Spring is a time of an awakening plant world full of blooms and endless possibilities for the coming growing season.  It’s a time that many of us think about updating our landscaping, making it the most popular time of year to plant trees and shrubs. 

When you combine the mild temperatures and bountiful rainfall of spring it creates a wonderful planting opportunity.  However, at the time of spring planting, we often fail to think about the harsh, summer conditions ahead for our new tree.  No matter how early we plant or how favorable spring weather may be, all newly planted trees are in transplant shock for several years following planting and drought stress during the first summer is often a critical factor in their long term survival. 

Urban Tree Survival Rates

Past research has shown high mortality rates and short lifespans for street trees planted in the city right-of-way, or boulevard, by homeowners or municipalities themselves. A few highly cited research papers from the late 1980’s and early 1990’s report shockingly low average lifespans of urban street trees at only 7-13 years.  More recent papers have identified somewhat longer average lifespans but the statistics remain grim compared to the potential lifespan for many trees. 

Street trees are certainly subjected to harshest urban conditions, representing the “worst case scenario”.  Research looking at trees planted in home landscapes and parks suggests a much higher survival rate and much longer expected life.  However, most of this research points toward the immediate 5 years after planting as the most critical period in an urban tree’s life, reinforcing the vital role of proper planting and follow-up care.

Overcoming Transplant Shock

All newly planted trees are in state of shock until they become “established” at their new planting site.  This transplant shock has been shown to persist for 2-3 years in most trees and it is generally true to assume that the larger the tree, the longer the transplant shock, sometimes extending it up to 5 years.

What is the major hurdle that a tree must clear to overcome transplant shock and become “established”? Most of the answer lies in root development and many of the unseen things that occur underground.  Since a balled and burlapped or containerized tree has a small amount of roots compared to above-ground plant parts, the crux of tree establishment lies in the development of an adequate root system to support the plant. 

Although trees don’t have high soil nutrient demands, like a tomato plant, the texture and structure of soil are quite important to ensure adequate air and water exchange for root development. If you feel like the soil in your planting hole has poor composition, consider adding amended soil.  Also, dig your planting hole shallow and very wide, as wide as you deem practical.  The loosened backfill in your planting hole provides a wonderful space for root development compared to the relatively compacted soil outside the area you dug.

Determining Planting Depth

Proper planting depth has also been identified as a major factor in tree survival.  Ensure that your tree is planted at the proper depth by identifying the root collar before digging a hole. The root collar (of root flare) is the area at the base of a tree trunk where the trunk tapers outward as it transitions to root tissue.  Many times the root collar is not at surface level of a pot or root ball, making it necessary to dig down in search of this structure.  Set the depth of your planting hole based on the location of the tree’s root collar, it may be much shallower than you would think.

Post Planting Care

After backfilling the hole around your tree, be sure to add 2-4 inches of mulch on the soil surface to help retain soil moisture in the hotter part of summer.  As we get into late June and July, be prepared to provide water for your tree any time we have not received 1-2 inches of rainfall in a given week.  It is preferred to water for long periods once a week as opposed to short duration, many times a week, since this mimics our natural rainfall. 

Plan to mulch and water your tree carefully next year, and possibly the following year for larger trees, to be sure it becomes established in its new home and doesn’t just become “one of the numbers” as so many urban trees do each year.

More Information

For more detailed information on tree planting and after care, visit the International Society of Arboriculture’s website, available by clicking here.  It features a “Tree Owner Information” webpage with great information on all aspects of tree care.