A different mindset is needed when pruning sweet cherry trees on Gisela rootstocks than on Mazzard, says Lynn Long, Oregon State University Extension educator. Gisela rootstocks are precocious and productive and require growers to prune to reduce the crop load, whereas with Mazzard, growers are trying to encourage precocity and productivity.
Long has developed pruning guidelines for Gisela rootstocks, dividing the process into four easy steps:
1 Remove pendant and small wood. Get rid of the weak wood that won’t have enough leaves to support a crop. “Small wood is bad news on Mazzard trees, but disaster on Gisela.”
2 Remove one-third to one-half of last year’s growth. During the dormant season, tip all branches. This will reduce the future crop but increase fruit size. He also suggests growers consider tipping of Lapins and Sweetheart when grown on Mazzard.
3 Do renewal pruning, stubbing back 20 percent of all fruiting wood. During the dormant season, leave 5- to 20-inch–long stubs. Stubbing will reduce the current season’s crop and renew spurs for the following year.
4 Thin shoots at top of tree to a single branch. This should be done during the dormant season, and the tree should be left in a pyramid shape to allow light penetration throughout.
The pruning steps were published in an Oregon State University Extension bulletin and can be downloaded free at extension.oregonstate.edu/catalog/pdf/pnw/ pnw592.pdf.