Nursery Tree Selection Guide

This winter has been an odd one so far climatically-speaking. I know I've taken advantage of the good weather this past weekend to take some hikes, and I saw a ton of people doing just the same thing. With warmer than normal weather for this time of the year, many people have spent time in their yards the past few days as well, and have started to think about what they'll want to install this year.

As the backbone of your garden, trees play an important role in the look, functioning, and biodiversity of the landscape. Adding trees to an outdoor space can improve soil health, help to prevent erosion, increase privacy, and add color and interest. Between the months of December and March is a great time to plant trees in the Bay Area, especially fruit trees. I've gotten many questions in the past from customers, clients, and friends and family concerning the specifics of selecting a nursery tree out of the many rows of specimens that seem to all look the same. In response, I've put together a short go-to guide for all of you that will fill you in on what you need to know. 

In choosing a specific tree for your landscape, there are a few important things to consider. The first is shopping at a nursery or other plant source that is compliant with federal and state laws and regulations. Our state, to protect both our economy and natural biodiversity, has enacted laws that affect the transport and sale of plants. To ensure that you are purchasing a tree that will be safe to plant in your garden, make sure you are purchasing from a reputable seller.
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A second factor to consider when purchasing a nursery tree is going native. Native trees are those that are endemic to the Bay Area, and therefore have evolved to survive in our unique climate. These trees also tend to be more drought-tolerant, and will generally perform better and be more resilient than imported species. To do a search of native trees that will do well in your area, head over to the California Native Plant Society's Calscape website:

Calscape Native Tree Search

Once you've selected your nursery and species of tree, you can head down to your chosen seller and check out their inventory of trees for sale. As you settle on which specific tree or trees you'll bring home, pay close attention to the following:

Proper Identification
Ensure that the tree you are considering is labeled properly. Most nurseries have wonderful labeling systems and will put stickers on individual plants, others are not so thorough and some work may need to be done to locate a tree that is properly labeled. Be sure that you are buying the tree that you came to purchase. Also, when looking at the label, ensure that the size of the pot is listed, and that it is correct. There's no reason to pay the price for a 20-gallon tree when you're only getting a 5-gallon, just because of an incorrect label.

General Tree Health Markers
There are many markers to look for in a nursery tree that will increase the chances it will adapt well to your garden and live out a long, healthy life. Inspect nursery candidates for the following:

Tree should be relatively free of pests.

Crown should not be damaged by wind, pruning, pests, or other factors.

Leaves should look typical for the time of year and growth stage of the tree.

Shoot growth should be typical for the age and size of the species of tree.

Trunk should be fairly straight, vertical and free of damage, sunburn, cracks and bleeding, and signs of insects or girdling.

Tree height and diameter should be typical for the species and container size.

Root system should be free from biotic and abiotic issues, and root distribution should be relatively uniform.

Crown Characteristics
​The crown of the tree should have a central leader, either the original one or a replacement that has established after a heading cut has been made. If the original leader has been headed, a new leader at least 1/2 the diameter of the original leader needs to be present. Check out the three photographs below for a visual representation of what you should be looking for.

A single, central leader is preferable.

Headed trees that have retained a leader are acceptable.

Codominant stems or heading without leader retention is unacceptable.

Main Branch Characteristics
Main branches, also called scaffolds, should be distributed radially around the main trunk and vertically along the trunk, forming a somewhat symmetrical shape that is typical for the species. The following aspects of the main branching qualities of nursery trees should be examined:

Main branches should be well-spaced.

Branch diameter should be no more than 2/3 the diameter of the trunk measured an inch above the branch.

Attachment of scaffold branches should be free of included bark.

Temporary branches should be present along the lower trunk (especially for younger trees less than 1.5 inches in trunk diameter). No temporary branches should exceed 3/8 inch in diameter. At this diameter, they should be pruned off.

Trunk Characteristics
The diameter and taper of the trunk should be sufficient so that the tree will remain vertical without the support of a nursery stake (eventually). The trunk should also be free of wounds and other damage caused by insects or disease.

The trunk diameter (measured about six inches above the soil surface) should be within the diameter range shown for each container size:

Container Size
#5
#15
24-inch Box

Trunk Diameter in Inches
0.5" to 0.75"
0.75" to 1.5"
​1.5" to 2.5"

Root Characteristics
Main root system shall be free of circling or kinked roots. It may be necessary to carefully dig into the soil a bit to inspect the root system.​​ Check out the photographs below to see a reference for preferable and unacceptable root composition. The tree should also be rooted well into the potting medium it is in, and should not be pulled out of the soil mix easily.

The upper-most roots of the collar should be present within an inch of the soil surface (they can be above or below the soil surface). Also, when the root ball is removed from the nursery pot, it should be free of large circling and bottom-matted roots. In other words, the tree's root ball should not be trying to burst out of the pot that it is in. 

The last thing to check on your chosen tree is the current moisture status of the soil. Nursery trees should be receiving water on a regular basis; their roots cannot move past the confines of their pot to find water, and if they are water-stressed, they could undergo a more dramatic shock period after they are installed in your garden, and may not make it. After you've completed this last check of your tree, you're ready to check out. Keep in mind that many nurseries will offer delivery services (either for free or for a charge) for larger trees or orders with a large number of plants. Make sure to get all of your delivery information squared away before leaving the nursery if you choose to go this route. 

Choosing a nursery tree is neither a quick nor an easy process, but being picky about your selection will ensure the health of your purchased tree and increase the chances that it will survive in its new home. For more information on planting your new tree, visit the Year in the Garden module of Kristi's Garden Club. 

Until next time, 
Kristi.
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Resources & References
Guideline Specifications for Nursery Tree Quality
Choosing the Right Tree at a Tree Nursery