The flowering crabs are one of the most diverse and well-loved groups of trees. For sometimes two weeks the city is full of beautiful white, pinks, reds and purples, many times so thick that the tree itself cannot be seen. Ever popular, the choices through the decades, now many of them failures or obsolete, would be in the hundreds. As I roam around the city I always find distinct varieties, many of their names now lost. A thorough review of them all would be an exhaustive work, and I doubt anyone knows all of them.
For convenience I put them into three handy groups, the whites, the purples and the greatest group by number, the Rosy blooms, which contain all the varieties of pink. Culturally they mostly behave the same. They thrive in good loam, slightly acidic if they can get it, though there is less of a chance of that in Calgary. They like moist well-drained soil. All are susceptible to fire blight, a powerfully destructive bacterial disease. They can also suffer from apple scab (mostly on wet years), powdery mildew, apple/juniper rust, cankers and oyster shell scale.
As to pruning, it is best to start with a wide, open framework of large branches off of the main trunk. If these are all of sound attachment, they should last a long time. They do not top well; this is a direct route to a tangled disaster, which takes some doing later to repair. Although it seems to create a repetitive cycle, pruning the inner water sprouts, suckers, shoots (they go by all these names and more), is the easiest way to show off the awesome beauty of these trees. Moving around a well-pruned tree, the play of light is a thing to see.
Below are lists of some of the common varieties sorted by color.
- Dolgo: disease resistant, apples large enough to make a mess, great jelly.
- Siberian crab: small yellow apples.
- Rosthern: a columnar Siberian, extreme fire blight susceptibility
- Red Jade: named for the beautiful fruit.
- Spring snow: flowers but no fruit
- Thunderchild: a classic, great tree, purple leaves.
- Kelsey: double flowers
Pinks (Rosy blooms)
Older varieties :
- Makimik, reddish
- Royalty, reddish
- Strathmore, susceptible to powdery mildew
- Royal beauty, weeping
- Pink spire: copper leaves
- Purple spire: columnar
All of the above are good varieties for the Calgary area, but all are blight susceptible to some degree; inspect each week during the growing season. Any branch in the sun that is not broken but exhibiting dry red leaves probably has blight. That branch should be removed, a foot or so back into healthy tissue for your cut.