Fall is the best time of year to plant most trees and shrubs. Usually temperatures are cool, but not too cold for root growth, and rainfall is plentiful: the perfect conditions for new roots to form and plants to become established. In addition, many garden centers get in a fresh batch of plants, so you might find that particular tree or shrub that was sold out when you looked for it in the spring.
It is important to give roots a good place to spread out, so when you plant, dig your hole wide but not too deep. Wide is usually defined as 2 or 3 times the size of the container your plant came in. Just as important, don't dig the hole too deep. You want the plant to rest in the hole slightly above the level that it was growing in the container. If you over-estimate how deep the hole should be and have to back fill, remember that the loosened soil underneath the plant will settle, lowering the plant in the hole. You may want to compensate for the settling by planting a bit higher. The depth of the hole is important because Memphis soil generally contains a lot of clay, and clay soil equals poor drainage.
After you've dug your hole there is a big temptation (at least, this is true for me) to add soil conditioner, compost, or other amendments to encourage those roots to reach out into the soil and help the plant off to a good start. Plant scientists have learned that this is the opposite of what actually happens. Adding organic matter creates a difference in the texture of the soil in the hole and the surrounding native soil. This difference causes problems with water movement, as well as encourages roots to grow in a circular pattern in the amended soil rather than spreading out into the native soil. Just think about what roots do when they bump against an obstacle like the edge of a flower pot (or hard clay soil) : they take the path of least resistance and just circle around in that soft, amended soil you provided. So you want to create a more hospitable environment by loosening the native soil in a wide area, but resist the urge to add amendments.
Also, it is a good idea to check the root ball after you remove the plant from the container. If the plant has been growing in the container for a while, the roots may be crowded together in the pot. In this case, you may want to tease the roots apart with your hands to encourage them to spread out in the planting hole. If the plant has been in the container for a long time, the roots may be pressed together in a thick mass. In this case, you'll need to be ruthless about spreading the roots. You may even need to use a knife to score through the root ball. Cutting circling roots encourages the plants to send out new roots, and these new roots will have a better chance of growing into the native soil.
Roots that grow in a circular pattern around the plant, sometimes referred to as "girdling roots" can, over the course of years, actually strangle and kill an otherwise healthy plant. Sometimes this condition results from improper planting, and sometimes we inherit the problem from the garden center where we bought our plant. Case in point, consider the picture below. I came across this small tree last week, one in a group of newly-planted trees. My guess is that they were planted this past spring, as most of the trees still had the nursery tag on them. Notice the root encircling the trunk. This will prove to be disastrous over time.
What to do about this condition? At a minimum, the encircling root should be clipped so that it can't continue to encircle the tree. But this root makes wonder what condition the rest of the root ball is in. Since this is a small tree and appears to be planted fairly recently, I would dig it up and inspect the root ball. I'm guessing other problems may exist and could be corrected now. If no corrections are needed, little or no damage will be done by digging it up and replanting it, as long as it is well-watered through the fall.
Speaking of watering, this fall's strange, hot and dry weather conditions mean that you need to be extra vigilant about watering. Newly planted trees and shrubs have a small root system so they need regular, frequent waterings. This fall, mother nature has not been helping us out much with watering.
Click here for a short University of Tennessee Extension fact sheet on planting.