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It seems counterintuitive to cut off branches, leaves, or even roots to get larger, fuller plants. And yet, it’s one of the most important maintenance tasks for a thriving, healthy lawn and garden.
Pruning stimulates growth if it is done correctly. There are small nodes or regions along each plant structure that contain growth hormones, and if you prune directly above them with a clean, sharp tool, these hormones are triggered to repair or regrow plant tissue.
Let’s look at why pruning stimulates growth and how you can use selective pruning to control the shape and production of your plants.
How Pruning Stimulates Growth
Plants have small portions of tissue known as meristems. These meristems are responsible for all plant growth.
Meristems are pockets of cells that have an undefined future. They can become roots, leaves, flowers, stems, or any other tissue. Hormones regulate what kind of tissue the cells in a meristem will become.
There are three kinds of meristems (source):
- Apical Meristem. The apical meristem is found at the tip, or apex, of a stem, trunk, branch, or root. They are also found in leaf nodes. These are responsible for plants growing taller, longer, or deeper, and for leaf and flower growth.
- Intercalary Meristem. The intercalary meristem is mostly found in monocots (grasses) and is the primary reason grass can be mowed and regrow from the crown, or base.
- Lateral Meristem. The lateral meristem is found in the outer tissues of stems, roots, or branches. This meristem is responsible for girth, or a plant getting thicker.
The apical meristem releases a hormone that creates apical dominance. As the tip of a trunk or branch keeps producing new stem growth, and grows longer, a hormone is sent back down the branch or trunk that lets the other nodes know that their job is to create leaves, flowers, thorns, etc.
If the apical meristem is cut off, the hormone stops flowing. This can trigger nodes along the stem or branch to grow new stems and branches to add height or length.
Pruning can trigger certain hormones to send a message to meristems to grow new plant material. The most common way to do this is to cut above a leaf node.
As the cut heals, the meristem that would have produced leaves or flowers is now triggered to grow new stems. The nodes along the branch or stem may also begin to grow new branches to make up for the loss of the apical meristem.
How to Prune to Encourage New Growth
Why is it so important to understand meristems? Why can’t you just cut off a branch and hope for the best?
Each branch, trunk, or stem has nodes and internodes. A node is a point of growth, and an internode is the part that is in between the nodes.
If you cut in the middle of the internode, it will be too far away from the node to heal. If you cut into the node, the meristem is no longer protected, and it can’t heal.
Healing is what triggers the stem cells and hormones to grow new plant tissue.
When you prune, you must cut right above a node to encourage healing and trigger new growth. This is why most pruning instructions tell you to cut right above a leaf or leaf bud and to cut at an upward angle away from the leaf.
This angle protects the meristem and minimizes the risk of infection.
If you cut in the internode and leave more than ¼” of stem tissue above the node, then the remaining stem will begin to dry out or rot. This leaves the stem open to infection, and the node below will die.
When you prune a branch or stem, follow these steps:
- Decide how long the branch or stem should be, and find the closest node.
- Hold your pruners 1/8” – ¼” above the leaf node (larger nodes need more space), and angle the pruners up away from the node.
- Cut off the branch or stem with one quick motion. You must have sharp pruners, or else you risk jagged, torn tissue.
Proper placement is only half the equation for encouraging growth. If you prune during the wrong time of the year, you may do damage to the node and inhibit new tissue.
Before you prune, look up the yearly maintenance information on your plant to see what you should do during each season. Most pruning should be done spring-fall for deciduous plants.
How to Control Growth with Pruning
Light pruning controls overgrowth, removes damaged plant material, and thins out suckers or watersprouts. This is appropriate for most shade trees, shrubs, and woody perennials to keep them healthy and contained.
However, pruning also gives you control over shape, flower and fruit set, and root depth. If you want to go beyond light maintenance and improve the overall health and shape of your plants, you can do more detailed pruning to manipulate the meristems and hormones.
Directed, purposeful pruning will increase flowers and fruit set, and it can also place flowers and fruit in more desirable locations on the plant.
Age of the Wood
Many fruit trees, shrubs, and vines produce flowers and fruit on growth that is a certain age. For example, apple trees produce fruiting spurs on wood that is 2 years old or older.
Apples should be pruned to encourage some new growth each year, but spurs can fruit for 6-10 years, so you should avoid heavy fruiting so you don’t hurt production.
Peaches, however, fruit on first-year growth. You can prune peach trees heavily, because they don’t fruit on wood over 1 year old. Heavy pruning encourages lots of new growth, which will produce more flowers and fruit than if you didn’t prune at all.
Identify the shrub, tree, or vine you want to prune, and look up what age the wood needs to be in order to get flowers and fruit.
If your plant flowers/fruits on first-year growth, you can prune heavily and try to encourage lots of new growth.
If you plant flowers/fruits on older wood, try to identify the wood that is too old for production and remove that first (if it’s not structural), and remove other stems/branches methodically to preserve older wood each year.
Most flowers and fruits need light, which means your pruning should focus on removing interior branches to aid airflow and light penetration.
Start pruning inside the plant before you move to the outer branches or stems, so you can maintain a full shape that provides a healthy environment for flower and fruit set.
Some plants have alternating leaf patterns while others are opposite. This matters when you are shaping your plant.
Alternating leaf patterns have alternating leaf nodes, so if you cut above a node, one stem will grow from the node and it will grow in the direction the leaf would have grown.
Opposite leaf patterns have opposite leaf nodes, so if you cut above them, you will have two stems, one from each node, and they will both grow away from each other in the same direction the leaves would have grown.
If you prune a plant with an alternating leaf pattern, make sure you choose a node that points in the direction you want the new stem to grow. If you want it the opposite direction, pick the node above or below and prune there.
If you prune a plant with an opposite leaf pattern, you can create a very full, bushy outer growth by leaving both nodes and letting them grow lots of small stems with new leaves.
However, if you want to shape or direct new growth, simply rub off a node and allow the remaining node to grow a new stem.
Roots will respond to any pruning method by growing deeper and more fibrous. As plants are cut and triggered to heal by certain hormones, roots get the message that something is stressing the growth above ground.
Roots respond by growing a more complex root system so they can access more water and nutrients to help the plant maintain new growth and withstand the perceived threat.
You can also prune roots directly with shovels or pruners, but this is only recommended for some plants under certain circumstances.
Pruning is an important maintenance task that requires basic knowledge of plant anatomy. It is better to let a tree or shrub grow naturally than to prune without understanding how the plant will respond.
Sharp pruners like the Felco Pruning Shears (link to Amazon). are a must for clean, consistent cuts.