The aspen could have been a strong contender for our choice of national tree. There are only three regions in Canada where it does not proliferate, the west coast, the treeless north and the driest heart of the prairies, Palliser's triangle. There are several natural forms that represent the aspen's struggles in different environments. High on mountain sides they assume a krumholtz look, in sheltered bowls and valleys you find pure stands of 80 foot trees, and on the prairie the ubiquitous aspen grove. These groves are usually clones from the starter tree, now long gone from somewhere in the middle of the grove. Indeed, these clones are the largest living single organisms, meaning that all parts of the grove, roots, trunks, and branches have the exact same genetic make up. There is rumored to be a grove in Colorado over 200 acres in size, the largest living organism ever to grace this planet.
In the garden it is almost impossible to duplicate the native grove, but all attempts are worth it. Because most natural groves increase from shoots forming from outlying roots, the young trees have their roots and water supply already in place, not so when you buy single trees in containers. These delicate trees require a lot of water until they establish, and in the first years they usually grow much more rapidly than their native cousins.
There is a fine line here and I have always erred on the side of caution with my aspens, so I have beautiful young trees in my grove, but they are much leggier that those in a native grove. You can't take new young single trees, plant them and walk away; without regular watering they will quickly dry up. This is the trade-in off bringing the wild into your garden. Once established, an aspen grove makes a powerful statement in the garden and when they have all connected underground they form a tight tribal mass. It is at this point that they will start to produce new shoots from the roots. This is natural and healthy, showing that the grove is now functioning as a native grove should. If you get young trees growing outside the allowed space, just cut them back at ground level.
Another option with a group of aspens for size control is selective thinning. This is similar to the old European technique of copsing. By removing a larger tree you force the grove to speed up its production of new shoot trees. By cycling through like this you can keep a constant height and size to your grove.
I am on my second aspen grove in twenty years. When we moved we planted again and of the 50 or so finger size trees, some are now 15 feet high and growing.
Because the native aspen occupies so much territory in North America and is so prolific, it is a major food source for many insect predators, forest tent caterpillars being one of the most obvious. Most of these insects cause little harm. Occasionally aspen groves are defoliated early in the spring, then as the insects' cycle advances the trees form new buds and leaf out again. This is expensive for the tree but necessary. They need their leaves to produce the energy that the coming winter will require of them.
Fungal diseases also take their toll. Weak aspens are highly susceptible to cytospora canker and hypoxilon canker. Cytospora is recognized by greyish cankers, dead lesions in the bark. Hypoxilon is identified by a bright orange striping on the bark. This is nature's way of cycling through and reusing the weak tree in a grove.
In your own grove this is a little more distressing, and if one of my aspens got hypoxilon I might be tempted to remove it to save the others. A first step could be to use a knife and remove all the affected bark. This might stop the infection; a terrible wound is sometimes better than removal.
Another insect that is common in aspens is the poplar borer, a little-finger-sized larva that lives for four or five years inside the trunk. It always leaves a telltale brown sticky stain on the trunk. The hole in the tree where the stain originates usually has wet saw dust at the outer edge. If you see this begin on your tree, cut a coat hanger and insert the wire into the hole. you may be able to kill the larvae this way.
As with all of our tree friends the aspen has its share of natural problems. This is not a reason to discount it, but to realize that it is a serious survivor and whatever nature throws at the aspens they still flourish. On a cool quiet early summer evening just sit, and listen.
The other aspen is the Swedish columnar. It seems there are still a lot of misconceptions about this tree. Since it was introduced about 30 years ago, we can now take an honest look at its performance. Most of the information available still speaks of an approximate mature height of 45 feet. You can safely double that; I have seen numerous examples well over 45 feet. Opinions about its annual growth vary, but three to four feet seems most accurate.
There are claims that this is a non-suckering tree. These trees sucker profusely, in the lawn, in the neighbour’s property; wherever they can, they sucker. Sold as the answer to all the modern family’s tree needs, its performance is not consistent with its sales pitch. The only way to manage an unruly group is to treat them like a hedge, pick a height that still provides privacy, and remove the tops. This will force the trees to grow at an even faster than normal rate. It will also force them to sucker even more than they naturally do, just a lose-lose situation. Let’s raise our eyes from the rhetoric of nursery catalogues and take an honest look up at the trees. I would seriously caution anyone thinking of planting this tree. There are many better alternatives.