Aside from, “How do I get deer to stop eating my flowers?” the No. 1 question people ask me is, “When is the best time to prune my [fill in the blank]?”
My girlfriend picks on me because I usually give the standard expert answer: “Well that all depends.”
But it does depend. It depends on what you are trying to accomplish and what plants you are trying to accomplish that with. But here is an easy general rule of thumb to follow that will serve you well 99 percent of the time: If you want to promote growth, prune in the winter; if you want to inhibit growth, prune in the summer.
When I say this to the uninitiated I often get a quizzical look, and I understand that. It is counterintuitive to cut something off to make it grow, but really it is a simple concept to wrap your head around.
In the winter, most plants are dormant. They are storing all their energy in their roots, where it is safe from the hard freezes of the winter.
When you make a cut on the outer reaches of a tree or shrub, you are not taking all that much away in terms of energy. In fact, most plants have evolved to take winter damage, and they are ready to repair the wound easily and quickly come spring.
Not only is the plant best able to heal damage this time of year, the plant has all that stored energy in its roots ready to send up new growth.
When the sap starts flowing, the plant will send the energy to the dead end where you made the cut. When the plant realizes the branch is no longer there, the buds below the cut miraculously know to become new stems rather than just flowers or leaves. In this way you can remove one stem and turn it into two or more.
This is also an important idea to keep in mind when deciding where to place your cut. Of course, always cut above a bud; but by choosing which direction that bud is pointing, you manipulate the long-term direction you want the plant to grow in.
This is the key to growing large foundation plants, like magnolias or dogwoods, next to your house without worrying about them rubbing on your gutters or hitting your windows. It takes years of deliberate pruning, but you can steer their growth.
This is much easier to do as your tree or shrub is growing. Header cuts, as they are called, are best done on new growth, no more than three years old.
If you make one of these header cuts on an older limb, you are liable to create two problems. First, the cut will not heal over quickly enough, and the limb will rot out and potentially make the whole tree hollow, creating a hazard for you later.
Witch’s broom is the other overly common problem I see caused by inept pruning. Witch’s broom occurs when an improper cut is made on a limb, and the tree’s natural response is to overcompensate by sending out bunches of new shoots.
The added weight of all these new shoots, coupled with the tendency of the stubbed limb to rot, has been the untimely death of many a landscape tree.
Do not stub your trees. If there is an unwanted limb — say it is hitting the house or in the way when you mow — cut it back clean at a joint, all the way at the trunk if you have to. The tree is better able to heal at a joint and will send its energy elsewhere. You will avoid the ugly stub, the potential for rot and the ever-reoccurring witch’s broom.
However, in the case of perennial shrubs, you can use this tendency to your advantage.
For example, if you are trying to plant a hedge or you want your flowering shrubs to spread and become more bushy, you can cut them back hard in the winter. Many plants, especially the fast-growing ones, you can cut all the way to the ground. It sounds drastic, but as long as they are well-established, they will come back twice as thick in the spring.
At the top, I did mention using pruning to inhibit growth. It seems like that is what most people are after. Keeping your boxwoods small and round and the hedges nice and orderly seems wholly unrelated, but it is pruning, too.
If that is your goal, cut in the summer. You want to wait until the plant has expended all of its stored energy into this year’s new growth, and then cut it off. It always seems mean to me when I think about it that way, but it makes sense if your goal is to stunt growth.
I hope this clears up some of your anxieties about pruning. The first step is understanding the way energy flows through the plant from winter to summer; after that, it becomes second nature. It really is that simple.
So now is the time — before those buds really start swelling — to go out there, make some cuts and have fun manipulating the plants. Witness how the cuts you make today affect the plant’s growth for years to come. It is my favorite activity in the garden — it really is your best chance to shape and manipulate the landscape around you for years to come.