Rosemary Dies When the Soil Is Kept Wet

Q. Last January we had our yard professionally landscaped which included 4 rosemary bushes near a west facing block wall. The bushes were thriving, doubling in size until the middle of summer. Unfortunately, three have died and the fourth nearly gone. Can you offer some suggestion as to how I can stop this problem from spreading?

Rosemary is a tough plant. It can handle some very tough locations. But it cannot handle soil that is constantly wet. The roots of this plant suffocate easily in wet soils, particularly during the heat of the summer.

A. Rosemary is susceptible to root rot diseases if the soil is kept wet. This can happen if it is watered too often, planted in soil that does not drain water easily or covered in rock so it never dries out. Plant death from root rot is frequently seen during the heat of the summer. This is not a problem that should spread beyond the rosemary.

This picture of Rosemary was taken in the middle of winter. It's one of those plants that blooms a lot and attracts honeybees when there isn't much else around that's flowering. It's a good plant to have near fruit trees that are early bloomers in the spring. It will handle about the same frequency of irrigation as fruit trees.

            Landscapers set the irrigation clock to water frequently after planting. This can be important during the first two or three weeks while plants get established in their new location, but irrigations should be less often once the plants begin growing. They assume that someone will adjust the irrigations later and not let them run daily.

This is what Rosemary will start doing when it's getting watered too often. First you see a small stem start to die, and then the center starts to die and then the whole plant dies. You drowned it. It's dead.

            Some soils do not drain water easily. In these soils it is best to plant on raised mounds or mounded soil so plant roots can grow into the surrounding dry soil in these raised areas. Use a similar soil to the existing one, just amend it with planting mix or compost.

            It is common for landscape soils to be covered with 2 inches of rock. Because the surface is covered in rock they are called “desert landscapes” which is arguably not true. Keep rock or any kind of surface mulch at least 6 inches from the base of the plant when it's young. Surface mulch will keep the soil from drying out and may contribute to the loss of plants if they are watered frequently.

            What to do now? You will probably plant again. Don’t plant in the same holes because the soil in these holes have a buildup of disease organisms. Plant at least 12 inches from these locations and reroute the irrigation. Water them daily the first week to get them established and then begin watering less often. In this case too much applied water is not important as how often it is applied. Water less often but give  them a generous amount when you do.