Pruning should always be a very specific process.

The intent: What are you trying to accomplish?

The timing: What time of year is best to accomplish your intent?

The amount or dose: How much foliage can you remove without hurting the plant? How often will you need to prune this plant to achieve your goal? Are you willing to commit to managing the plant based on its reaction to the pruning – or otherwise not pruning?

The condition: Is this plant healthy enough that this pruning will not harm it?

The species: How will this particular species react to the pruning?

Knowing your plants and how each plant will react to your intent, timing and dose is hard to master. Different plants will react very differently.

American holly

Let’s take a look at each step in the process described above as it relates to pruning the American holly.

Intent: My intention for pruning these two American hollies is to keep them full, from top to bottom, for screening. (Photo 1)

Timing: Pruning evergreens in the late winter/early spring will encourage the most interior growth. Hollies are one of the best plants for reacting to the wounding, especially with reduction cuts (shortening the height or lateral growth).

Dose: Pruning in late winter enables you to be more aggressive. This is because you are capturing all the energy from the plant as it is preparing to push out new growth for the season. There is plenty of moisture in the soil as well.

Condition: These two plants were grown from seedlings. They are very healthy because I have been caring for them their whole lives.

Species: American hollies, and most holly species I have worked on, respond very well to reduction cuts. When you shorten the height or lateral growth, you encourage interior growth. Most evergreens will drop their second- or third-year leaves. This is the natural leaf drop. If you do not shorten or head back these branches, you often get long, leggy branches with growth only on the tips.

The pruning plan

With the pruning process for these hollies complete, I now have my plan. For some context, these plants have been pruned in this manner every two to three years for several years.

The specific plan is to prune these plants into a conical shape. The bottom branches are the oldest, so they should be the longest because they need the most light. The branches at the top of the plant are the youngest, and can be shortened aggressively. This conical shape also makes the plants less susceptible to snow load.

To further abate the risk of snow load, you will want to incorporate a little bit of a training prune to reduce multiple tops to different depths. This reduces the risk of the top splaying apart and breaking.

Reduction cuts

Making the reduction cuts at varying depths at the top and sides of the plant also encourages interior growth consistently throughout the plant. Even making proper pruning cuts (collar cuts) at the same level will cause the same effect as shearing, because it will only encourage growth on the outer shell, shading out interior growth.

Interestingly, even though you should have a very formal-looking plant when you are finished, because this tree was pruned in March, that look is fleeting. In late June, this plant will look like it was never pruned. That is another great benefit of late-winter pruning, if your clients prefer a less formal look. This type of pruning keeps the plant smaller, encourages interior growth so you always have something to cut back to and leaves the plant with a controlled but natural texture.

Natural or formal

Some people may prefer to leave their American hollies natural, leaving them to their own growth habit. This means the plants will be larger and more open, and sometimes showing a trunk. These natural American hollies are beautiful, too.

If you want your ornamental plants to have a more formal shape, it is best to prune them in the summer or fall, when their spring growth is complete. This is when you will receive the least reaction or sprouting.

Even though there are exceptions to all these guides, for the most part you want to avoid pruning aggressively in the summer or fall – especially evergreens, and especially if there has been a dry summer, due to the risk of winter desiccation.

Happy pruning!

David M. Anderson, CTSP and Massachusetts certified arborist, is a manager with Mayer Tree Service Inc., a 29-year TCIA member company based in Essex, Massachusetts, and is a member of the TCI Magazine Editorial Advisory Committee.