Planting Trees and Shrubs in the Fall

September Is for Shoveling

by Michelle Sutton and photographs by Larry Decker, August 26, 2011

I had the niftiest graduate research project. The public works crew and I planted 150 trees around the city of Ithaca, New York. We planted half of them in spring, half in fall. We chose three tree species (an oak, hackberry, and American hophornbeam) that have historically been described as “hard to transplant” or “fall transplant hazards.”

Measurements over many subsequent years showed that the ones dug from the field nursery and planted—i.e., transplanted—in fall did just as well as the ones transplanted in spring, defying nursery lore about the perils of fall transplanting—at least for these three species. For a wide range of species, my adviser had observed anecdotally in her decades of planting trees in Ithaca that fall transplanting was just fine.

Fall is a grand time to plant most trees and shrubs, so long as you properly prepare your planting site and give the plants proper aftercare. Good preparation means making sure the site is well amended with organic matter and the planting hole is as wide as possible so the roots have some opportunity to explore the larger soilscape. Good aftercare means watering deeply one to three times weekly, depending on how dry it is, until the ground freezes and giving the plant a wide, mulched bed so its roots don’t have to compete with turf grass.

Fall planting’s virtues are many. The air is cooler, so there’s less water loss through the leaves. This is much less stressful for a newly transplanted or planted tree or shrub than being planted, say, in late spring just before a heat wave hits in June. Fall planted trees and shrubs still need deep watering to encourage root growth in their new situation, however.

Another advantage of fall planting is that while the air is cool, the soil is still warm, which enhances root growth. Root growth has been found to occur as long as soil temperatures remain above 40 to 45 degrees Fahrenheit—and keep in mind that soils cool much more slowly than the ambient air, so this soil warmth lasts well into fall. Late August and September are great times to plant, but in many cases, you can go into early October, and if you find a specimen on sale in November and you’re willing to assume a little risk, plant that plant.

What makes late fall planting riskier? It depends on what kind of winter weather comes. When it comes to plants and winter damage, as woody plants professors like to say, “It’s not how cold it gets, it’s how it gets cold.” Do very cold temps come on suddenly and without benefit of snow on the ground, which serves as a kind of protective mulch over tree roots? Or does the cold come gradually and give the plant a chance to “harden off”? How it gets cold is more pertinent.