Plants Will Grow Up

While I don’t think most leisure gardeners have to lose sleep over acquiring strong understanding of plant physiology and technical horticultural terms, I do think it is helpful to understand some of the principles determining a plant’s growth. Two of the most basic of these factors are what causes plant to grow upright and what controls it. Hormones within the stem tip buds are in charge of upright growth and a phenomenon in the tip-top bud of the plant contains yet another controlling factor called “Apical Dominance.” Since this feature is found in the top of a plant, which is the critical growth area in most cases, managing apical dominance is as simple as taking the top or tip buds off a plant. In essence, when we prune, we are blocking the plant’s natural tendency to grow primarily upward perhaps into a tall, gangly plant or at least a less than full and beautiful one.

The benefits of breaking apical dominance can be easily seen in a simple garden petunia. I recommend that before planting your petunias, you snip the top stem growth bud off (which may contain a flower bud.) As a matter of fact, this is a good habit with annuals. I know it can be heart stopping to eliminate that first spark of garden color with pruning shears or your thumb nail, but the many benefits far outweigh the short-term loss. First, by trimming the top bud, you slow the upright growth of the plant and remove some of the most succulent tissue, which makes the plant less likely to wilt when transplanted. Second, pinching to remove some of the top helps to balance the tender plant against any root loss that may occur during the transplant. Finally, and perhaps most importantly, by removing the tip you have removed the agent controlling apical dominance, and in its absence, side buds are free to develop into new stems, allowing for a shorter, bushier plant with more blossoms.

The benefits of breaking apical dominance are evident even in plants that are supposed to be tall and thin. For instance, I trim my snapdragons to about three inches above ground so that the plant yields three to five upright stems, instead of just one, with all the more blooms. In addition to providing more future blooms per plant, continued pruning will keep the plant shorter and bushier and will also remove seedheads and allow the plant to bloom well into autumn. You can also simply pinch to maintain uniformity and remove any stems that are growing in an awkward, unsightly direction.

Breaking apical dominance can be used to direct the growth of larger plants and trees, also. By understanding that any plant will ultimately grow upward, you can use directional pruning, and/or espalier, to keep a plant’s growth against a wall, away from a power line, along a fence rail or anywhere else you might choose. Just cut slightly above the bud that is growing in the direction that you want the stem or branch to go.

While the chemistry of apical dominance is very technical, it is really a fairly simple concept to follow that allows you and me to plan our plants’ growth and shape them from the outset rather than randomly chopping at what will become unsightly branches and stems. And, in the long run, that leads to a more beautiful garden, more satisfaction, and more peace of mind.