root girdling and early plant death.
Many gardeners want to know about adding soil amendments, such as premium planting mixes, during planting of woody ornamentals. There is still debate over whether or not adding soil amendments to planting holes of woody ornamentals is beneficial or not. Most of the research indicates there is not a great benefit to amending the soil, especially for trees. Tree root systems will quickly expand several feet in every direction and will not gain much benefit from soil conditioners near the trunk. In fact, it may actually cause roots to not expand as far because there isn’t as much need to seek out water and nutrients.
Fertilizers should be added to new tree and shrub plantings only if recommended by a soil test. Slow-release fertilizers are best used on woody ornamentals. They can be spread over the top of the root zone or incorporated into the expanded planting hole during transplant. Another recommended addition is a two- to four- inch layer of mulch added after planting to aid in moisture retention and to discourage weed competition. Mulch should be pulled back a few inches from the tree trunk to prevent fungal disease issues.