Featured Expert
Jeffery Johnson
Plant Coordinator
Minnesota Landscape Arboretum
Chanhassen, MN

Q: I have a newly planted tree in my yard. What should I do for pruning it?

A: Well, it's a common question that we run into as far as long term care of plants. Pruning is one of those aspects of care that really needs a little bit of attention over a long period of time. Frequent attention is much better than giving a whole bunch all at one time. The other issue is timing of pruning. Here we are in late June at the Minnesota Landscape Arboretum, and we're coming into another window of opportunity for pruning. Regarding timing, the issue is - I like to use the analogy of an airplane, and an airplane has takeoffs and landings, not unlike what the cycle of a plant goes through. The most dangerous time for an airplane is during that takeoff and landing period. When the airplane is on the ground, similar to the plant being in dormancy, you can do a lot of things to it. The other thing is when the airplane is up and flying, you can shut the engine off for a little bit of time, and restart the engine and come back for a nice safe landing. The same thing goes with tree pruning. The takeoff - the spring flush of growth, and the landing - when the plants are going into dormancy into the fall, are two times when we really should avoid pruning. But otherwise, as far as disease and insect considerations, during the midsummer and during the dormant season are really some fine times to do some pruning on your landscape plants. This dwarf crabapple is just one plant that we would typically have people doing some pruning on in their yard, and what we want to do is think about again, going back to the right plant in the right place, is the long term health of the plant, and the long term size and form and texture of the plant with regard to what we're going to take out. So thinking about what the plant is going to look like long-term is very important in deciding how we're going to approach the pruning. Very basically, we want to do thinning cuts whenever possible. Thinning cuts, meaning that we're going to take out a portion of the plant, and this portion is going back up into the plant, causing problems for the long term. So, I'm going to take out a branch that's going back into the plant. And you can see the effect there is to open up the plant without distorting the shape or form of the plant. What I really like to strive for is that we don't want to deform the plant through pruning, but we want to make it look better than it did originally. We're thinking about the long term health and maintaining the overall natural character and habit of the plant through thinning cuts, which is very important. The other issue in making a proper pruning cut is the branch collar, or if you're dealing with smaller branches, making the smallest wound possible without leaving a stub is a rule of thumb that I like to follow. We want that plant to be able to seal the wound over as fast as possible to reduce the chance of any kind of infection from decay organisms or whatnot.

The other issue is the question of whether or not to use pruning paint. Pruning paint really should only be used in a couple of very narrow circumstances where we're dealing with a particular insect or disease phenomenon. One of the issues is oak wilt, and we have a lot of oak wilt in Minnesota, particularly in the northern areas of the Twin Cities, but there are some oaks out in the western portion of Minnesota, and April, May, and June are the high infection periods for oak wilt. If you have storm damage or something that you have to prune out in April, May, or June, then go ahead and use pruning paint. But otherwise, pruning paint can actually do more harm than good, particularly on something like this crabapple here, or a maple tree, or any of the other trees or shrubs in your landscape where the pruning paint can prevent the plant from sealing that wound over. We want that wood to dry out in the inner portion and then the cambium layer forms what's called "wound wood" around the wound and closes that wound eventually. Pruning paint can actually deter that process or inhibit that process. So, pruning paint is only recommended in some very narrow circumstances.

images: pruning | after pruning | dwarf crabapple

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Last updated: Tuesday, February 01, 2005