Wednesday, April 26, 2017

Tips for grafting pecans with the 3-flap graft

   The weather the past several days has been great for grafting pecan trees. There is nothing better that spending time outdoors carving scions and placing grafts. In a previous post, I've documented how I make a 3-flap graft but this year I took some photographs that I hope will shed additional insights into using this grafting technique.

    I use the 3-flap grafting technique exclusively on small pecan trees. The tree pictured above (on left) had a single stem and was about four feet in height. To encourage the tree to accept my graft, I cut the stock tree down to about 1/3 of its original height (above, right). Whenever I'm grafting, I always remove a significant portion of the stock tree's top growth to encourage the tree to accept the scion.
    In the photo above, I'm holding the top portion of the stock tree I removed before grafting. As you can see, new shoots were emerging from tree indicating the the bark will slip and the time was right for grafting. In addition, my finger is pointing to the annual growth ring on this tree that marks the spot where growth started the previous growing season. The tree put on two feet of new top growth last year which indicates, to me, that the stock tree is ready for grafting and will force the scion to grow vigorously this summer.
     In choosing a scion for a 3-flap graft, I try to match the diameters of scion and stock as closely as possible (photo at right). If I can't find a perfect match, I find it best to use a scion that is slightly larger than the stock (no more that 1/8 inch bigger).

  One step in the grafting process that is easy to forget is trimming the bottom of the scion back to fresh green wood. In the photo at right (top photo), you can see what the bottom end of the scion looks like when taken out of the cooler. I always make sure to clip off about a quarter inch of wood off the end of the scion to reveal fresh, green wood (lower photo at right) . Remember, only living cambium tissue on the scion will unite with cambium tissue on the stock.
    When it comes time to carve the scion, folks always ask me how long to make the peeling cuts. My answer has always been to let the dimensions on my hand determine the cut length. To start the cut, I always place my thumb on the bottom  of the scion. Then, holding the knife firmly in my fingers, I stretch my hand outwards and place the knife blade on the scion (photo at right). I start the peeling cut at this point and remembering to move my thumb off the scion as I cut downwards. In all my of years of grafting, my hand has always been the same size and, as a consequence, all the cuts I make on the scion will be exactly the same length.
    In carving the scion for a 3-flap graft, it is very important to cut deep enough to see white wood in the center of each cut surface. In making the three cuts,  it is also important to make those cuts equidistant around the scion (photo at left). A properly cut scion should have 3 sides cut down to the wood with a strip of bark between each cut surface. Carving the scion correctly is critical for grafting success.  Most 3-flap graft failures can be traced back to not cutting deep enough to expose cambium or cutting off all the bark thus removing all the scion's cambial tissue.
    Inserting the scion into the stock and securing the flaps over the scion often causes frustration among novice grafters. I've discovered an easy way to complete this step without the help of a third hand. Before inserting the scion, I start wrapping grafting tape around the stock tree starting just below the base of the flaps. As I wrap upwards, the flaps are pulled together forming a tube of bark. At this point, I can hold the tape in place and use my other hand to insert the scion. The bark tube will seem a little small for the scion but that's good. Once I push the scion all the way down to meet the wood of the stock, the bark tube will hold the scion in place (as long as I keep holding the grafting tape tightly). At this point, I can continue wrapping the graft union without having to hold onto the scion. The graft wrapping process is pictured above.

   After wrapping the graft with tape, I cover the graft union with aluminum foil and a plastic bag. The next step I take is to prevent wildlife damage to the graft. In the past, I always attached a bird perch to the graft to prevent scion breakage by birds. However, deer have become such a big problem in my area that I am now placing a cage over each young tree and new graft (photo at right). Left unprotected, browsing deer will eat shoots emerging from a new graft and usually break off the scion in the process. The deer cage has the addition benefit of protecting the tree from perching bird damage (birds prefer to perch on the cage instead).  As you can see in the photo, I'm still attaching a bamboo stake to the tree to serve as a training guide once the scion starts to grow.

    As I was grafting trees, I noticed a small unprotected pecan seedling that had been chomped by a passing deer (photo at left). Deer simply love the taste of emerging pecan shoots. This tree will recover and grow more leaves this summer but I will also need protect the tree with a deer cage to make sure this seedling grows strong enough to accept a graft in future years.

Wednesday, April 19, 2017

Choosing where to graft a pecan tree.

    Most of my pecan trees have budded out about a week ahead of their average date of spring leaf burst. So this evening I gathered all my grafting supplies, a box full of scions, and headed for the field to apply my first grafts of the 2017 growing season.
    The first tree I came to was a little over six feet in height with a top divided into three main branches (photo at right). For some, this tree would provide the prefect opportunity to place a 3-flap on each of the branches in an effort to increase the likelihood of obtaining at least one good graft. However, grafting close to the top of a tree actually increases the probability the tree will reject the grafts and simply grow around the scions.
   When grafting trees of this size, I cut the tree off leaving the main trunk about two feet tall (photo at left). You might cringe at the thought of cutting the tree back so far, but I look at it as forcing the tree put all its root energy into the scion that I will place on the stock tree. In addition, I often choose to graft to trees at this height so I can sit on my cooler and graft comfortably. I can certainly graft more trees in a day if I'm comfortable when carving scions.
    I used a bark graft to attach the scion to stock (photo at right). As my usual custom, I then attached a bamboo stake to the tree to protect the scion from bird damage and provide a place to tie up the scion's new shoots to prevent wind damage.
   Because I removed so much of the top of the stock tree, this scion will grow with a lot of vigor. I'll trim the scion down to a single shoot about 4-6 weeks after grafting. The combination of vigorous growth and a single shoot will make training this new tree to a central leader shape very easy.
    The final step in grafting this tree was to place a deer cage around the tree (photo at left). The local deer herd loves the taste of emerging pecan leaves and I definitely don't want all my grafting efforts to be destroyed with a single bite.

Tuesday, April 11, 2017

Pecan trees breaking bud

From L to R: Hark, Major, Giles, Faith (11 Apr 2017)
    Over the past week, our pecan trees have started their spring flush of new growth. At this early stage of bud growth, differences among pecan cultivars are clearly evident. The photo above shows four protandrous cultivars with bud development that ranges from bud swell (Hark) to an early phase of leaf burst (Faith). This arrangement of twigs also reveals that the catkins of protandrous cultivars seem to burst out of their buds before leaves start to unfurl.
    In contrast, the photo below shows 5 protogynous cultivars with a range in bud stage. The buds on the Goosepond twig are just barely getting started while the Lakota twig has leaves unfurling. Once again the flowering habit of these cultivars is clearly displayed. At this point, catkins of protogynous cultivars are still hidden inside their buds and won't start to emerge for several weeks.   

From L to R:Goosepond, Colby, Kanza, Surecrop, Lakota (11 Apr 2017)

Protandrous Faith vs protogynous Lakota
    The photo at right, illustrates the clear difference between protandrous (early pollen shedding) and protogynous (late pollen shedding) cultivars. If you every want to discover the flowering habit of a seedling pecan tree, this early stage of bud break is the best time to make a positive determination.

Monday, April 10, 2017

Pecan bud break influenced by soil type

    The buds of my Kanza trees are beginning to show some life. However, I've noticed some differences in the timing of bud break among my trees. The photo at right shows two Kanza twigs collected on the same day (10 April 2017) and growing only 500 yards apart. The only difference between these two trees is the soil that supports their growth.
    The twig of the left comes from a tree growing in an Osage silty clay. In contrast, the twig on the right is from a Kanza tree growing in a Cherokee silt loam. Both soils originated as river deposited sediments. The Osage soil is a true river bottom "gumbo" soil while the Cherokee soil is a lighter textured second bottom soil.
    The greater the clay content of a soil, the slower that soil warms in the spring. Cold soil inhibits the growth of new roots and with slower root activity bud break is delayed.

Tuesday, April 4, 2017

Cleaning up a bark graft

   Whenever I graft a tree, I usually return to the new graft every 3-4 weeks throughout the summer to prune off trunk sprouts and root suckers. I also like to start training the new scion to grow a strong central leader. The photo at right is an example of a successful bark graft that I made last year but totally overlooked the all summer training. You'll even note that the graft union is still wrapped in aluminum foil and plastic. To get this tree back into shape, I needed a chainsaw, pruning saw, and hand shears.  
   The first step in cleaning up the this young grafted tree was to cut off all the root suckers with a chainsaw and use the hand pruning saw to remove the trunk sprouts. With just these few cuts I've already reclaiming my grafted tree (photo at left). 

    When I grafted this tree last year, I placed a single scion under the bark of the stock tree. At that time, the stock was about 3 inches in diameter  (photo at right, grafting knife set on trunk for scale). Once the graft took, the scion grew vigorously sprouting numerous new shoots. Unfortunately, none of the shoots from scion produced a strongly dominate central leader. This  scion needed pruning desperately to carve out a single tree trunk.

    In pruning the scion, my first step was to trim the stock at an angle to encourage rapid wound closure. To make the cut, I used a small chainsaw to cut the stock tree at a angle of between 30 and 45 degrees (photos above). Not only does this angled cut enhance  healing,  it also encourages water to run off the wound, promoting rapid wood drying and helping to inhibit wood rot.

  Next, I used my pruning saw and clippers to prune the scion into a single shoot (photo at left). Later this summer, I'll need to train this one remaining stem to grow into a strong central leader tree. By removing all of  root suckers, stump sprouts, and more than one half of the scion's shoot growth, this tree will have a lot of pent up energy to sprout new growth come this spring. I will definitely need to revisit this tree with my pruning shears on a regular basis (every 3 weeks) to direct all new growth in the right directions. I'm positive that new trunk sprouts and root suckers will try to grow this summer. But this time,  I'll be quick to prune them as soon as they develop.

   The photo above gives you an idea of what the tree looked like before pruning and then after I had carved out a central leader. At this point it looks like I've pruned the tree into a telephone pole. However, I assure you, that with proper directive pruning, lateral branches will form and the tree will begin to fill out.