Pinching and Pruning - From the Plants' Perspective
I spend a lot of my time trying to look at life from a plant's point of view. While this can make me an odd conversationalist at times - it also makes me a better gardener. In so many ways, understanding what your plants need and why they need it can help you to have bigger, more beautiful plants - often with less effort on your part. Today, let's look at pruning, pinching and deadheading from the plant's perspective.
Root Shoot Ratio
A plant's roots take in water and nutrients from the soil to share with the rest of the plant. Leaves, too, take in important resources - sunlight and carbon dioxide (CO2) - to be converted into energy and shared throughout the plant. Leaves also release waste in the form of moisture and oxygen into the environment. Roots and leaves are equally important organs for a plant to survive and thrive. Neither can work long or well without the other being healthy and strong.
Each type of plant develops an ideal ratio or relative size between their roots and their leafy top growth that is ideal for that type of plant to be healthy and to thrive. This is called the Root to Shoot Ratio. While rose bushes might prefer a bit different root to shoot ration than bean plants or oak trees, each type of plant does have a natural ratio that suits it best. Very generally speaking, this ideal ratio is roughly 1 to 1, (or it is often expressed as 1:1) meaning a plant should have about the same mass of roots as it has top growth to support.
The importance of this root to shoot ratio is fundamental to the plant's health, and it is always putting energy into maintaining that balance. When something occurs to radically alter that balance, the plant goes into over drive to re-establish the balance. This is something gardeners use in order to get the results we want for our gardens.
Pruning, Pinching and Deadheading Plants
When we prune or pinch back plants to improve their shape or for better blooms and fruit, or deadhead for repeat blooming, we are taking advantage of the biological responses of these plants. When we prune or pinch back the leafy top growth of a growing plant, we radically alter its root to shoot ratio. The plants respond to this by quickly producing a large flush of new top growth in order to bring that important ratio back into balance.
Pinching and pruning work because plants respond to removed top growth by shifting their energies to quickly replace what was lost in order to re-achieve that important root to shoot balance. Plants have evolved this response to damaged top growth to deal with foraging animals and a changing environment.
Plants can be injured by a wide range of factors, and they respond differently based on different causes. And here is where it is helpful to consider things from the plant's perspective. If your leaves are damaged by a heat wave or drought, these are conditions that tend to last a while. There is no sense in replacing a leaf lost to high heat or drought right away - the new leaf is likely to be lost to the same continuing conditions, right? So the plant tends to regenerate new growth in these conditions rather slowly. But if you get chomped on by a passing goat, this is something to respond to immediately. Foraging animals tend to be on the move toward more food. They don't hang around a single plant. So rapidly replacing leaves lost to animal predation makes sense, just as waiting to replace leaves stressed by drought.
When to Prune and When to Repair
The plants' nuanced response to damaged top growth is how we decide when to prune back top growth, and when to leave stressed growth in place to recover. If your plant is responding to very temporary stimulus, like being shipped across country in a packing box, or its pot being knocked off the wall by a passing cat, you know the cause and the duration of the stress, and can help your plant respond to it by pinching or pruning back the affected growth. You know you won't re-package and ship the plant again, and the cat won't be back soon, so removing any damaged growth will tell the plant to quickly replace that growth with fresh new leaves. But if you live in an area with a lot of wind, and your young plants are stressed by this, it is best to leave the damaged growth in place, as this encouraged the plant to adapt to conditions you know to be on-going. When possible, we limit the plant's exposure to the sun or wind or cold conditions we want it to adapt to, gradually increasing the time of exposure. With seedlings started indoors, we call this process "hardening off".
We also deliberately choose what parts of a plant to remove and we time it for the purpose of getting larger blooms and better fruit. Pruning fruit trees, or pinching back and topping dahlias are good examples of this. When we pinch back, top or prune plants, we are using their natural response to foraging animals to work to our benefit. We specifically cut back their top growth where and when we need to in order to stimulate that flush of new growth exactly where and when we want it.
Pruning, pinching back, topping and even dead heading are all methods of strategically removing certain top growth to cause the plant to replace it with growth that will please us. Better understanding why the plant responds this way, and how it does so will better help you to learn and employ these techniques in your garden.
The timing and techniques used for topping, pruning, pinching and deadheading can vary between different types of plants. But the reason these different techniques are employed, and the reason they work is all due to the natural responses plants use to respond to different types of stress.
We will have many more articles looking at life from the plants' perspective. What do you think - did this give you a better - or different - understanding of how plants respond to stress in your garden? Feel free to drop a comment and let me know; or let me know if there is a specific thing you would like the plant's perspective on - I will do my best! :)
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- Kathleen McCarthy