Why fall, not spring, is THE time to plant that new tree.

September 14, 2022 · 3 minute read
Why fall, not spring, is THE time to plant that new tree.

It has been a pretty rough summer, with nearly intolerable heat that seemed like it would never end. But with cooler morning temperatures and less humidity, it feels like fall is right around the corner.  While fall usually has people thinking of pumpkin spice everything and fall festivals, arborists and horticulturalists start thinking about tree planting.  If you haven’t seen the banners outside of your local nursery, or the bumper sticker on your landscaper’s trucks, then I will let you in on a little secret: fall is for planting!

After a long, cold winter, most people crawl out from under their blanket cocoons in March, eager to fill their yards and landscape beds with beautiful, new plants to welcome warm weather and beautify their properties.  It is easy to understand why this is a natural reaction, as spring is a time for rebirth and new life – so why wouldn’t it be the best time to put new plants in the ground?

It all comes down to roots. Without a healthy and well-established root system, a plant cannot support itself structurally, or search for water when the heat of summer starts pumping.  Plants installed in the spring need months of time to acclimate to their new home and LOTS of water to ensure that roots do not dry out and die back.  Constant watering creates a lot of work, which can easily be forgotten as summer activities pull you from your diligent watering schedule.  Good news though – fall weather is perfect for root growth, and, most of the time, Mother Nature will take care of most of the watering for you!

Roots of woody plants, trees, and shrubs grow best when soil temperatures range between 65 to 75 degrees Fahrenheit. These are common soil temperatures in the spring and fall, but the main difference is what comes after those seasons.  Fall planting allows for good root growth with cooler soil temperatures and (usually) adequate rain to reduce the amount of supplemental watering needed.  While root growth does decline and stop as winter sets in, the plants go into dormancy and stop all growth, which greatly limits their water needs over the colder winter months.  When spring finally arrives, the plants come out of dormancy and have yet another season of favorable weather to grow stronger roots before the heat begins to stress the plants.

With fall being the best time to install new plants, the next step is to make sure that you plant the trees correctly.  There are many guides online regarding proper hole sizing, backfill material, and depth, which can give you good guidelines.  Nearly all of these recommend digging a whole twice the diameter of the root ball and backfilling with original soil from the hole.  While this is great in a perfect world, I will be honest that I have never once planted a tree to the specifications provided in these guidelines, as I am simply too lazy to dig such a big hole.  More important than hole size is the dynamics of the hole where the tree is being planted.

When using an auger or even a shovel to dig a hole, the sides of the hole can become very smooth and glazed. This creates a transition that tree roots do not want to grow through, so the tree will grow roots to the edge of the hole and begin circling in the planting hole.  This greatly limits root expansion, and is very similar to planting the tree in a pot in the ground.  The easiest way to avoid this issue is to use a shovel to break up any smooth or glazed walls of the planting hole, which allow the roots to spread into the existing soil beyond the planting hole.  Secondly, it is not recommended to amend this soil in any manner with compost or fertilizer mixed into the soil. This again creates a rooting environment where roots only want to stay in the amended and aerated soil of the original planting hole, and will not venture out.  Finally, never dig the hole deeper than the root mass of the tree, as settling soil over time will make the tree sink, and the root flare can become buried over time.

After the hot, dry summer we have been through, we have been seeing a significant number of trees succumb to the stresses of the season.  It is important to help regenerate our urban forest with new trees and shrubs.  Utilize the coming weather this fall to give your new trees and shrubs a leg-up by installing in the fall rather than spring.