Monday, February 29, 2016

Unequally yoked: grafting hickory on pecan and pecan on hickory.

    Pecan and hickory are closely related, both belonging to the genus, Carya.  Pecan and hickory are also graft compatible meaning scions from one species can be grafted successfully on a tree from another member of the Carya genus. The question becomes, should these type inter-specific grafts be made?
    Pecan is the fastest and largest growing species in the hickory family. Because of this fact, I often recommend that hickory nut enthusiasts graft their favorite hickory cultivars onto pecan roots. The vigor of the pecan rootstock pushes the hickory scion to grow faster and to start producing nuts earlier.
    The photo at right shows two hickory cultivars (smooth bark) grafted on to a single forked pecan tree. Note how the pecan portion of each graft union has already grown larger in diameter than the hickory tops.
    One word of caution. If this were my tree, I would have pruned out the fork in this tree long ago and kept just a single hickory cultivar.  As this tree grows larger, the chances of this tree breaking out in a wind storm only increases.

      I do not recommend grafting pecan onto hickory rootstock. Slow growing hickory will actually slow down the growth of a pecan scion and inhibit nut production. The photo at left shows what happens when a pecan scion is placed on a hickory root.  Once again the pecan portion of the tree out-grows the hickory portion. The tree becomes top heavy and the hickory roots have a hard time providing enough water and nutrients for the massive pecan top.
   It is tempting to graft pecan on to hickory seedlings because several species of hickory can tolerate drought-prone soils found on upland sites (as in the photo). Pecan, being a flood plain species, would struggle if planted directly in upland soil conditions. Unfortunately, grafting pecan onto hickory tree seedlings, already established on a upland site, will not make nut production from the pecan top any easier. The hickory root and the upland soil will never be able to provide the water needed by pecan scion to grow and fill out a nut crop.