Here’s a little tree trivia: Do trees grow up or out?
Another way to phrase the question is: If your tree has a branch three feet off the ground, how high off the ground will it be in 10 years?
The answers are essential when it comes to growing healthy trees.
Trees grow out. And in 10 years, that branch will still be three feet off the ground.
The words up and out are just a matter of semantics. Trees only grow at the tips of the branches, which contains meristem tissue and where cell division takes place. A tree’s height comes from this continued growth of the upper branches, not because the trunk pushes up from the ground. Make sense?
Now you might be asking why this tree trivia is important. Many of us have young trees in our yards. These trees are a long-term investment providing shade and increased property values. Knowing how they grow prepares us for how we should prune them.
Lower limbs can become a hazard as the tree grows. These limbs can cause us to hit our head while mowing or make us duck when walking along the sidewalk. The process of raising the tree canopy, called limbing up, removes these low-hanging hazards.
Many of the branches on a young tree should be considered temporary. At some point you can remove any limb below five or six feet to provide head clearance. But it is important not to get too aggressive when raising the tree canopy.
Lower limbs are full of leaves necessary for making energy and increasing the growth rate. If the lower limbs are cut off too soon, there will be fewer leaves, which means less energy and slower growth. Only remove a few limbs at a time as necessary.
Keep this image in mind: About one-third of the tree should be trunk and the remaining two-thirds should be the crown — the part with leaves and branches. This ratio provides enough leaf surface for good growth while still allowing for the removal of low hanging limbs.
Another guide for knowing when to raise the canopy is to look at the diameter of the branch. The smaller the diameter, the quicker the tree seals the wound, which reduces the potential for rot and decay. Remove lower limbs before they reach three to four inches in diameter.
One of the keys to proper pruning is to make the cut at the time of year when the plant can seal the wound as rapidly as possible. Unfortunately, fall is not that time, as the plant is going into dormancy and not focused on producing new tissue. Late winter and early spring are the periods of most rapid growth for plants and the best time to prune.
Feel free to now impress your friends with your knowledge and, of course, put it to good use to insure a healthy, happy tree.
Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Got a question for him or other university extension experts? Email them to firstname.lastname@example.org.