Tuesday, June 3, 2014

Forcing a bark graft

   Five weeks ago I top-worked a Jayhawk tree over to a new cultivar by placing a bark graft on the tree's central leader. Today, I returned to this tree for a little post-grafting maintenance. After some much needed rain fell over the weekend, the tree was exploding with rapid shoot growth including multiple shoots growing from the scion (photo above).  I like to prune newly grafted trees frequently during the first summer of grow and the first of June was a great time to get started.

    My first step was to remove all trunk sprouts growing on the central stem below the graft union. I also removed any new shoots that had sprouted from lower lateral limbs that were growing in direct competition with the central leader. Before and after pruning photos are shown above.

    My next step was to choose a single shoot growing from the scion and train that shoot to a bamboo stake. In the photo series above, you can see that the scion sprouted three, equally-vigorous shoots. I pruned out the lower two shoots and kept the shoot growing from the top of the scion. I made this choice based on the direction this upper shoot was growing--right in line with my bamboo stake. I then used some flagging tape to tie the remaining shoot to the stake to prevent wind damage to the tender shoot.

    Next, I moved to pruning the rest of the tree. All the cuts I make on lateral branches below the graft are aimed at reducing competition with the central leader, slowing the growth of lateral limbs, and directing more of the tree's energy towards the scion. My first step was to inspect the tree and remove any limbs that tended to grow upward.
    The red arrow in the photo above points to an upward growing limb. I removed this limb by pruning back to the point it connected to a major lateral limb. The photo above-right shows the tree after pruning.

    I then walked around the entire tree making directive pruning cuts on the tree's new grow.  Whenever a pecan tree starts growth in the spring, a cluster of buds breaks near the terminal of last year's shoot.  From this cluster of new shoots I leave the one shoot that is growing outward, away from the graft union. I prune out all other new shoots (photo at right). I then pinch out the terminal of the one shoot that remains in order to slow its growth.
    The photo below shows my tree after pruning and training. You should note that the new graft is fully exposed to sunlight and remains in the central leader position. I'll need to revisit this tree in a few weeks to prune where necessary and to keep the rapidly growing graft tied to the stake.