Some of my Prunus lusitanica (Portugal laurel) shrubs are changing the color of the foliage and stems. Normally the leaves should be dark green and the stems are a dark cranberry red. The soil here at the coast is very sandy. I have put composted manure (the type from bags), fertilized them, and added a bit of lime to the soil around the trunk and close to the root zone. I have not seen much of a response. Do you know what is the optimal pH for Prunus lusitanica? I am concerned about these shrubs because I just planted them last summer.
Prunus lusitanica tolerates a wide variety of pH and moisture levels in soils. See California Department of Forestry SelecTree webpage about this plant.
According to the webpage of a local Seattle garden writer, the leaves do change color slightly, acquiring a bluish tinge in late fall to winter. She also says that Prunus lusitanica does not like wet feet.
What colors are the leaves turning? You might consider testing the soil, to make sure things are not out of balance. Here is a link to the Miller Library website’s links about soil testing.
Is it possible that the bagged manure was still hot, that is, not fully aged? If so, that could cause problems.
You might also bring in photographs or sample leaves to a Master Gardener Clinic for diagnosis. You can locate a Master Gardener Clinic within Washington State at this website.
I have a small rooftop plant bed that’s full of moss. Is that an indication of sour soil, and if so, can it be sweetened with Dolomite lime?
Moss is often simply an indication of a shady site or compacted soil, but can also be an indicator of low soil pH (i.e., acid soil). I wouldn’t recommend adding lime without doing a soil test for pH (you can buy an inexpensive kit at most garden centers), and without considering the pH needs of the plants you have in the bed. You would not want to increase the alkalinity of the soil if your plants are acid-loving.
You may find this link about moss growing in garden beds (from Oregon State University) of interest. Here is an excerpt:
“Mosses grow in garden areas for the same reasons they grow in lawns: for example, deep shade, high acidity, poor drainage, and soil compaction. As in the lawn, mosses do not compete with other plants. Rather, they establish in bare areas where conditions are favorable (Cook and Whisler, 1994).
Mosses have not been shown to hinder the growth of garden plants or trees. Reasons for removal are generally aesthetic. But aesthetics are in the eye of the beholder, and mosses are commonly viewed as positive features in landscaping. For example, traditional oriental gardening holds distinctive roles for mosses (Japanese Garden Society of Oregon 1996; see also Encouraging Mosses). Furthermore, in some situations mosses may help reduce moisture loss and crusting on soil surfaces.”
Successful gardeners know that healthy soil translates to healthy plants. See the guide to soils and fertilizers for the home gardener from WSU Cooperative Extension.
A list of the best books, articles and websites on soils, soil amendment, composting and mulching.