Pinch to Grow an Inch

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That’s a familiar saying with absolutely nothing to do with bonsai. Or might it? It certainly recalls to mind Dennis Vojtilla’s rule of thumb. At least my thumb, which works for my larger trees, and is as you guessed, one inch wide. And right now, I am sure that whether we are growing conifers or deciduous trees, we are all in the middle of pinching season. With that in mind, I wanted to remind you about some ground rules on pinching and what we are trying to accomplish with the technique.  

When it comes to spring growth on our trees, we have several choices on how to handle it. The first is maybe not obvious, and probably the least understood. That is, do nothing. Let your tree grow. You might want to do this if you are propagating stock via seeds, cuttings, etc… Or you might be trying to increase the tree, or more specifically, trunk mass. Or we might be growing a single flush, long-needle pine (Ponderosa, White Pine) and if we pinch or prune, we can cause excessive needle elongation. Maybe you are just trying to get a tree healthier and stronger. Whatever the reason, doing nothing at this time of year really is a valid technique. The other things we can do are pinching and pruning.  

When I think of pinching, the very first tree that comes to mind is a Japanese maple and by the time you read this, we are pretty much past the first flush of growth. The idea behind pinching is to remove the central shoot and by doing so we control the strength of the shoot and prevent it from elongating. Pinching controls the inter-node length. It mostly stops elongating once you pinch it. If you miss that window, then you have to fall back on pruning techniques, and if has gotten too long, you have to prune off all that you gained so that you can regrow a piece of ramification to the desired length. And if you are like I was last year and miss that window over and over, pruning again and again, the result is a knob that then has to be pruned off even farther back.  

But all of this assumes one thing. That you pretty much have the “size” and shape of the tree that you want. If you start pinching before the tree is ninety percent there in terms of trunk and major branch structure and size, you are just not going to get there. Pinching slows down development to a crawl, which is exactly what we want for a tree in refinement.  

I got a lot of “feedback” at the last meeting about the lack of pinching in the Deshojo Maple that I displayed. I had to explain to several folks that I was purposefully trying to elongate one side of the canopy, as well as the overall size of the tree. Later, I will work on those branches with pruning. However, I will say that those shoots were longer after the meeting than before. Things were moving quite fast indeed, and those shoots were nipped the very next morning. By the way, with my one-inch thumb, I like to use a small pair of scissors when “pinching”. I can see what I am doing much better and I don’t damage the tender leaves.  

But that brings up the next, very important point. If your tree is not styled, either by wiring or pruning, or whatever, you won’t know what to pinch, or prune for that matter. If the tree is not styled you won’t know if that branch needs to be longer or shorter. Furthermore, the tree really can’t take advantage of your pinching and pruning work.  

I was recently asked if wiring inhibited back budding and my reply was that it was necessary for back budding. When a tree has its branches styled appropriately, each branch will receive the maximum amount of light, or energy from the sun. Styling exposes more branch surface to the sun at an angle of incidence to maximize all those precious rays. It’s really hard to convince the tree that it needs more branches when it is not getting light there to support them.  So how does a tree react to pinching? We’ve taken the strength out of the stronger parts and redirected it to the weaker parts. That’s why we need to pinch over a broad period of time. Shoots can emerge a week or two after the general pinching, or even a month, and we have to keep on top of those. But those shoots were activated or accelerated by the previous week’s pinching exercise. We use pinching to move strength from strong to weak buds.  

However, pinching does not generate new buds. It only strengthens or activates buds that are already there. Need more buds, go back to strategy one. Style it and let it grow, grow, grow. Once it gets strong, it WILL back bud. Then you can think about pinching. This strategy also works well in other species, including conifers like spruce, firs, and short needles pines. It is very effective at balancing strength. I am in the middle of conifer pinching right now. I must use pinching on something like a Doug Fir that is extremely apically dominant. If I don’t, those top shoots hog all of the resources the tree has to offer. My job is to keep that from happening, and redistribute energy. Sort of the socialism of the tree world.  

Heading into May and June we enter the pruning time of year. After the leaves have hardened off, which you can tell by their darkening color, firm attachment to the tree, and general thickening, it’s time to prune. By the way, when we say leaves, we mean broad leaves, needles, and any other foliage types. This is where species are more similar than different. And once again, we are back to just what are our objectives? By not pruning, even if we pinched earlier, we leave the tree with some strength. Again, this is a very valid strategy for building a tree. But if we have new branches that have hardened off and are strong enough, we can prune back to these, always.  

On a deciduous tree, we can usually prune back to any set of leaves and get a second flush of growth. But do not count the first set of “pre-leaves” on a shoot. They may not develop a bud and make sure to leave at least a pair leaves or shoots at any location, or you do not gain any ramification, and you will likely lose too much strength. This is also another way to reallocate strength to another part of the tree. At times, I allow the tree to grow unchecked until May, accumulating energy, and then make my major pruning cuts so that the tree has plenty of strength and time to respond during the summer season.  

You can extend this all the way to the severe “trunk” chop. Just make sure in any case that you provide ample protection from the sun which can now burn leaves, branches or especially trunks if their protective canopy of foliage is removed. For some reason, it took me more than one experience to figure this out and I would like to save you the heartache.  

There are many species specific techniques and timing to pruning and we can’t really go over all of those here. The point of this article is that if you are actively developing trees, whether they are in refinement or developmental stages, you can use pinching and pruning to effect rapid development of your trees. Stay happy, water well, and fertilize!

Scott Elser