One of my favorite childhood memories is of picking ripe, juicy nectarines from my parent's backyard trees. They were homely little fruits, but they were sweet and mellow, and they melted in my mouth. Last summer, my own children harvested nectarines from that tree in our backyard. How can that be? The fruits came from grafted fruit trees.
What is grafting? Insert a small twig cut from one fruit tree into a cut in another, compatible fruit tree. If you've placed the grafts correctly, the twig will soon start to grow on the host tree and eventually produce fruit. Of course, this is a simplified description, so let's review the process in greater detail.
You probably assume (correctly) that you can graft any two peach varieties with each other, as well as any two apples, cherries, figs, plums, nectarines, and so on. Nearly all citruses are compatible with all other citruses. Also (and this is where the fun starts) most fruit trees in the Prunus genus are sometimes compatible with each other: almonds, apricots, nectarines, peaches, and plums all are compatible for grafting, but occasionally it's complicated. For example, some plum rootstock is not compatible with peaches or nectarines; and some almonds require an intermediate step before grafting onto some plum rootstocks.
After consulting experienced grafters, reading catalogs, and surfing the Internet, my husband and I chose a combination of varieties that aren't typically found in supermarkets and that ripen over the growing season rather than all at once for our garden. We also wanted varieties that would pollinate trees that we already had in our garden.
The key to grafting success is matching the cambium layer of the scion wood to the cambium layer of the rootstock. The cambium is a narrow band of cells just inside the bark. The cambium makes the xylem cells that carry water up from the roots and the phloem cells that carry the sugars of photosynthesis down from the leaves. For a good union, the cambium of the scion must line up as closely as possible with the cambium of the rootstock, thus ensuring the transfer of nutrients and water.
There are many different grafting and budding styles and techniques -- T-budding and chip-budding, whip-and-tongue grafts, and cleft grafts, among others. Because different types of grafts seem to work best on particular species, talk to experienced grafters and do some reading before you pick a method to try on your trees.
The best way to learn grafting is from an expert. Our grafting mentors are Jim and Lee Bathgate, San Diego area members of California Rare Fruit Growers. Jim and Lee farm five acres of unusual varieties of apricots, nectarines, oranges, peaches, and 'Fuyu' persimmons in Valley Center, California. Over several months, they gave us a course in grafting.
We started collecting scion wood -- new, vigorous growth trimmed from desirable trees -- in late winter for early spring grafting. Though early spring is the best time to graft deciduous fruit trees like apples and stone fruits, tropical fruit trees like avocado and citrus can be grafted later in the year. The best scion wood is no more than one year old and 1/4-to 1/2-inch in diameter. We were careful to avoid wood from diseased trees.
Most of our scion wood came from an exchange sponsored by the local chapter of California Rare Fruit Growers, but scion wood exchanges take place around the country -- even among neighbors. (Our scion wood included prunings from my parents' nectarine tree.)
If you collect your own scion wood, cut it into 12-inch lengths, and be sure to keep track of the "top" or growing end, and "bottom" or root end of the scions. Experienced grafters showed us how to mark the top with a diagonal cut and the bottom with a square cut. Then label each length with the variety name. We bundled our scions and labeled each bundle with masking tape and waterproof markers. Next, we wadded damp (not wet) paper towels around the cut ends of the scions, and placed them in large plastic bags. Finally, we sealed each bag with rubber bands and put the bags in the refrigerator. Our goal was to keep the wood moist and cool to maintain its dormancy until we were ready to graft. Scion wood can keep like this for up to six months in the refrigerator, as long as it doesn't freeze.
No matter where you live, collect scion wood from deciduous trees before the buds start to grow. Cut scions when temperatures are at or above freezing, between 10 a.m. and 2 p.m., when the sun is up and causes the sap to flow. If you live in a frost-free region of the country, you can graft at any time before new bud growth begins.
After we grafted our trees, we waited, impatiently, for three or four weeks. Then one day, we noticed that the first graft had developed tiny green buds. Over the next few weeks, more than 30 of our 40 grafts developed buds. Within two months of grafting, all the successful grafts had started, though four or five that had appeared to take later withered. The withered grafts had sprouted using only their own energy, rather than forming a true union (called a callus) with the rootstock. Soon, however, we had substantial new growth from about two-thirds of our grafts. If you decide to try grafting, use at least 10 scions of each variety to ensure that some will take.
When we grafted, we covered our grafts with small paper bags to protect them from excessive sunlight. We checked them frequently to remove earwigs, sowbugs, and other critters that could eat new growth. We also pruned branches of the mother tree back by about 65 percent so that the tree would direct food energy into the newly grafted branches. We pinched flower buds from the new grafts to encourage strong, healthy branches rather than fruit the first spring. After that, we allowed the previous year's grafts to flower and fruit while we grafted even more varieties. Because some varieties grow more vigorously than others, long-term care includes additional careful pruning so that one or two varieties don't dominate a single tree.
If you have the patience and a sense of adventure, why not give grafting a try in the garden this year.
Photo courtesy of the USDA.
Article published on June 23, 2008.