Pruning Boxwood and Rosemary Hedge Can Result in Disaster

Q. I have a neighbor concerned about his rosemary and boxwood hedges. He has been having trouble with the foliage browning and falling off. His landscapers recommend he cut them to the ground but he opted to cut them back by half instead and let them regrow. Can you tell me a little about these and your opinion about how to properly care for and what he should do to get them looking their best again?

boxwood

A. When rosemary and boxwood, or any plants for that matter, are continuously pruned with a hedge shears it causes them to get thick and bushy at the point where they are continuously sheared. This increases their density on the outer edges of the plants.

            Shearing causes the interior of the hedge to become very dark. This darkness cannot support leaf or new stem growth. The older stems on the inside of the hedge drop their leaves.

            All the new growth occurs only where it is sheared. Perhaps only an inch or two of the outer surface of hedged plants have leaves. The dark interior is leafless.

            If we cut too far back into the hedge we expose the older wood that has no leaves. The wood is alive, but without leaves. Once this interior wood begins to receive sunlight again, new growth will usually occur on the older wood.

            The rate of recovery of this older wood depends on the plant. Rosemary will come back faster than boxwood.

rosemary

            He will start to see growth coming from older wood exposed to sunlight as suckers. In technical terms we call this adventitious growth. Boxwood will do the same thing but it is much slower to react and fill in.

            If he is patient he will see new growth slowly fill in the canopy.

            If he had cut it back close to the soil surface, the same thing will occur on the Rosemary but it will be slow to grow back into a hedge. Boxwood will even be slower.

            In cases like these most people do not want to look at a hedge trying to fill back in and would elect to replace these plants.

            Once plants are cut with hedge shears for a couple of seasons they are very difficult to reestablish again as plants that are no longer a hedge. The interior of the hedge is just too woody.