Be a Better Gardener: Tree Planting, Now Is the Time

By Thomas Christopher

One aspect of gardening on which there is nearly universal agreement is tree planting. On a personal level, most of us value the shade, flowers and fruit that reward such an act. Environmentalists favor tree planting as a way to combat climate change. Urban planners and activists know that more trees translate into a significantly cooler, more pleasant cityscape.

How many of us know, however, that early to mid-fall, not spring, actually is the most favorable season for tree planting? That’s the message I got recently from Pete Smith, the urban forestry program manager at the Arbor Day Foundation. Educated as a forester and an arborist, Pete is now based at the Arbor Day Foundation headquarters in Lincoln, Neb., where he helps the Foundation distribute and plant 10 million trees a year.

Fall is the best time to plant a tree partly due to the physiology of trees. Trees respond well to the cooler, typically moister weather of fall, sending out new roots vigorously when transplanted then. Even as the weather cools, the soil will retain some warmth for quite a while, especially if insulated with a blanket of mulch, so that root growth typically continues after above-ground growth pauses. A fall planting gives the new tree many more weeks to grow roots than a spring planting before summer arrives, bringing with it the stress of high temperatures, and, frequently, drought. This is a particular advantage in southern regions, where a number of states have moved their Arbor Day celebrations to the fall, but it applies also in the north, especially during this era of a warming climate.

Another benefit of fall tree planting is that nurseries and garden centers are typically less overwhelmed with customers then. You’ll find that sales personnel have more time to give you their attention in fall, and the trees themselves are less in demand and more available. At the same time, most nurseries and garden centers are commonly anxious to sell off remaining stock in the fall, and you may find bargains.

In the Northeast, fall planting season for trees runs from the beginning of September to the end of October, according to Pete. Conifers should be planted early in this interval; deciduous trees tolerate a later planting. Whatever kind of tree you select, Pete recommends buying container grown trees for fall planting, and to stick with modest sized specimens, such as those in five to 10 gallon containers. These smaller trees are easier to handle, require a smaller planting hole, and typically settle into their new home faster than larger specimens, so that in a few years the smaller tree will overtake in its growth the one that was larger initially. 

Get the tree into the ground, Pete advises, as soon as you can after bringing it home. Don’t enrich the soil in the planting hole — that discourages the tree’s roots from venturing outs into the surrounding soil and, anyway, most native soils are perfectly adequate for tree growth as long as you have selected a species suited to your region (the nursery personnel can advise you on that). Make sure to set the root collar of the tree, the flare in the trunk where the major roots join it, even with the soil surface. Planting trees too deeply is one of the major causes of failure in transplanting.

Water the tree during rainless intervals after planting, giving it an inch of water a week. Stop watering when the ground freezes, but start again when the growth resumes in the spring and continue through the rest of that growing season – during rainless weather, for over-watering can be as harmful as under-watering. Don’t rely on a lawn irrigation system, Pete adds. It will not moisten the soil to a sufficient depth.

Mulching around the tree out to the area under the tips of its branches will help to protect it against drought and, by eliminating weed growth, reduce competition with the tree’s roots. Pete likes arborist’s wood chips as a mulch, applied 3 to 4 inches deep but not piled up against the base of the tree. Finer-textured mulches, such as the ever-popular ground bark, will compact sufficiently that they actually shed water. 

Follow this handful of rules, Pete says, and your tree planting will most likely meet with success. It’s not a difficult process — especially if you save it for the fall.

Be-a-Better-Gardener is a community service of Berkshire Botanical Garden, located in Stockbridge, Mass. Its mission, to provide knowledge of gardening and the environment through a diverse range of classes and programs, informs and inspires thousands of students and visitors each year. Thomas Christopher is a volunteer at Berkshire Botanical Garden and is the author or co-author of more than a dozen books, including Nature into Art and The Gardens of Wave Hill (Timber Press, 2019). He is the 2021 Garden Club of America's National Medalist for Literature, a distinction reserved to recognize those who have left a profound and lasting impact on issues that are most important to the GCA. Christopher’s companion broadcast to this column, Growing Greener, streams on WESUFM.org, Pacifica Radio and NPR and is available at berkshirebotanical.org/growinggreener.