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Question from unknown (full conversation) -

When is the best time of year to plant trees?

Answer from Dr. Mike Kuhns, USU Extension Forester and Professor (sent 5/9/17) -

Trees are best planted when they are still dormant with tight, unopened buds in the early to mid-spring after the soil has thawed. Cool temperatures and good soil moisture in the spring help trees get established. Fall planting also works well for many species, though watering is critical if the fall is dry. Summer planting of B&B (balled-and-burlapped) and container plants can be successful, though hot temperatures, dry conditions, and non-dormant trees makes good care especially important and survival less sure. Bare root trees should only be planted in spring while still dormant.

Question - Of those types of trees, which is best?

Answer - Landscape trees and shrubs can be obtained in four basic types: balled and burlapped (B&B), container/potted, bare-root, and tree-spaded. Each type has advantages and disadvantages and none is ideal for all situations. Bare-root will give the tree the most naturally formed root system and they are less expensive, but they are not commonly available from nurseries. B&B trees are good because they have been grown for several years in soil and are more likely than potted trees to have a well-distributed root ball. Potted or containerized trees are the worst, with it much more likely that the tree will develop root system problems like girdling roots and buried root collars. Spaded trees are good but may not be available.

Question - How large does the root ball need to be?

Answer - With all four types you need to have an adequate root system – a good rule-of-thumb is that the root system, root ball, or container diameter or spread should be 10 inches to 12 inches for every inch of stem caliper (diameter at ground-line just above any basal swell). Therefore, a 3-inch caliper tree should have a 30 inch to 36 inch wide root ball as a minimum. Root ball depth is not as critical as width but should be larger for larger trees.