(u)Keeping(/u) Them Looking Good .......
About a week ago I was asked to write something about what drives a plant's reaction to pruning, and how we can use the plant's predictable response to pruning to help us keep our plants attractive and establish control over their growth habit. I'm not really sure where to start, so I'm going to muse a little about 'goals', hopefully to help establish some (of your) priorities, with the confidence that there will be a 'lead-in' to the pruning discussion as that topic winds down.
How many of us actually work toward an established goal when it comes to our plant's appearance? Probably only a few. Most of us water when we think the plant needs it, fertilize using the same method, give our plants the best light we can, and maybe pot up now & then. We want our plants to grow fast, stay nice and green, and look attractive at all times.
Growing fast doesn't necessarily equate to good health, and surprisingly .... neither does a plant's being vividly green. In both cases, we can manipulate nutrition to the plant's disadvantage in order to achieve faster growth or greener color, so when the advice to add Epsom salts or ferrous sulfate (Ironite) to plants to 'green them up' comes along, remember that the advice is usually coming from someone who really doesn't understand nutrition .... or they would be suggesting an approach with less potential to be limiting; or would understand that the odds of there being actual magnesium or iron deficiencies based on a scarcity of the elements in the soil are in most cases very remote.
The first aspect to consider when it comes to keeping our plants attractive is their health, that is, their vitality. A plant's vitality is measured in how well it is able to function within the limiting effects of its cultural surroundings. While the word "health" covers a LOT of territory, the 3 primary cultural influences that most affect the appearance of the plant are soil choice and watering habits, light, and nutrition.
Root health is key to an attractive plant. There is no chance for a healthy plant unless the root system is healthy, so find a thread that addresses how water and soils interact & gain an understanding of that relationship so you can consistently provide a healthy root environment. Learn to do full repots instead of potting up. Find a good thread about nutrition and establish a GOOD nutritional supplementation program that ensures your plants are getting all they require. Resist adding a little extra this and that - TRUST your program once you're sure it's supplying all nutrients in a favorable ratio. Light is very important, but not something we can change much. You either have good light or you don't. Many of us supplement lighting where we can. It's important to understand that lack of light can be extremely limiting. Do the best you can. Ask, if you want referrals to threads that cover soils & nutrition.
Note that all issues so far relate to health/vitality. If you maintain the considered effort to ensure your plant's good health, keeping it as your focus, the rest will take care of itself - until it comes to controlling your plant's growth habit in order to keep it looking attractive. If you think a 25 ft long vining plant that winds around itself half a dozen times before it strikes out across the mantel and back, or perhaps that Ficus that has hit the ceiling 3 feet ago, or even the Aeonium stalk bearing that single rosette on the end of a 2 ft stalk you have lashed to a stake illustrates growing prowess, there's no need to read on. ;-)
The growth habit of some plants is such that they offer little opportunity for guidance toward a more attractive appearance, but many plants DO. In fact, many plants require regular intervention if the grower has any sort of vision of how they want that plant appear, or they require intervention to return them to something you feel is appealing to the eye - rejuvenation. We all approach growing differently, but if I have a plant that doesn't look good - that doesn't have eye appeal - you can bet I have a plan in place to change that. For me, because I'm able to maintain a high level of vitality in practically everything I grow, it mostly comes down to pruning and understanding how to manipulate plants so the will of the grower instead of their growth habit prevails.
There are two hormones (growth regulators) that control how a plant grows and how it responds to pruning. Understanding the relationship between these hormones forms the basis for all intelligent pruning; that is, all pruning with a plan. First though, I want to touch on something that is an important consideration that has to do with vigor.
The most vigorous part of your plants is and remains the tissues closest to where the stem transitions to roots - the basal part of the plant. Plants do not age like people, they age ontogenetically as opposed to chronologically, like us. W/o getting complicated, this means that a plant's tissues tend to retain their ontogenetic age. The tissues nearest the base will always be youngest (ontogenetically) so they retain their juvenile vigor. That is why when you cut many plants back to the ground, they virtually explode with juvenile growth. It's no accident that this type of pruning is called rejuvenation pruning and can be applied to a significant % of house plants.
Note too, that pruning roots back closer to the junction between roots and shoots has the same rejuvenating effect on both roots AND shoots. Many think it's utterly taboo to fuss with a plant's roots, but they couldn't be more wrong. Root pruning and full repots, including removal of all soil as opposed to simply potting up, have a rejuvenating effect and are an important part of long term maintenance - a far superior approach to potting up. We can talk more about that if there is interest - especially about timing repots.
I mentioned that there are 2 growth regulators that primarily determine how a plant grows. Auxin, is produced primarily in apical meristems (the growing tip of a stem or branch), but is also produced in leaves. Its movement in plants is 'polar', which means that it moves downward toward roots. As it moves downward, it prevents buds proximal (closer to the roots) to the growing tip of the branch from becoming active.
Cytokinin is the other hormone we need to consider. It is produced in the roots, its movement is also polar - upward. It tends to stimulate growth of dormant buds. It's easiest to understand the relationship between these two hormones as an antagonistic one. Think of them as always fighting against each other for control of how the plant grows. If auxin is dominant, the plant grows long as it suppresses the buds that turn into lateral growth and make the plant bushy. If cytokinin is dominant, we get a bushier plant with more lateral branching. In most plants, auxin is the dominant growth regulator ...... but it doesn't HAVE to be.
As the grower, WE can take control and tip the balance in favor of more lateral branching and a fuller, bushier plant by reducing the downward flow of auxin that suppresses back-budding and allows cytokinin to stimulate buds to grow. We do this by pruning or pinching. In the case of very vigorous material, we can also even go as far as partially or completely defoliating to eliminate nearly all auxin flow and maximize back-budding. This is an important trick in the tool box of bonsai practitioners who use it to increase 'ramification' - the number of leaves and branches. Pruning and pinching simply removes the apical meristem where most of the auxin is produced, which forces back-budding.
Pruning and pinching permanently truncates growth of each branch pruned or pinched. That branch can never extend again. Usually, the first bud proximal to the pruning cut becomes the new branch leader. This is an important consideration because we can use the information to determine the direction of the branch. If we want the branch to grow left, we truncate it just distal (further from the roots) to a left facing bud or leaf - the opposite for right. When you're pruning your branching plants, try to prune back to a downward facing bud. Upward facing buds tend to produce vertical growth and can spoil appearances if allowed to become the new leader.
These practices can be applied to most of the vining or branching plants we grow. Pruning and pinching isn't difficult, and the response is very predictable. The grower just needs to understand the options and be confident enough in how the plant will respond to make a plan and take the leap.
Here are just a few plants with growth habits and appearance were dramatically altered by selective pruning or pinching: