Jennifer Schultz Nelson
Extension Educator, Horticulture
I know in my head that it usually takes a period of time for a plant to develop a problem. But it seems to me that one of my little dwarf Alberta spruces turned entirely brown overnight. Thinking it was a goner, I figured it was time to shop for a new tree, and also time to figure out what happened to the brown one.
Dwarf Alberta spruce, Picea glauca var. Albertiana 'Conica', is a dwarf cultivar of the Alberta White spruce, Picea glauca var. Albertiana. The spruce genus, Picea, is derived from the word pix or pitch, meaning the sticky resin in the tree's bark. The species name, glauca, means "glaucous", in reference to the lighter color of the tree's needles as compared to other evergreens.
As an ornamental tree, dwarf Alberta spruce is prized for its compact pyramidal growth habit, and tiny half-inch needles which are densely packed on its branches. It is also a very slow grower, only two to four inches per year. This makes it suitable for container plantings, as it will not outgrow its container very quickly.
Since dwarf Alberta spruce has a very distinct, pleasing pyramidal shape, it lends itself to formal landscape designs. It is a great choice for lining an entryway or other focal point in the landscape.
At maturity, dwarf Alberta spruce will reach about ten feet tall by three feet wide. My parents have had two dwarf Alberta spruces as long as I can remember—they are full sized now, but looking back, its fun to see how their growth progressed along with my sisters and I in family pictures.
One great asset to having a dwarf Alberta spruce in the landscape is that they very rarely need pruning. They naturally maintain their shape. Their needles are thin, but grow very densely on the tree, giving it a very solid and full appearance. The branches also persist all the way to the ground, without the lower limb dieback common to some evergreens as they age.
There is one significant time when a dwarf Alberta spruce will need pruning. The dwarf Alberta spruce is essentially a mutant of the much larger Alberta White spruce. Occasionally, especially in older trees, new growth on branches will change in appearance, the needles appearing much longer and growing much faster. These sections are called "revertants" meaning that on the DNA level, cells are losing the dwarf mutation and reverting to the Alberta White spruce form, the "original" or "wild type" form of the plant.
If you wish to keep your dwarf Alberta spruce a dwarf, any revertant sections need to be removed promptly. Prune just below the area where the revertant branch form begins.
Just as an aside, revertants are common in many other ornamental plants. It is commonly seen in plant cultivars valued for their variegated or novel foliage. I have a hosta in my garden with some novel variegation that I love—half of the plant has come up solid green this year. I love the wiegela 'My Monet' for its pink and cream variegation, but I have to keep an eye out for the occasional solid green branch that pops up. Sometimes reversion occurs so frequently, it makes a cultivar unmarketable. Mostly it's just a random curiosity.
Dwarf Alberta spruces prefer to be planted in full or partial sun with very well-drained soil. They will not tolerate wet feet. Unfortunately, they are also not very tolerant of urban environments. Pollution, road salt, and high heat are all not well-tolerated by this tree. This is probably why many trees never reach maturity—city life does them in!
As far as my poor little brown tree, it looks like he's a victim of spider mites, and extremely common problem for dwarf Alberta spruce. Oregon State University sources say that when spring and summer is very wet, mites are more likely to be a problem. Spider mites prefer hot dry conditions to flourish, so why would a wet spring like we've had predispose my tree to their infestation?
The answer is stress. Generally speaking, a stressed plant is far more likely to be affected by pests or disease. Dwarf Alberta spruces are stressed in extremely wet conditions—it is no coincidence that I first noticed this problem a couple of weeks ago, after we recorded 10+ inches of rain at my house.
To confirm the presence of spider mites, place a sheet of white paper beneath some branches and shake the branches over the paper. If you see tiny red specks that are moving, you have the mites.
There are several methods for controlling spider mites on dwarf Alberta spruce. The non-chemical method is to use a forceful stream of water to knock the mites off the tree. Since dwarf Alberta spruce hates wet feet, this may not be the best choice.
Chemical controls are numerous, and include the active ingredients bifenthrin, dicofol, and fentabutatin-oxide. Other chemical choices include canola, clove, cottonseed, petroleum or sesame oils, and insecticidal soap.
I thought the tree was totally dead, so I didn't even think it was possible to save. I looked closer at it yesterday, and it has new growth at the end of the branches. Despite the extensive needle loss, if I can save the tree the new growth should disguise this. My parent's trees have had spider mites over the years and have consistently recovered from them, so I'm hopeful mine will survive.