Arborvitae means Tree of Life. In this region, hundreds of the plants are sold at every garden center every year. They grow rapidly, and they are inexpensive. Best of all, dozens of varieties range in size from 25-foot tree to a 2-foot-tall ground-cover shrub and all sizes in between.
In the western United States, arborvitae is the most popular plant to shape into balls, spirals, pyramids and other fanciful topiary shapes. All sizes of the plant provide cover for birds, and quail are particularly fond of nesting in its dense branches. These are all the positive features.
Frequently, WSU Master Gardeners answer questions about arborvitae problems. The plant, which is a member of Thuja genus (think Western Red Cedar), prefers to grow in a humid environment. It is both hot and dry here. Watering more often merely rots the roots, a really common problem when the plant is used as a fence or screen at the edge of lawns. Or worse, the emitters hidden under the garden fabric get clogged, and the plant dries out totally.
The next most common cause of death is improper planting. This happens in two ways. First the shrub or tree is planted too deeply so that the part of the trunk under the soil rots. Arborvitae should be planted exactly as deep as it appeared in its original pot.
Another planting problem is that this shrub/tree grows rapidly in a very small container. Most people want the most “Bang for their Buck” and get the tallest one even if its roots are hanging out the bottom. A more moderate size in the correct-sized pot will create a faster-growing and healthier plant.
If the plant is root bound, often with roots circulating around and round the inside of the pot, the roots must be freed. They will not unwind on their own in the ground. Take the plant out of the pot and swish it in a large pail of water until most of the soil is washed off and the roots float free. Then dig a wide hole — not an overly deep one — and lay the roots out flat.
Plant arborvitae only in the soil already in your yard. If you fill the hole with compost or topsoil, the roots will not spread out in a healthy way into your native soil. Worse, most purchased soils hold water differently than your yard’s soil, creating potentially a swimming pool for the roots.
No matter what the label says, do not put the plant in the ground inside its pot. Some nursery labels say that the pot will break up — yes, eventually, but the pot will also slow down the growth or kill the plant.
OK, the arborvitae is thriving in your garden; you still have ways to kill it! The shrubs only need to be pruned once a year. I have noticed in March a number of landscape companies trimming and shaping up arborvitae hedges. The workers know they will have to be back in a few months for another trim job. Whereas, if the homeowner is patient and prunes at the end of April or the beginning of May after the flush of annual growth has appeared, she will only have to prune once. Linear plants need to be pruned so the top is about 20 percent narrower than the base so the entire plant has sunlight on it; otherwise, the lower needles turn yellow and fall off.
You cannot reshape an overgrown arborvitae all at once. It will take several years to trim it back to a smaller size. If arborvitae shrubs are cut back severely — more than 10 inches at one time — many times the shrub never recovers. So now you live with a pile of brown sticks with a bit of green fluff on them.
Spider mites love dry air; the humidity-loving arborvitae is plagued in our dry climate with spider mites that cause a yellowing and speckling of the needles. Aphids like the dense leaf arrangement growing on this plant, and it is a vector for stink bugs. Call the WSU Master Gardeners for information about the specific and particular time for treating these insect pests.
Finally, one more piece of bad news. Cold winters and cold winter wind can create dead leaf tips that limit the appearance of spring’s new growth. If you would like help with finding a variety of trees that could work like arborvitae, contact the WSU Master Gardeners at 667-6540 on Mondays and Wednesdays from 1 to 4 p.m.
A WSU Master Gardeners of Chelan County column appears weekly in the At Home section. Bonnie Orr is one of three columnists featured.