Roots and Fruits

For years, fruit trees have grown vigorously despite soil disease and poor drainage, and the massive blossoms on this tree signal another bountiful crop (figure A). The secret to these fruit trees may be underground. These trees are growing on roots that are specifically designed for the challenges of their region. According to fruit tree expert Ed Laivo, rootstocks are for soil adaptation and disease resistance.

Different varieties of fruit trees require different rootstocks. So how do you know which rootstocks you need? Your local nursery generally does the research for you in selecting the most adaptable varieties for your region. In California's central valley, a versatile rootstock for the region is Citation (figure D).

This is the stock orchard for Citation rootstock (figure E). "From these trees, we take cuttings that'll be stuck in the ground and used to bud plums, apricots, peaches, and nectarines," says Laivo. This field has been planted with Citation cuttings of a peach-plum hybrid that has great roots for clay soil, but would taste terrible if allowed to fruit (figure F). But by using a method called budding, the peach-plum becomes an apricot. Workers slice a piece of the cambium layer (figure G), the layer of actively growing cells beneath the bark, and replace it with a bud from an apricot stem. Now it will grow into an apricot tree.

Nurseries also use a similar technique called grafting. Here, the rootstock is cut at a 45-degree angle (figure H). The whip, or in this case, the stem from a walnut tree, gets the same cut (figure I). A notch cut through the center of both pieces secures the two sections together (figure J). Again, the cambium layers are lined up and sealed in place (figure K). The bud will grow and develop the tree from this section (figure L).

"Genetic dwarfs are not grown on dwarfing rootstock; they're on standard rootstock, and that's primarily to encourage the vigor of the tree," says Laivo. Since genetic dwarfs grow very slow on their own roots, they need the vigor of a good standard rootstock to promote the size they need to get. He recommends liberal pruning to control the tree's size and letting the rootstock do its thing in the soil. But the rootstock won't always be the way you need it to be to accommodate the plant. Planting in a raised bed, however, will give rootstocks an even greater advantage against harsh, native soil.

"When you go to the nursery to select a tree, always take with you a clear example of what your soil conditions are like," says Laivo. Test your soil's drainage too. Ask questions about primary disease problems that may exist in your area and whether or not there are rootstocks in your area that may be able to help you avoid this problem.

"Selecting the right rootstock can make growing fruit trees at home a sweet, successful and satisfying experience," says James. If you have a young fruit tree at home that's not doing well, it could be the rootstock. Laivo estimates that half of all trees that die before the five-year mark most likely had the wrong rootstock and simply couldn't adapt to the soil conditions. So before you plant, make sure you have the right rootstock.