An Art of Constraint: Part 2

In part one, we introduced the idea of constraints, and how they apply to bonsai. Let’s dive deeper into the types of constraints we typically use for bonsai training. There are three primary constraints that we apply as bonsai artists: the size of the pot (including the frequency and severity of repotting), how much and how often we prune, and the application of wire.

The next section will probably seems obvious to anyone who has been doing bonsai for a while, but bear with me. There’s a point to all this. How and why we choose to apply certain constraints at certain times is what makes this an interesting conversation, and is where we’re ultimately going with this. But let’s start with the constraints themselves.

Constraint #1: The Pot
Bonsai is about trees in pots, so by definition we are constraining the tree within the pot itself. This is one of the main things that keeps the tree small. Less room for roots == less room for growth. And occasionally, when the pot fills up with roots and becomes root bound, we re-pot, we trim the roots, and we freshen the soil.

A collection of fairly standard mass-produced bonsai pots

Decisions, decisions …
When we re-pot, we have a choice of how much we want to constrain, and that choice comes in the form of choosing the next pot size. Are we scaling up? Scaling down? Holding steady?

We also choose how much root work to do. We can choose to just “slip pot” into a larger container, we can do a light re-pot where we do some minor clean up on the roots but otherwise leave most of the root ball intact, or we can do extensive root work. This choice will impact how the tree grows for the current season, as well as in future years.

A light re-pot into a slightly larger pot on a portulacaria afra (mini jade)

By the way, most bonsai trees I see have been put in bonsai pots way to early. If your bonsai looks like a stick in a pot, and it’s in a bonsai pot, it will remain a stick in a pot for a very, very long time. I don’t get many things already in bonsai pots, but when I do, often my first step is to get it into a larger pot where it can stretch out.

Also, keeping a tree in a tiny pot can weaken it over time. Sometimes the best possible thing you can do for your tree is to sacrifice short term development, slip-pot the tree into a larger container, and nurse it back to health. Restrictive bonsai techniques should be applied to strong, healthy plants only. Rule #1 of bonsai: Don’t kill your tree.

Constraint #2: Pruning
Another way to constrain the tree is pruning. Pruning a tree by definition scales it down, at least a little. Pruning a tree also slows things down, and locks in the progress you’ve made on the branch so far. Branches need to extend in order to thicken, so pruning temporarily suspends that thickening process.

Boxwood nursery stock after a fairly significant pruning.

Pruning also encourages the tree to produce new growth that’s closer to the trunk, which can improve the sense of scale for the tree. Pruning to constrain the growth of the tree is the primary tool for reducing the scale of a tree over time and making it look like what we expect to see in a bonsai.

But nobody is forcing you to pick up the shears. At any given time, you can choose whether to prune or to wait. That is no small responsibility. I can spot an over-pruned bonsai a mile away. There is occasional value in pruning heavily, but when it’s done too often the health of the tree is often sacrificed, and the tree doesn’t get a chance to stretch out and grow like a natural tree would.

When working on early stage material especially, you need to let the tree itself do a lot of the work, and that work comes in the form of growth. Slowing that down prematurely slows down the process. It’s fine to do that if you have a reason, but be sure that you do in fact have a reason.

Constraint #3: Wiring
A third constraint that we use to shape our trees is wire. Wire is used to force a branch into a particular shape, and it is held there until such time as you remove it. I think of this as a constraint because you are forcing a branch to conform to a particular shape and location.

Wiring some initial motion into a larch.

Over time, as the tree grows and adds wood to the branch, the new bend is locked in, and the movement holds permanently. Wait too long, however, and the wire will bite into the branch and the branch will become damaged. A little bite is OK, but you can easily ruin a branch by leaving the wire on for too long. Ever see a tree grow into a chain link fence? It basically does that to your wire. It’s really cool that it can do that, but not usually helpful from an artistic point of view.

Guy wires being used to hold branches in place on a boxwood.

Constraints in Nature
In nature, trees have their own constraints. Amount of available water, the amount of uncontested space they can find to grow their roots, the length of the growing season, etc. Nature is not a friendly place, and trees have done a remarkable job at adapting to her cruelties.

If you cut a tree down and look at it’s rings, you can tell if a tree had a year of abundance or a year of scarcity. It’s reflected in the thickness of that year’s ring. Likewise, heavy snowfall can bend or break branches, branches die back and rot off, etc, etc. Nature leaves it’s mark on the trees over time.

Important note: there are a lot of misconceptions about bonsai out there, and one is that we constrain our trees by withholding water and fertilizer. That one is generally not true, and can be quite dangerous for the tree if you attempt to impart character in that way.

Now, sometimes nature can be a bitch, and you’ll have an extra hot day where your tree suffers, or you’ll accidentally leave your tree exposed to a colder temperature than it typically can handle, or you’ll get a huge batch of aphids or other pest that damages the tree, or some other such mishap.

Sometimes these things are happy accidents, and leave an interesting and indelible mark on your tree that adds character. Other times it kills or severely damages the tree and can ruin years of effort. So, unless you really know what you’re doing, it’s best to just water and fertilize your trees as perfectly as you know how, and accept nature’s happy accidents along the way rather than try to create them on purpose.

For the purposeful character building, let’s primarily focus on pots, pruning and wire.

Stay tuned for part three, where we discuss creative application of constraints when developing bonsai.