Plants will Grow Up

While I don’t think most hobby and leisure gardeners require an absolute understanding of technical horticulture terms, I do think that 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 plants to grow upright and what controls it. Geotropisam and hormones within the stem tip buds are in charge of stem extension and a phenomenon in the tip-top bud of the plant contains yet another controlling factor called “Apical Dominance”. Since this hormonal feature is found in the top of a plant, and usually the tallest and most centered tip, which is the critical growth area in most cases, managing apical dominance is as simple as leaving in place or taking the top bud or stem 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 off the top stem growth bud and the flower. As a matter of fact, this is a good habit with most 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 it less likely to wilt when freshly 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 most importantly, by removing the tip, you have removed the agent controlling apical dominance, and in its absence the existing side buds are free to develop into new stems, allowing for or causing 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 with all the more blooms instead of just one stalk of color.

In addition to providing more blooms per plant initially, contuned pruning will keep the plant shorter and bushier and this pruning or pinching will also remove seed heads 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.

While apical dominance is very technical technical, it is really a fairly simple concept 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 In the long run, that leads to a more beautiful garden, more satisfaction, and more peace of mind yet this summer.