- Written by Kevin R. Lee Kevin R. Lee
- Published: 20 January 2020 20 January 2020
The cherries are stone fruits; the fleshy coating that we eat covers a single hard stone which is the seed. Their cousins are plums, apricots, peaches, almonds.
The Evans cherry, Prunus cerasus, is an excellent small red cherry-producing tree that we will talk about later. The Evans and most of the edible shrubby cherries will be dealt with elsewhere in the chapter called Hardy Prairie Fruit. I will include here the Mayday, Schubert, Amur, the native chokecherry and the pincherry.
The Mayday, Prunus padus, is another extremely popular tree, for good reason. It is usually the harbinger of spring, first to leaf out, followed shortly by its incredible white cloud of blossoms covering the tree. In maturity it can be a large tree. I once saw one in Crescent Heights standing at about 60 feet, but 30-40 feet is more common. With grey pewter bark and usually multi-trunked, it makes a good, quite wide shade tree. With dense growth pattern by nature, all of the cherries like to be thick. Overpruning, too much thinning is a common mistake. Each type of tree is best left to its nature. Pruning a cherry that opens it up like a poplar is a mistake and a stressed tree. So the idea of crossing branches always being removed does not work with the cherries; nature knows best.
The Swedish Mayday is a somewhat smaller variety with pink flowers, very nice.
Maydays are susceptible to sun scald. Many trees have large lesions of dead bark on the sun side. Although not lethal, they don't help. If possible, plant a small shrub between the trunk and the sun; this will help a lot.
Maydays are the most affected of the cherries by the black knot fungus, Apiosporina morbosa to my pathologist friends. Like all fungi, it takes its energy from other living and dead things. Once mature, it produces spores and it is when one of these invisible little hooks lands on your tree that the trouble begins. During the first year, you won’t notice anything, as the fungal structure gets a good hold inside a branch. After infection in the spring, the immature swollen knots usually appear in the fall. They are then dormant as they pass through the winter. Next spring, they resume growth, getting longer and thicker. Then the bark will split and the classic black knot becomes visible. The mature spores on the surface of the knot are released in great number the next spring, completing the cycle.
There is no cure for black knot, other than regular inspection followed by pruning. Working with this fungus through the years, I have made some interesting observations. Most of the black knot in Calgary has a physical limit to its growth capabilities. While completely wrapping around and killing smaller branches, when the fungus sets up on the trunk of a tree, it usually can’t reach all the way around. In this case, liquid transport has not been interrupted and the branches above are full of healthy leaves. When I find one of these, I turn my saw on the knot itself, shaving away at it. I try never to harm the margins where the knot meets the uninfected tissue. Sometimes this has good results.
The Schubert cherry, Prunus virginiana ‘Schubert’, is rivaling the popularity of the Mayday. With its much lower black knot susceptibility and tighter oval form the Schubert may be our best chokecherry. It flowers early like the Mayday. Afterwards the first young green leaves start to turn purple. Purple is the summer color and only the latest young leaves on shoot extensions appear green. For pruning , sometimes a little thinning is needed, especially when young trunks start to braid, but mostly the Schubert requires only interior dead-wooding.
The Amur cherry, Prunus maackii, is another import from Asia. Amur is a common name in western horticulture, as many plants from that region found their way to the harsh climate of western North America. The Amur river is located in NW China and forms some of the border between China and Russia. This is a beautiful tree with copper colored exfoliating, naturally peeling bark, green leaves, white flowers and small black cherries. Be careful when choosing your Amur. Many of these young trees exhibit co-dominant crotches that are highly susceptible to splitting from the weight of early and late snow storms.
Cherries do not get fire blight. Pseudomonas, another blight forming bacterium, preys on the cherries with similar symptoms and sometimes lethal results. This disease is the sneaky, quiet one. A bacterium like fire blight, it affects a different group of hosts. Similar in its methods to fire blight, it attacks the rose family stone fruits that are immune to fire blight: cherries, plums, apricots. When these trees are infected, usually one of the symptoms is gummosis, which is an amber-like deposition of hardened sap that collects near cankers. The other commonly affected hosts here are lilacs. They are affected with classic blight symptoms, wilted discoloured flowers and leaves.
One favourite tree that can be outright killed by Pseudomonas is the beautiful Amur cherry. Last year, a homeowner noticed some wilting on her 40-foot Amur in the McKenzie Towne area. Several calls went out, some time went by, and some misdiagnosis occurred. In about three weeks, the tree had gone from a couple of wilted looking branches to being overwhelmed by the disease. Removing it quickly to avoid spreading the disease was the only option.
Lastly, let’s turn to the native cherries, the chokecherry and the pincherry.
The chokecherry, Prunus virginiana, native throughout most of Canada, is a tough beautiful clump shrub. It can grow to almost twenty feet. It’s highly recommended for smaller properties, a good screen for privacy, with, lots of small white flowers and delicious black cherries. The cherries are an acquired taste and the word choke in the name refers to the astringent aftertaste. They have been used as a fruit source for wine, and also make good syrups. Their only problem is black knot, easily identified and removed once the leaves have fallen.
The pincherry, Prunus pennsylvanica, is a small tree that should be on every small property gardener's list. With an oriental-cherry-looking bark, small white flowers and beautiful small bright red cherries, it's a winner.