Selecting the Right Cover Size
Measure the width or diameter of the tree canopy in feet from one side to the other. Measure the height of the canopy.
Choose a cover size that is at least as big as the larger of the two measurements.
For young trees the width and height measurements may be about the same. For older well-managed trees, the width of the canopy will typically be greater than the height. Choosing a cover just larger than the diameter of the tree will be a good match.
For an unpruned, less-managed tree the height measurement may be greater, even much greater, than the width measurement. In such a case you will probably want to shorten the height of the canopy by pruning. If you prune the tree to be shorter, you can easily harvest fruit on the highest limbs while safely standing on your tallest ladder.
For faster growing trees such as some apples and pears, choose a cover that is big enough to allow 2-4 ft of vertical growth during the season. Apple and pear trees typically grow the fastest in the vertical direction during the summer. If you have a tree that is 12 feet in diameter, but is only 8 feet of vertical canopy, there will be a few feet of vertical room for the tree to grow vertically during the summer in a 12 foot cover.
See the page on Pruning for more information.