Fall is the Best Time to Plant Trees

Planting Trees in Fall

Allen Robinson: Ask a Master Gardener

Sunday, September 30, 2018

Q: Is it true that fall is a good time to plant new trees? If so, what do I need to do to be successful? Alex R., Tulsa

A: Fall is clearly the best time to plant most container-grown deciduous trees and those with balled and burlapped (B&B) root balls. This is because, in the fall, the trees have huge energy stores that are used for growing new roots rather than producing leaves and fruit. This will allow the tree to enter the following growing season much better able to handle the summer stresses. Also, although the air temperatures are dropping, the ground temperatures are still warm enough to encourage good root development for some time. The exception to this rule is that evergreen trees and bare-rooted plants should be planted in early spring.

Of all of the newly planted trees that die in the first few years, the problem is almost always due to faulty planting techniques and inadequate aftercare. So let’s discuss this.

First, it is best to dig a wide but shallow, saucer-shaped hole two to three times the diameter of the tree’s root ball and no deeper than the root ball itself. If you simply dig a hole the size of the root ball, particularly in clay soil, it will be similar to planting it in a clay pot and the tree will be either too dry or too wet much of the time. If you are planting in shallow clay soils, the hole should be shallow enough to elevate the crown of the root ball 2-3 inches above grade to help with overall root system drainage.

When planting trees, it is recommended that you use only native soil for backfill. Studies have shown that trees do better if no amendments are added back to the native soil, as it may delay establishment and promote disease. If you decide to fertilize, apply a slow-release type only to the top of the soil after planting.

Eliminating grass from the tree’s base significantly improves growth rate and health. After planting, apply 2-4 inches of loose mulch in a 4- to 6-foot circle around the base of the tree and keep it well-mulched for the first three years. This circle will keep unwanted grass away from the dripline and commercial weed eaters away from the tree trunk.

All newly planted trees need supplemental watering for the first three years until a mature root system develops. They need at least 1 inch of water per week and more if extremely hot and windy conditions exist. Wilting of the trees’ leaves may indicate a need for more water, but be aware that too much water can also produce wilting. If in doubt, simply feel the sub-soil.

If the tree is on a slope or in a windy area, stake it only until the tree feels firm in the ground, which could take up to one year. After the first growing season, remove all stakes. If not removed, the stakes will adversely affect the tree’s structural integrity and delay tree growth.

For more detailed information on this subject, see OSU Fact Sheet L-440 (Tree Planting Guide).

Garden tips

• You can continue to replant or establish cool-season lawns like fescue until mid-month. The mowing height for fescue should be lowered to approximately 2½ inches for fall and winter cutting.

• Plant cool-season annuals like pansies, ornamental cabbage or kale, snapdragons and dusty miller when temperatures begin to cool. Begin planting spring-flowering bulbs like tulips, hyacinths, crocus and daffodils.

• There is still time to plant radishes and mustard in the fall garden. Use a cold frame device to plant spinach, lettuce and various other cool-season crops for production most of the winter.

• Take tropical water garden plants indoors when water temperatures near 50 degrees. Stop feeding fish at this temperature. Close the water garden for the winter by placing hardy plants in the deeper areas of the pool and cover it with bird netting to catch dropping leaves during the winter months.