Many factors need to be taken into account when choosing rootstocks for a new cherry orchard. Soil fertility, variety, and training system are some of the more important ones.
In most cases, you will want to avoid the most dwarfing rootstocks, such as Gisela 5 and Krymsk 6, where soils are shallow or low in fertility. Other productive rootstocks such as Gisela 6, Krymsk 5, or even Maxma 14 may perform more satisfactorily on these sites, but higher planting densities should be considered where soils are poorest.
Other soil/ rootstock combinations to avoid include planting Mahaleb rootstocks in heavy soils. Mahaleb will do poorly under these conditions, and will potentially die out, whereas Krymsk 5 and 6, although not adapted to wet soils, will survive in heavier soil conditions than Mahaleb or even Mazzard.
At the most dwarfing end of the spectrum is Gisela 5, which is the only commercially available rootstock in the United States that reduces vigor by 50 percent or more. As such, it is best positioned for very high density plantings of 450 to 550 trees per acre. For the most part, Pacific Northwest growers have moved away from Gisela 5 due to the relatively low vigor of this rootstock. Many Europeans, however, believe that Gisela 5 is too vigorous and are exploring the potential for even more dwarfing rootstocks such as Gisela 3. There is some evidence that some of the early Gisela 5 plantings failed because trees were planted too far apart. Super high density plantings encourage heavy pruning which increases the potential for success of rootstocks such as Gisela 5.
Due to its low vigor, Gisela 5 is probably best suited for spindle systems such as the Vogel central leader or the upright fruiting offshoots (UFO) system developed by Dr. Matthew Whiting of Washington State University. In addition, it is best to avoid very precocious varieties such as Sweetheart and Lapins in combination with this rootstock as they too easily overset and inhibit growth.
On the other end of the size spectrum are rootstocks like Mazzard, Colt, and Mahaleb that are best suited for standard density orchards of 120 to 160 trees per acre. However, when trained as a Spanish Bush or modified Spanish Bush (Kym Green Bush), all three of these rootstocks have been grown at densities of 300 to 340 trees per acre in the Northwest, as well as places such as Australia and Spain.
Due to the strength of these rootstocks, a spindle or central leader system is usually not recommended for these standard rootstocks since these trees would tend to grow very tall. In addition, varieties of low productivity, such as Regina and Tieton, have not provided satisfactory yields on these rootstocks.
In the middle are the majority of the precocious rootstocks such as Gisela 6 and 12, Krymsk 5 and 6, and Maxma 14. Moderately deep to deep soils are normally recommended for these rootstocks, with the recognition that higher density plantings are needed for poorer soils. These rootstocks are well suited for all of the more modern training systems grown in the Northwest, with the possible exception of Maxma 14 combined with the upright fruiting offshoots system, due to the vigor of that rootstock. Typical planting densities range from 445 trees per acre with the UFO system to 242 trees per acre on an 18 feet by 10 feet steep leader planting.
As with soils and planting systems, these moderately vigorous rootstocks are also more widely adapted to and grow well with most variety combinations. It is true that the most productive varieties such as Sweetheart and Lapins can be a challenge with any size-controlling rootstock, but even with these combinations, growers have been successful at consistently growing high quality fruit. The key is to pay close attention to pruning principles and to perform required procedures in a timely fashion. While productive varieties can be challenging, these moderately size-controlling rootstocks are just right for varieties of lower productivity such as Regina and Tieton, and perform well with moderately productive varieties such as Bing, Skeena, and Benton.