The Rainier cherry, known for its golden-yellow skin, red blush, and intense sweetness, was developed at Washington State University in 1952 as a cross between the ‘Bing’ and ‘Van’ cherry varieties. Its popularity is due to its delicate flavor profile, often having a higher Brix sugar rating than its parents. For those considering planting this tree, its final size depends on its inherent genetics, the rootstock it is grafted onto, and ongoing management through pruning.
Standard and Dwarf Dimensions
Rainier cherry trees are generally available in two main size categories, which determine their potential mature height and spread. The standard form is a vigorous grower, capable of reaching significant proportions. A mature standard Rainier cherry tree can reach heights between 25 and 35 feet, with a corresponding spread of 20 to 30 feet.
The dwarf or compact forms are much more manageable for small yards or high-density planting systems. Dwarf trees typically mature to a height of 8 to 15 feet and maintain a spread of 8 to 12 feet, making them easier for harvesting and routine maintenance. The smaller semi-dwarf category often falls in the middle, generally reaching 12 to 15 feet tall. These size differences are primarily determined by the underground structure supporting the tree.
The Role of Rootstock in Determining Size
The ultimate size potential of a Rainier cherry tree is genetically pre-determined by the rootstock onto which the ‘Rainier’ scion is grafted. Grafting is a horticultural technique where a piece of the desired fruit variety (the scion) is fused to the root system of a different plant (the rootstock). This process is performed because the rootstock controls the vigor, or growth rate, of the entire tree.
Standard-sized trees are often grafted onto a vigorous rootstock like ‘Mazzard,’ a wild sweet cherry seedling that allows the tree to reach its full genetic potential. In contrast, smaller trees use clonal rootstocks specifically bred to restrict growth, known as dwarfing rootstocks. The ‘Gisela’ series, such as Gisela 5, is a common example of this type of rootstock for sweet cherries.
A Rainier tree on Gisela 5 rootstock may only reach about half the size of one on Mazzard rootstock. These dwarfing rootstocks effectively limit the tree’s size by reducing the growth of the canopy above the graft union. This genetic control over vigor is a permanent feature, setting the biological upper limit for the tree’s final size.
Pruning Techniques for Size Management
While rootstock sets the potential for size, the actual size of a Rainier cherry tree is maintained through active pruning and training. Pruning is necessary for sweet cherries to ensure proper light penetration and air circulation, which helps manage disease and promotes healthy fruit production. The goals of size management are to keep the canopy productive and the fruit within an easy reach for harvest.
One technique for size control involves making heading cuts, which remove the terminal end of a branch or the central leader. By cutting back the main vertical growth, the gardener reduces the tree’s height and encourages outward, lateral branching. This action helps maintain the tree at a stable height, such as keeping a dwarf variety under 10 feet.
Sweet cherry trees like Rainier are typically trained to a central leader system, which maintains a single, dominant trunk with well-spaced lateral branches. This structural approach helps manage height and ensures the tree maintains wide crotch angles where branches join the trunk, which are necessary to support the weight of a heavy fruit crop. Regular pruning, especially during the dormant season and after harvest, is the practical method used to manage the tree’s dimensions throughout its life.