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Rootstocks
At present no known adaptable peach rootstocks induce dwarfing in peaches. Peach seedlings are still the principal rootstock source for commercial peach trees. Seedlings can be divided into three classes: wild types (e.g., Tennessee Natural), commercial cultivars (Halford and Lovell), and seedlings developed for use as rootstocks (Siberian C, Bailey, Rutgers Red Leaf). Interspecific hybrids are also being evaluated in Pennsylvania. They have been developed from crosses between peaches and almond (Nemaguard, GF 677). Finally, nurseries are exploring the possibility of rooting peach cuttings without propagating them on a rootstock. Following are comments about specific rootstocks that are currently available or that might have potential:
Halford: Grown in California as a canning clingstone type. Some nurseries obtain seed from this open-pollinated fruit, while others have seed blocks and collect fruit only from self-pollinated trees. Seedlings from self-pollinated fruit usually produce the most uniform trees. Halford is compatible with all commercial cultivars.
Lovell: Also grown in California as a clingstone for dried fruit. Seeds are obtained from self-pollinated blocks and perform like Halford.
Bailey: Developed in Iowa for its cold hardiness. Preliminary trials indicate it to be as productive as Halford and Lovell; however, only a few nurseries offer trees on this rootstock for sale. Only small trial plantings are recommended.
Citation: A peach-apricot-plum hybrid developed in California by Floyd Zaiger. Reportedly tolerant to wet soils, it is compatible with plum and apricot and provides 50 percent dwarfing. However, it cannot be recommended yet because not enough is known about its performance in Pennsylvania. Preliminary studies indicate that it may not be compatible with Redhaven.
Other newer rootstocks are being tested across the country as well as in Pennsylvania. Most originated in Europe and are interspecific hybrids. The main criteria for their development were a tolerance to wetter soils and tree longevity. St. Julian is compatible with peaches and plums and supposedly reduces scion vigor by 10 to 15 percent. Damas (GF 1869) is a plum hybrid compatible with peaches and plums but not nectarines. A serious drawback observed in Pennsylvania is the large output of root suckers from this stock. Amandier (GF 677) is a vigorous rootstock fully compatible with peaches, plums, and nectarines.
Many California nurseries have recently been selling several new rootstocks. Krymsk 1 (VVA-1) and Krymsk 2 (VSA-1) were developed in Russia along the Black Sea for their dwarfing ability and cold-hardiness. Both are compatible with peach and plum. Hiawatha is another rootstock that is available commercially. It provides about 10 percent dwarfing capabilities. They have not been tested in replicated trials in the Mid-Atlantic region.
The University of California at Davis is also in the process of releasing two size-controlling rootstocks for peaches and nectarines. Controller 5, tested as K-146-43, reportedly produces a tree about 50 to 60 percent of the size of trees on Lovell. Controller 9, tested as P-30-135, reportedly produces a tree about 90 percent of the size of trees on Lovell. A study comparing these two rootstocks and others can be viewed online in the California Agriculture Journal at http://calag.ucop.edu/0502AMJ/pdfs/Rootstocks.pdf.
A final option becoming more common is to grow peach trees on their own roots. These trees do not have a true rootstock, but only the scion cultivar. They are expected to be more uniform than those grafted onto a rootstock. Their ultimate size varies according to the genetic makeup of the scion cultivar. Very limited information is available about how these trees perform in Pennsylvania. Indications are, however, that self-rooted trees may be more drought tolerant and able to absorb nutrients more efficiently.
The following peach rootstocks, which may be available from certain nurseries, are not recommended for use in Pennsylvania for the reasons listed. Siberian C does not survive well in areas with fluctuating winter temperatures. Nemaguard has been found not to be cold hardy in this region. P. tomentosa and P. besseyi lack vigor and have compatibility problems.