Pruning New Zealand Christmas tree close to a swimming pool

Question from Suzanne:
How often should I prune it? how much can I cut it back?–probably 30 years old–probably at least 20 feet high. Neighbor has a swimming pool. I don’t want to take it out (it does grow to property line. Any suggestions?

Answer from Pat:
New Zealand Christmas tree (Metrosideros excelsa) is a virtuous tree and, if I were you, I would certainly not cut it down. Too bad the trunk is close to your property line and the neighbor’s swimming pool. You don’t mention the position of the swimming pool in respect to the tree or whether the tree shades the pool or if the problem is drippiness. I would not call this tree particularly messy except for the summer blossoms. If there is a problem with blossoms only, and if the swimming pool is south of the tree, wouldn’t a large umbrella or better yet, a Coolaroo Shade Sail or other brand, be positioned correctly to stop blossoms from falling into the pool? I have seen special structures built to protect pools or patios from falling tree blossoms and then the blossoms can be raked off or swept off with a long-handled tool especially designed for the purpose from time to time.

For correct pruning I would consult an arborist, but if that is too expensive then get the best company you can find locally to do the pruning and in any case, do NOT allow them to take off more than 20% of the foliage. The bark of New Zealand Christmas tree can be sunburned and over pruning can harm this tree severely, so don’t let it be over-pruned. If you opt for pruning, it’s okay to prune once a year. This is a tree that can be kept small and shrub-like if necessary, but once it is 30 years old and 20 feet high, it’s too late for that, but you could shorten the branches by tip pruning on the neighbor’s side.

If tip pruning of foliage (or hedging) does not do enough to stop the neighbor’s problem, then cutting the branches back in length is an option as long as you always cut back to a joint. After shortening a branch correctly, you should be able to walk away from it and no one should be able to tell it has been pruned because every branch that is left on the tree will still have a growing tip. There will now be a new tip with live foliage on the end. It will simply be shorter. (This type of pruning is the opposite of thinning a tree. When you thin out or “lace out” a tree, you cut out all the inside growth baring the branches. I don’t think this is what you want done here. Tell you pruners “No. We don’t want to lace out the tree. We want to drop- crotch it, and back-crotch the branches.”

“Drop-crotching” is an option on top for lowering the tree, and the same thing can be done with the sides of a tree. With drop-crotching, when the shape of the tree allows it, you cut the top off, down to the next joint. This is different from “topping” a tree. Do not allow “topping” (chopping the top off right through branches.) Topping harms trees. Drop crotching does not harm the tree, as long as you leave a new top to replace the old one you took off. What is harmful to a tree is cutting off branches by cutting straight through them leaving bare stubs with nothing to continue growing. (You often see this done to coral trees and eucalyptus and it is wrong.) This kind of pruning (when you don’t leave a growing tip on every branch) is extremely harmful to most trees.

Sometimes called “pollarding”, cutting straight through the top branches in fall is done on willow and sycamore in Europe. On sycamore and willow trees this causes a big knob to grow and then these knobs put out a proliferation of small whiplike branches in spring. The knobs grow bigger every year and sprout with new grow in spring that can be harvested every fall. Pollarding does not work for any trees other than willow and sycamore. Unfortunately untrained and uneducated pruners sometimes cut branches this way and that’s why it is so important to hire a good tree company with an arborist in charge or a foreman who knows what he is doing and won’t butcher your tree.

But with proper pruning by a good company you could cut back some this year which would produce bushiness further back, and then the following year you could cut back further. In this way you could prune it progressively and gradually, while lowering the tree and making it bushier without harming the tree. Also, a few offending branches could be removed altogether as long as you take them back to a joint and are not allowing the trunk or branches to be exposed to sunburn. Try to keep the tree somewhat balanced but without denuding it or leaving yourself totally exposed.