How do you plant a new tree? Most people know to dig a hole “twice as wide and deep as the root ball” (according to the label I found hanging from the branches), then stick in the tree, making sure the roots are well buried. Amend the backfill with plenty of compost, pile it over the roots and tamp it down firmly. Finally, securely stake the thin trunk so it won’t wiggle in the wind. Right?
This advice was being questioned as far back as 1980, but it is still widely practiced, much to the detriment of the poor plants.
Let’s take each step and see what current advice is according to the experts (like those digging up dead trees at Colorado State University, finding out why they died, and figuring out what needs to be done differently so they thrive instead).
We’ve hauled our tree (or shrub) home from the garden center. What do we do first? Dig a hole. Whether you’re planting a small shrub or a large tree, the advice is the same. Dig the hole twice as wide (three times is better) but no deeper than the roots. The roots will want to grow sideways; making the hole wide and shallow encourages them to spread in the right direction. Loosening the soil beneath the plant eventually causes it to sink, leading to a myriad of problems and an early demise.
But, surely we want to make sure those roots are far underground—isn’t that where they grow? Actually, no. Most roots are in the top foot or two of soil, where the air and water are. Yes, roots need equal amounts of air and water, and burying them too deeply will cause them to suffocate. Sometimes, in a desperate bid for survival, the tree will produce new roots higher on the trunk, but these are rarely sufficient to support a long life. The growth of these secondary roots merely delays the inevitable.
The right way to situate a tree is to ensure that the root flare—where the trunk widens into the roots—is above ground and the root ball is one to two inches above grade. You may have to remove excess soil if the tree was planted too deeply in its container. (When transplanting shrubs, keep the soil at the same level as it was in the container.)
How about amendments? If your soil is really poor, amendments help, but remember that the roots of a mature plant will extend far beyond the amended area—or at least they should. Roots are finicky; they often refuse to cross a boundary from one type of soil to another. If you need to add amendments, try to gradually decrease the amount as you approach the edges, creating a continuous gradient from amended to native soil. This is especially important when the soil in the container is quite different from that in your yard. You want those roots to venture outward.
If, when you tip the plant out of its pot, you notice that the roots are going in circles, feel free to loosen and untangle them. Unless you have a tiny, fragile seedling, it’s fine to do some rearranging.
Should you tamp the soil down? Yes, but don’t compact it too much. Remember that need for air and water. Just firm it with your hands. No stomping!
Finally, what about staking? The current advice is to avoid stakes if possible. Bending and flexing causes the trunk to thicken and strengthen and the roots to lengthen. However, if the tree is particularly top heavy, in a very windy area, or being planted where it could be jostled (such as near a playground), then stakes may provide some insurance.
The purpose of staking is to stabilize the roots while allowing the top to move. Therefore, don’t stake up high (as this landscaper did, left)—keep the ties low, as with the tree on the right:
Research has shown that trunks will get sturdier above the place where the ties are. Trees that were incorrectly staked will develop a skinny bottom, with a thicker trunk higher up. Not only will it look odd, but it will snap off in the first strong wind or heavy snow.
There are two more things you can do to help your new tree survive. One, wrapping the trunk may protect it from both deer and sunscald. This is particularly important in winter, and something to keep in mind for next fall.
Two, mulch to keep the soil moist, temperatures more even, and weeds under control. Don’t pile the mulch around the trunk—that encourages rot and gnawing rodents—but do apply a three to four inch layer over the backfill area. Too much mulch directly over the root ball can reduce the amount of oxygen reaching the roots.
Plants aren’t cheap, and we want to give them the best start possible. This is one area where doing things the same old way isn’t the best option.
For more information on planting a balled & burlap tree, see my previous post: Planting Done Right.