I recently received this question from Wendy in Wisconsin,
I have a 15 yr. old sargent crab apple, multi-trunked, planted 6 ft. from the house, under a large window 8 ft. from the ground.
The hope was the tree wouldn’t grow beyond 8 ft. in height, but it’s now more like 10 ft.…Last year, because the tree had grown above the bottom of the window, I pruned the ends of all the top branches (i.e. shortened the tree)… This year there is vigorous new growth (3-4 ft., with multiple branches from a single cut) from all the cuts I made last year…
I’ve actually thought about removing the tree and replacing it with another young Sargent or a Sargent Tina and widening the borders of the bed to give the tree more room.
Do you have any other suggestions?
Did you know that pruning can actually cause a tree to grow more? Yep. Cutting branches off a tree can cause the tree to grow more in the future.
Some days it sure seems nothing is as simple as it should be in life!
Yes, you can actually cause your tree to get bigger through pruning it.
The reason is that the buds at the end of branches release hormones that limit how much other buds in the tree are allowed to grow. When those buds are removed through pruning, the other buds can grow like crazy.
So basically, whenever you are pruning a tree you are affecting its’ hormonal balance. Since they don’t make Midol or chocolate for trees, we will look at how the types of pruning cuts you make impacts tree regrowth.
Types of Pruning cuts
There are three types of pruning cuts that can be made. They impact how the trees respond in terms of suckers, water sprouts and shoot regrowth. The three types of cuts made are:
Heading cuts – Shortens the branch shoot, but makes the cut between lateral branches that grow off the shoot, or to a lateral that is less than 1/3 the diameter of the parent.
Thinning cuts – Removes the entire branch back to its point of origin.
Reduction cuts – Shortens the parent to a lateral that is at least 1/3 the thickness of the “parent” branch.
How different pruning cuts affect how the tree regrows
Heading back branches and especially the leader results in vigorous growth from buds just below the cut. The further back the branch is cut, the more numerous the number of shoots will usually be. If you just cut back some of this year’s growth, you usually won’t get a lot of regrowth. If you cut way back into previous year’s growth, then you are more likely to have problems with suckers, water sprouts, and huge growing shoots.
The regrowth after thinning cuts and reduction cuts are more widely dispersed throughout the tree. Individual shoots that grow are less vigorous than those from similar heading cuts.
Tip #1 – Only make reduction and thinning cuts
Crabapples are notorious for creating suckers, water sprouts, and just plain real long growth shoots after heavy pruning.
They are doing this for a few reasons.
Root to Leaf Balance
One reason is that they are trying to rebalance the amount of leaves that they have for their amount of roots. Tree’s roots and leaves are always in balance. When there are too many leaves and not enough roots, the leaves experience stress from not having enough water. The tree stops leaf and branch growth and directs its energy to growing its’ roots until the tree’s system is back in balance.
Likewise, when you prune a branch the tree loses leaves. It then grows a lot in order to regain the leaf to root balance.
So What Does This Mean For Pruning?
It is best to limit the amount of pruning you do. This will keep the tree’s leafs in balance with its roots. If you remove half of a tree’s branches, get ready for a furious regrowth especially on crabapples. You are best to limit your pruning to 25% of the tree’s branches. This will reduce the amount of suckers, water sprouts and real long shoots you get after the pruning.
Tip #2 – Shorten long sprouts & remove water sprouts and suckers completely
A good way to remove suckers and water sprouts is to snap them off from the trunk or branch they are growing off of right when they start growing in spring before they get woody and hard.
If you leave them you will get something similar to this:
Tip #3- Prune in early to mid-summer
The best time to prune a crabapple and not stimulate a ton of growth is in the summer after they are done with their large flush of spring growth. They just spent a lot of energy producing new branches and leaves and will not have enough reserves to grow back immediately.
Since crabapples form flower buds for next year in mid-summer, you ideally will want to do this before that time. If you don’t mind sacrificing a few flowers next year, mid-summer is also fine.
Tip #4 – Forget fertilizing
It is also important that no fertilizer is applied the year of or after heavy pruning. Nitrogen should not be applied because the root system under the tree is large enough to provide water, oxygen, and stored food reserves to all of the above ground portions of the tree before any cutting was done.
Crabapples are one of the most tolerant trees of heavy pruning. Crabapples are after all, really just an ornamental form of an apple tree. Apple trees in orchards are pruned in ways that would make your Sargent crab shake in fear like a plaque of Japanese beetles was coming. There is no reason to replace your tree if you are willing to spend the time pruning it a few times a year.
If you found this article helpful or have any other pruning related questions you would like me to cover in a future post, please comment below.