Human families often include members of diverse cultures, and some human communities are described as melting pots. Botanical families are less flexible. Hybridizing between different members is restricted to subfamilies or genera. Varieties within a genus abound, but crossing the genus line awaits future botanical innovation. A hybrid of weeping cherry and crabapple trees is not possible at present, even though both are members of the large Rosaceae family. Both cherries and crabapples come in weeping varieties.
How Trees are Hybridized
Tree hybridizing is a mechanical process that still depends on its centuries-old methodological roots. One by one, portions of one tree variety are grafted onto another variety by hand. This involves attaching a branch of one variety to the trunk of another, wedging a bud of one variety into the rooting crown of another or cutting the top of one tree and binding it to the trunk of another. An heirloom apple with extremely good flavor might be strengthened against winter damage by grafting it to the rootstock of a hardier variety. Heavier fruit or flower production, disease resistance and hardiness are all reasons to resort to modern versions of this ancient process of hybridizing, or cross-breeding, expressed in the varietal name by the simple letter "x."
The Physiology of Hybridizing
Just as human transplants depend upon tissue and blood-type compatibility, tree hybrids depend upon the abilities of tissues to work with each other. Critical to tree success are two thin layers under the bark of the tree, cambium and phloem. These tissues transmit nutrients to the new graft and form the new living cells that make the graft part of the plant.
Prunus Hybrids and Weeping Cherries
The Prunus genus includes plums, cherries, apricots and almonds, leading to a now-familiar and tasty cross between seemingly disparate plum and apricot, called the pluot or plucot. Among ornamental cherry trees, several varieties are bred for a weeping growth habit. Best known in the U.S. is the Higan weeping cherry, which can reach heights of 25 to 30 feet. Dwarf weeping varieties include P. Snozofan, white, and P. Kiku Shidare Zakura, or Cheals, pink double. Zakura, also spelled Sakura in Japanese materials for English speakers, is the variety of weeping cherry at the heart of cherry blossom viewing festivals and parties all across Japan.
Malus Hybrids and Weeping Crabapple Trees
A 1999 University of Florida Extension list of crabapple varieties available in U.S. nurseries more than supports its assertion that there are hundreds of crabapple hybrids or cultivars. The span of blossom colors is broader than it is for cherries with white, pink, reddish and even purplish blooms are available. Tree forms include erect, oval, fountain shaped and weeping. Crabapples generally grow between 10 and 20 feet tall. Among weeping varieties are Red Jade, Oekonomierath Echtermayer and Weeping Candy Apple.
Until Hybrids Appear
Whether a cherry-crab hybrid ever becomes viable, available choices of both varieties make it possible for you to add a weeping tree form to your landscaping. If the weeping form is your primary consideration, you may wish to look beyond just cherry or crabapple trees. Consult a County Extension list of flowering ornamental trees for your area, like the one available through Clemson University for Southern states. If cherry or crabapple is a must have, look at other shapes broadening your choices. A multistem or spreading variety may create the overall look you want without tying you to a small group of officially weeping varieties.