Friday, May 27, 2016

Forcing scion growth on new grafts

    Its been a month since I started grafting pecan (and hickory) trees.  So far, it looks like I have a perfect success rate with many grafts already pushing out new shoots (photo at right).  One of the most overlooked keys to preserving graft success is taking the time to come back to each grafted tree and trimming off the trunk sprouts that emerge below the graft union. So yesterday, I started inspecting each graft armed with my trusty pruning shears.

     In the photo at left, you can see that I have a successful bark graft growing on a fairly large seedling tree. Below the graft union, numerous trunk sprouts have also started to grow. Note that the leaves of these sprouts are reddish in color. Red pigmentation on new leaves is a common characteristic of a juvenile pecan tree. The sprouts growing from the scion are pure green indicating that these shoots are growing from sexually mature tissues (ready to bear nuts). To make sure the tree focuses its energy on growing scion shoots, I used my clippers to remove all trunk sprouts. I also pruned off any upward growing shoots sprouting on side limbs that I left on the tree to provide photosynthetic energy to the root system.

     A month ago, I placed a hickory scion on a small hican rootstock using and arrowhead graft (photo at right). The hickory scion has sprouted nicely but the rootstock has already sprouted extremely vigorous shoots that are growing at a rate that would soon engulf the scion.  That's the problem with not getting back to inspect grafts several times during the summer. Some trees try to grow around a scion rather than invest tree energy into growing a "foreign" shoot (the scion). The quicker you get competing trunk sprouts pruned off,  the more tree energy will be forced into the growing scion shoots and more wood with be formed to grow over the graft union.   

Tuesday, May 24, 2016

Tree training: Directive pruning helps avoid major pruning headaches

    Last month, I received my copy of "Pecan South" which featured a photo of a young tree on the cover (photo at right). One look at the photo and I couldn't help but think this tree had received zero attention since it was planted. The tree had a nice straight trunk that was topped by a cluster of branches growing in every direction. The tree had already lost its central leader.
     How can such an obviously strong growing tree lose its central leader so quickly? Yesterday, I was pruning some trees I grafted last year and I think I discovered the answer.
    The tree pictured at left was grafted last year. After making some judicious directive pruning cuts last summer, the scion grew a nice straight trunk over four feet in length. However, this spring, the tree burst forth with new shoots from every bud near the top of the tree. If I had let nature take its course, I would end up with with a tree looking very much like the one on the cover of the magazine.

    Take a closer look at the top of my young tree (photo at right). Growing from the top of last years wood are at least a dozen new shoots with no one shoot showing any dominance to make a central leader.

   An even closer look at the terminal of last year's growth reveals just how many new shoots are growing at the top of the tree. My job now is to identify one of the new shoots to become a central leader and to prune out all others.

    I choose to keep a strongly growing shoot that was growing out about 3 inches below the upper-most whorl of new shoots. With a single cut, I could remove a lot of the excessive shoot growth (photo at right).

    Next, I followed the 2-foot rule. I pruned off  all lateral branches that emerged from the central leader within two feet of the new central leader (photo at left).

     After making just these few summer pruning cuts I was left with an actively growing shoot that will become my new central leader (photo at right). Later this summer, secondary buds will break along the main stem to form well-angled lateral branches and to help fill out the tree's canopy.

   Over the years, I have learned that leaving a single tender shoot suddenly exposed to our strong Kansas winds is not a good idea. Within days, the exposed green shoot often snaps off in a strong gust of wind. So just like training the shoots growing from a new graft, I used electrical tape to attach a bamboo stake to the woody portion of the tree, then used flagging tape to tie the new leader to the stake (photo at left). Staking the new shoot helps to straighten up the new leader and will prevent both wind and bird damage.

Tuesday, May 17, 2016

Directive pruning a young pecan tree

    I was driving through my orchard when I noticed a young, grafted tree that looked more like a tree straight out of a Dr. Seuss book than a pecan tree (photo at right). As strange as this tree looks, this type of growth pattern is not that unusual for a pecan tree. During late summer of the previous year, a cluster of closely spaced buds formed at the terminal of each branch (including the central leader). This spring, these buds began growth and formed a profusion of new shoots right at the ends of each branch. Left to grow unchecked these shoots will compete for predominance and you will end up loosing your central leader.
   At this time of year, a few judicious pruning cuts will help direct the new growth of this tree and help maintain a strong central leader.

    I always start at the top of the tree and select a single new shoot to be my central leader (photos above). Before pruning you can see the top of this tree has 5 actively growing shoots. I selected one of these shoots to be the new central leader and pruned off all competitors. In fact, I removed all shoots within two feet of the apex of my new central leader. This helps preserve the dominance of the new leader.

   Next, I move down to the side shoots. Once again several buds broke at the terminal of last year's wood. For side branches, I remove any upwards growing shoots (red arrow) and retain outward growing shoots. After these outward growing shoots grow two feet of new growth, I'll tip prune the terminal bud to slow down the extension growth of these side limbs. 

    The lateral branch on the left side of the tree had two upward growing shoots that needed to be removed (red arrows). With just a couple of snips with my pruning shears, I was able direct the growth of this lateral branch outwards rather that upwards (upward growing shoots will compete with the central leader).

    Standing back away from this tree, it looks like I have a tree with a lot of blind wood (branch area not supporting new foliage). However, on close inspection, many buds along these stems were beginning to break bud (photo at right). As the growing season progresses, these new shoots will continue to grow, helping to fill out the canopy of this young tree. 

    After directive pruning, this young tree has lost the heavy profusion of leaves at all the terminals. I now have a single central leader and outward growing lateral limbs. By mid summer, this tree should develop additional lateral branches that will help fill out the tree's canopy

Monday, May 16, 2016

How long can I keep grafting?

     This year, I made my first pecan graft on Sunday April 24th. Exactly three weeks later (May 15th), I checked on one of those early grafts and found buds bursting from the scion (photo at right).
     During the past three weeks I've been grafting pecan trees almost every day. I've grafted trees at the Pecan Experiment Field, during grafting schools, and on my own farm. The weather forecast for this coming week is cloudy, wet, and cool--great grafting weather. At every break in the rain, I'll be outside grafting even more trees.
    One of the most frequent questions I receive during grafting schools is--"How long can I keep grafting?" The answer, like almost every outdoor activity, is that it depends on the weather. The grafting season ends when daytime high temperatures start to climb into the low 90's F. High heat seems to literally cook newly placed grafts to death. In the past, hot weather occurred as early as mid-May in SE Kansas. Most years, the heat will hold off until June.
    I watch the long range forecasts to see when weather experts predict the first real heat wave.  If a week of mild temperatures is forecast before the heat hits, I'll keep on grafting. If a heat wave is immenant, making additional grafts is not a good idea.

Thursday, May 12, 2016

Coppicing before re-grafting a large pecan tree

    Last year, I placed 9 bark grafts in a large tree in an effort to change a seedling tree into tree that would produce large, high-quality nuts (photo at right). Today, I spent nearly 90 minutes up in a hydraulic lift moving from graft to graft, trimming each graft union, and removing new sprouts growing on the trunk and main scaffold limbs. I can't imagine how long this task would take if I had to use a step ladder to access these graft unions.
    The hazards associated with grafting, pruning, and training a top-worked tree from the top steps of a ladder are obvious. No tree is worth broken bones and a extended recovery period. If you would like to graft a seedling tree that has grown too large for conventional grafting methods or you end up changing your mind on a previously grafted tree, consider coppicing the tree at ground level.    
   The practice of coppicing works pretty well for trees that have not grown over 10 inches in trunk diameter. Out in our pecan breeding plot, I've been removing trees that produce poor quality or scab susceptible pecans. As a result I have produced dozens of coppiced trees. The photo at left shows the current size of many trees in the breeding plot compared to a tree that was cut at ground level  a couple of years ago.

     In the two years since cutting the tree at ground level the tree has sprouted multiple stems from the stump (photo at right). The tallest sprouts have already grown to over seven feet in height. These fast growing shoots make excellent sites for bark grafting, and I can even make the graft with two feet firmly on the ground.

    Take a close look at the sprouts growing from the coppiced tree (photo at left). The sprouts are all growing from around the outside edge of the stump. These sprouts actually arise from epicormic buds buried under the bark of the stump.
    Before grafting this tree, I trimmed off all but the most vigorous sprout. Using my chain saw I cut off all competing sprouts at the same height as the stump (photo at right). The white wood in the photo reveals the location of the removed sprouts. The dark (stained) wood is the original tree stump.

    Once all competing sprouts are removed I have what looks to be the perfect tree for bark grafting (photo at left).  But be forewarned. The stump will produce additional sprouts this coming summer and I'll need to add stump-sprout removal to my list of summer pruning tasks.

     I usually recommend leaving a couple of lower limbs below a bark graft. However, this sprout had grown so rapidly that the lowest limbs were all above my preferred graft height. I figured that this tree had already survived coppicing, so a brutal cut for placing a bark graft couldn't hurt. I placed the graft at a comfortable height for both grafting and for summer training of the sprouted scion. Judging from the vigor of the stump sprout, this scion should make at least 4 to 5 feet of new growth this summer. I'll need to watch this tree carefully. Summer pruning to ensure a central leader and careful tying to a strong stake will be critical for graft success.

Wednesday, May 11, 2016

Mid-way through pecan pollination season

  The last few days of warm sunshine has really promoted the progress of pecan pollination season. Cultivars with the protandrous flowering habit (pollen early, pistillate flowers late) have released or are currently releasing pollen form fully ripe catkins. The photo at right shows Gardner catkins with many open pollen sacs that have started to turn brown in color since all the pollen has already been released.
Looking over at the terminals of the Gardner tree's new growth I found numerous clusters of pistillate flowers (photo at left).  Gardner, like all protandrous cultivars, produce pistillate flowers late in the pollination season. The stigmas of Gardner flowers turn red and glossy when receptive to pollen. The flowers pictured at left are just about ready to capture pollen from the air.

   In contrast, the pistillate flowers of protogynous cultivars have already been pollinated. The photo at right shows a cluster of Posey pistillate flowers.  The stigmas of Posey flowers are green in color but note the the upper edges of the stigmas are starting to turn brown and look dry. This is the first sign that these pistillate flowers have received pollen and are on their way to setting a nut crop.

  The pollen sacs on Posey catkins are only now starting to turn from green to yellow (photo at left). It won't be long before these pollen sacs will begin to open and release the pollen needed to fertilize the pistillate flowers of protandrous cultivars like Gardner.

Thursday, May 5, 2016

Pecan pollination season rapidly approaches

   Yesterday, I took a quick trip around the Pecan Experiment Field to check for pistillate flowers (female flowers) on our pecan trees. The catkins or the male flowers have been out for some time but the female flowers are just now starting to show themselves at the ends of new shoots on protogynous cultivars. Lets take a look at the 2016 pecan pollination season as of 4 May 2016.

Pawnee catkins
   The first thing I noticed was that early pollen shedding cultivars (protandrous), like Pawnee, had large fully developed pollen sacs (photo at right). The pollen sacs will eventually turn yellow just before they split open and release millions of pollen grains into the air.

Kanza catkins

    In contrast, late pollen shedding cultivars (protogynous) have long narrow catkins with pollen sacs that are still far from obtaining full size (photo at left). It will be a couple of weeks before pollen is released from these Kanza catkins.

City Park pistillate flower cluster
   The only pistillate flowers I could find yesterday appeared on protogynous cultivars. In looking at several cultivars, I found flower clusters in several stages of development. Pistillate flowers on some cultivars were just beginning to peak out of a terminal's new growth (City Park, photo at right), while others had fully formed flower clusters (Mullahy, photo below). I was very glad to see a good pistillate flower crop developing on my Kanza trees (photo below).

Mullahy pistillate flower cluster

Kanza pistillate flower cluster