What we now call the sweet cherry (P. avium) has been around for a long time and predates what we now call the tart cherry (P. cerasus). Sweet cherry is, in fact, thought to be one of the parent species of tart cherry, the other parent being Prunus fruiticosa (European dwarf cherry). With considerable difficulty, all three species can breed with each other. Though historically related, the sweet and tart cherries have different numbers of chromosomes. They also differ significantly in tree size, pollination, winter hardiness and disease and insect susceptibility. Sweet cherry is a more “needy” species in terms if its environmental requirements and adaptability. One result is that there have been many more selections made to help address specific requirements, but lack of genetic variability still limits where sweet cherries can be grown with commercial success.
Sweet cherries have a shorter chilling requirement than tart cherries, making them more susceptible to over-wintering fruit bud damage. They also bloom earlier, making them more susceptible to crop loss due to late spring freezes. Most are not self-fertile and have specific cross-pollination requirements. They are also more susceptible to insect and disease damage as well as environmental conditions, such as rainfall during ripening, that cracks and spoils fruit. Despite these shortcomings, sweet cherries are an economically profitable crop when site conditions are favorable.
Sweet cherries are less cold hardy than tart cherries by at least 15-20 degrees F, but it is usually the shorter chilling requirement that is the most limiting factor for site selection. In northern areas it is important to find a meso-climate that moderates late winter and spring temperature extremes. Areas near (and especially downwind from) large bodies of water that do not freeze over provide a good environment for the sweet cherry and other commercial fruit crops with low chilling requirements (such as peaches and apricots).
Observations at Carandale Farm
The inland climate at Carandale Farm is not favorable for the commercial production of sweet cherry, but limited success had been achieved with a prior experiment. An 8-10 percent slope, a northern exposure and a 50-foot drop in elevation provided enough meso-climate effect to minimize fruit bud mortality and late-spring freeze damage. One tree each, of two cultivars (one yellow fruiting and one red fruiting) was planted on the site in the mid 1970s. The trees are still fruitful after nearly 40 years. The resident bird population now harvests these large trees annually. When the trees were smaller, there were a few good harvests before birds completely took over. It took the birds a few years longer to add the yellow cherries to their diet.
Dormant White Gold sweet cherry tree
Based on this experience, and with the introduction of new cultivars (from the New York Experimental Station) reported to be more winter hardy and crack and disease resistant, Carandale decided to include sweet cherry in the test plot. Cultivars selected for observation were planted in 2003. All have adapted well and are healthy, vigorous trees as shown in the photographs.
‘White Gold’ (PPAF, NY13688 cultivar ‘New Fane’) is a red and yellow, mid-season cherry said to be “good size, good flavor, a consistent heavy cropper, resistant to cracking and to bacterial canker.” Two trees grafted on the very dwarfing ‘Giessen 148-2’ (also called ‘Gisela 5’) rootstock were established in the test plot. ‘White Gold’ is self-fertile.
Black Gold sweet cherry tree in bloom
‘Black Gold’ (PRAF, NY13791 cultivar ‘Ridgewood’) is “a deep red (almost black) disease-resistant sweet cherry that is late blooming and self-fertile, so it sets a big crop where others fail.” It is large, firm and very flavorful. Its dark pigmentation indicates that it could have high anthocyanin content (Marini, 2009) . Two trees grafted on ‘Giessen 148-2’ rootstock are included in the test plot.
‘Kristen’ is one of the more winter hardy of all standard sweet cherry cultivars. It was planted for hardiness comparison with ‘White Gold’ and ‘Black Gold’. Two trees are on the ‘Giessen 148-2’ rootstock for direct comparison. There are also two trees on ‘GM-61’ rootstock. This was done to evaluate differences in hardiness, precociousness, tree size and vigor based on different rootstock choices with the same scion (cultivar).
Kristen sweet cherry tree in bloom
‘Kristen’ is a good cultivar in its own right. It is crack and bacterial resistant. “The large black fruit is firm with a red flesh that is aromatic and has a sweet flavor.” It is said to be winter hardy to -25 degrees F (Zone 4), but is not self-fertile.
All cultivars established well, but one of the ‘Black Gold’ trees died several years after planting, probably from bacterial canker. The remaining trees show no sign of disease, except for some leaf spot. Photos show that ‘Black Gold’ is later blooming, but it has not made an observable difference in fruit set. Fruit set has been poor on all three cultivars, probably due to the 3 percent slope, eastern exposure and 10-foot drop in elevation does not provide sufficient contribution to meso-climatic protection for fruit buds during eco-dormancy. Bloom will also be more affected from late-spring freeze events at this site v. the preliminary test site. Had it not been for unusually warm weather in March, 2012 could have been a good crop year. Unfortunately, the weather forced everything into early bloom that froze in April.
Observations confirm that sweet cherry fruit is quite susceptible to brown rot in a humid environment. This species will require an environment that extends endo-dormancy and protects it from temperature extremes during eco-dormancy. This is primarily an issue of site selection, whereas protection from late-spring freezes can be achieved by other methods.