Pruning (part 1)

For some, pruning is really an art while for most of us is just one way of getting the most of our plants. However, before stepping into the tricks and secrets of how to best prune your plants it is important to know how plants grow.

How do they branch? When are they most active? Do all plants respond equally to pruning? These are some of the questions which one must have in mind before pruning a plant or even before deciding to have a specific species or variety of plant. Plants can have very different forms and shapes, and in some cases these can even vary between individuals of the same species depending on the conditions under which they grow. However from the gigantic Mountain Ash (Eucalyptus regnans) to the smallest weed on the ground one can find patterns and similarities in the way the plant body distributes its aerial parts above ground.

We are all familiar with the pyramidal shape of many pine trees and spruces for example, in which there is a big round trunk tapered towards the apex with many lateral branches, longer and thicker at the base and shorter and narrower closer to the apex. The older and higher the tree gets the thicker the base of trunk and lower branches become while the apex is surrounded by shorter and younger branches, e.g. Norway spruce (Picea abies). This type of branching and grow pattern is called monopodial is common to many trees and smaller plants, e.g. orchids. Typically, when you see one stem with leaves and flowers only, it is mostly indicative of a species with monopodial growth. In monopodial growth, there is what is called apical dominance where the main stem with its apex at the tip is the main, most active and dominant growing part of the plant. The lateral branches and their apices are dormant, with their growth inhibited, or they grow more slowly compared with the main stem.

On the other hand, many fruit tress like peaches, oranges and other ornamental trees like elms, yews, etc, have many branches which gives very diverse shapes and forms far from having a main or dominant branch. In these cases, the apical meristems, i.e. the tissues where cells multiply and grow, i.e. the tips, produce flowers and eventually fruits and they will wither at the end of the growing season. The growth in this part of the plant is stopped and the plant will no longer grow from here. Next season, the grow starts in its immediate adjacent meristems below and their tips will also wither at end of the respective growing season.

This is why, the plant branches in all directions without having a clear dominant direction. This grow pattern is called sympodial growth and is usually used by pruners to give plants funny shapes as many sympodial species respond well to pruning by branching and growing more laterally or diffusively, e.g. maple, camellia. Typically, this is the case with many climbing species and other ornamental species like roses.

However, being a sympodial species does not necessarily mean that it will respond well, or the way we wanted, to cutting and pruning. A good example is the lilac, Syringa sp. While being a typical sympodial species lilac responds very slowly to pruning and cutting. Usually, it takes two to three years to flower again after pruning. This, of course, depends on how extensive and damaging the pruning was. On the other hand, many monopodial species are slower in responding to pruning and one must be careful on deciding which parts to cut. Furthermore sometimes, the single stem is the only stem the plant will ever have, like in many orchids.

Special thank you to Dr Pablo Cabrita (Phd. Plant Physiology)

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