USDA plant hardiness zones are based on which climate measurement?
- Average annual rainfall and snowfall
- Average annual maximum summer temperature
- Average length of the frost-free season
- Average annual extreme minimum temperature
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D. Average annual extreme minimum temperature
The USDA hardiness zone map is drawn from the average coldest winter temperature each year, so it predicts cold survival only. It says nothing about summer heat, rainfall or soil.
Reference: USDA Plant Hardiness Zone Map; arborist study guide: Tree Selection
Which tree is the best choice for planting directly beneath overhead distribution lines?
- A species that matures at about 20 feet tall
- A columnar species maturing at 50 feet
- A tall species planted and pruned yearly
- A fast-growing species that can be topped
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A. A species that matures at about 20 feet tall
A small-maturing species stays clear of the conductors for its whole life. Planting a tall tree and relying on repeated pruning or topping creates ongoing cost, poor structure and an electrical hazard.
Reference: Arborist certification study guide: Tree Selection (site considerations)
How deep should a tree be planted?
- So the trunk flare is at or just above grade
- So the top of the root ball is 4 inches below grade
- So the lowest branch is level with the finished grade
- So the graft union is buried at least 2 inches deep
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A. So the trunk flare is at or just above grade
The trunk (root) flare should be visible at or just above the soil surface, with the ball resting on undisturbed soil. Planting too deep is a leading cause of decline and girdling roots.
Reference: Arborist certification study guide: Installation and Establishment (planting depth)