Question: Um…why is there is a huge tree growing out the side of my dwarf Alberta spruce???
We have a row of dwarf Alberta spruce trees planted in front of our home. One looks like a Christmas tree is growing out the side of it. It’s completely different than the rest of the tree and much bigger than the original dwarf tree. What’s going on?
Answer: We get quite a few calls during the year where clients say, “There is something growing out of my tree that’s different”, or “There’s a tree growing out of my tree.”
Although it looks strange, it’s actually a normal process called genetic reversion. Basically, the tree (or part of the tree) is reverting back to its original form.
In the case of dwarf or small trees, the newly reverted branch grows significantly faster than the host tree (just as the full sized version normally would). In needle-bearing evergreens, it also reverts back to a full-sized needle versus the small needles found on the dwarf species.
To understand why reversion happens, we need to look at where the host tree came from.
Where do dwarf trees come from?
Dwarf Alberta spruce showing reversion to a full-sized white spruce
Many ornamental tree cultivars, especially dwarf varieties, are derived from naturally-occurring genetic mutations.
Nurseries, biologists and botanists look for abnormal growths, patterns and colors on trees. They then use that mutation to help develop new cultivars or sub-species through techniques like cross breeding or grafting. The resulting tree often looks very different from the original parent tree.
In the case of the Alberta spruce (Picea glauca ‘Conica’), two Arnold Arboretum botanists found the dwarf in 1904 as a naturally occurring mutation of a white spruce. At the time, they were waiting for a train at a railroad station in Alberta, Canada – hence the name Alberta spruce.
This new species stemmed from something called a witch’s broom where certain shoots or branches grow as a genetic mutation with small, dense needles and very slow growth. This particular one can be found on white spruce and Norway spruce trees.
So if you see a large spruce tree with a small section that’s very dense and dark in color (it looks quite unlike the rest of the tree) or if it looks like there’s a nest in the tree, it’s probably a witch’s broom.
Which trees are most likely to revert?
Reversion can happen in many species but in Danbury and surrounding areas we mostly see it in dwarf Alberta spruce trees. Roughly 5% to 10% of Alberta spruce will eventually revert to the white spruce from which they originally came.
Don’t worry though – it’s not “contagious” and won’t spread to any other Alberta spruce in your yard.
As a side note … Technically, the dwarf Alberta spruce isn’t a “dwarf” tree at all – it’s just very slow-growing. Be aware that Alberta spruce can grow to 10–15 feet tall and 6–10 feet wide so be careful not to plant it too close to walkways, structures, decks, etc. (see our article on planting the right tree in the right place)
What should I do if my tree starts to develop a genetic reversion or mutant growth?
You can generally prune out a reverted branch or stem by cutting it off right where the abnormal growth starts.
It’s important, however, to do this as soon as you notice the unusual growth. Because it grows much faster than the host plant, a reverted branch or stem can quickly take over the entire host. Plus, if it’s grown quite large, removing it will likely leave a large gap that will disfigure the tree and/or take years to fill in.
If you’re unsure about whether your tree has reverted, give us a call at 203-240-1302 for a consultation.
