This will not replace Cass Turnbull’s Guide to Pruning, which is the bible for pruning. She revises it every few years and it should be in everyone’s library. In it she gives details of how to prune specific plants. Cass calls her book the “what, when, where & how to prune for a more beautiful garden.” Also, if you ever get a chance to hear her speak, don’t pass it up; in addition to valuable information, she has a wonderful sense of humor. I, on the other hand, will try to give you some general guidelines that may keep your plants alive and even healthy.
When it comes to pruning, the one-third rule is probably the most valuable: ‘At one time, never remove more than 1/3 of a plant. ‘For example, you have a large evergreen that is taking up most of your lawn and you would like to remove the lower limbs to regain some of your yard. Estimate how tall it is, then go ahead and remove all the bottom limbs, from the ground up, to 1/3 of its total height, leaving 2/3 for the health of the plant. Plants like roses and hydrangeas will become crowded with stems. Going to the base of the plant, remove old growth, highly branched stems, and crossed stems, but not more than a total of 1/3 of the stems. For shearing a hedge: Even though you will be working from the outside, do not remove more than 1/3 of the hedge. The same 1/3 rule applies to root pruning of potted plants.
In addition to roses and hydrangeas, let’s look at shrubs like flowering quince that can get 10 feet tall. Go ahead and remove 1/3 of the old, crossed, or unhealthy stems from the center, cutting them at the base of the plant. This will improve air flow and discourage mildew. Now lower the outer stems, being sure to choose a cut above an outer- facing bud. You may also want to vary the height of the outer branches to give the appearance of a more natural growth.
It is easier to keep trees small than deal with overgrown ones. Again, from smaller trees, remove some center branches and snip the ends of others, do not shear, and your tree will maintain its shape while staying small. For large, overgrown trees be ruthless. You are going to have to cut large limbs. Again, do not shear, but cut each limb individually. When you come to the top of the tree cut it at an angle, as a flat top will collect water inviting mold and disease and the tree will die.
Shearing can lend a touch of formality to the garden. Again, it is easier to keep a small plant small than reduce an overgrown one. For example, Japanese Spirea grows in a globe shape, but by shearing the ends the shape becomes more pronounced. For new hedges, the first few years don’t take off much, just nip the ends into the shape you are going for. If you want a larger hedge, trim a few inches off the tips to stimulate growth of upward and side branches, making a thicker, denser plant.
An overgrown hedge can be quite a challenge. In a straight line, at the ends, place stakes that are taller than the hedge. Run a line between the stakes at the height and width you want the hedge. A line level helps for straight-cut edges. The hedge needs to be wider at the bottom than at the top so sunlight reaches all the leaves. If you don’t do this the plant will eventually drop its lower leaves. Rule of thumb is that the bottom should be at least four inches wider than the top depending on the total height of the hedge. You may also need to pre-prune large branches (anything larger than a pencil) with clippers. Most important, you will need to shear more than once a year to keep the plant looking good and healthy.
Be brave. It takes courage to prune.