Tuesday, April 28, 2015

First pistillate flowers visible

    I took a break from grafting trees to check on the development of the 2015 pecan crop. Every year, our trees are covered with catkins (male flowers) but catkins only produce pollen, dry up, then fall off the tree. Over the years,  I've found that the number of catkins produced has no relationship to the number of female flower clusters that will be produced on the ends of this year's new shoots. So today, I went hunting for pistillate flower clusters.
   The first place I looked was a Kanza tree. I chose Kanza because of its protogynous flowering habit (female flowers receptive before pollen is shed) and if any tree was going to display female flowers early in the season it would be a protogynous cultivar. From a distance, all I could see was more leaves being produced by the shoots (photo at right).
    However, on close inspections I could see a pistillate flower cluster partially hidden behind the petioles of  emerging leaves. The yellow arrow in the photo at left points to the developing flower cluster. As the new shoot continues to grow, the pistillate flower cluster will become more visible with each flower in the cluster developing a prominent stigma. 

Sunday, April 26, 2015

Time for grafting

    The sun was shinning and the temperature was perfect for grafting pecan trees yesterday. I spent much of the day putting scions on seedling trees using the 3-flap graft, arrowhead graft, or bark graft. The method I used depended on the size of the stock tree and the diameter of the scionwood I had on hand.
    Last year, I posted photos of a graft that froze back during the winter of 2013-2014. Rather than re-grafting the tree right away, I decided to let the tree recover and sprout out a new shoot during the summer of 2014. The photo at right shows how the tree looked this spring (2015) with the dead 2013 graft still attached and a stump sprout that developed in 2014 growing out and around the old graft union.
   In this post, I'm going to show you how I re-grafted this tree while giving a few grafting tips along the way.
   The first thing I wanted to show you is how I carry my scions to the field (photo above). I start by filling a couple of 2-liter pop bottles with water and freezing them solid (make sure to leave some air space in the bottle to allow for ice expansion). I use plastic storage boxes to store my scions in refrigeration, making sure to mark the cultivar name clearly on the box. The plastic storage box fits neatly on top of the frozen pop bottles and I'm ready to go to the field and start grafting. 

   Now let's take a closer look at this problem tree (photo at left). You can clearly see where I stapled in a bark graft back in 2013 (left hand branch) and the stem died back to a point just above the new stump sprout.
   My first step was to cut off all the dead wood. A good, sharp pruning saw is a must for a making a cut that angles away from the stump sprout (photo at right).
   In re-grafting a tree, I decided to place my next graft on the fast-growing, stump sprout. This sprout is now the tree's central leader and I can take advantage of the push I'll get by grafting at this apically dominate location .

   Bark thickness was another key factor in my decision to place the graft on the stump sprout. Picking up the parts of the tree I had removed in preparing the tree for grafting, I photographed (at right) the cut surfaces so you can see differences in bark thickness. The smaller diameter limb was cut from the stump sprout while the larger piece was cut when I trimmed out the dead wood on the main trunk. It is much easier to get a tight fit around the scion when the bark is thin and naturally more pliable.
    Sure, I could have cut the tree off below the stump sprout but grafting on a trunk with thick bark takes a little more time to prepare. With a thick-barked stem,  I recommend shaving down the bark with a wood rasp to make the bark more flexible for grafting. 

   On this tree I decided to use a bark graft. The first step in making a bark graft is to make an incision in a straight line down the stock about 2.5 inches long (photo at left). Notice how crooked the stock is on this tree. When making the incision, make sure to draw a line straight downwards ignoring the bends and twists in the stock.

   Next, I moved on to preparing the scion (photo at right). I pulled a piece of Kanza wood out of my cooler and searched for a spot to make smooth, straight cut. The piece I found had a slight curve at the base the scion that I removed with my clippers. After trimming off the bottom of the scion I was left with a good 2.5 inches of straight stem (highlighted by yellow arrow).

    It was now time to start carving my scion. I rotated the scion around to find the straightest place to make my deep cut. Turns out, I made the first cut just above a bud, removing that bud from the grafting zone. I took several more passes with my knife to pare away wood until I got down past the pith (photos at left).
   One detail to notice at this point is that the scion has a uniform thickness but the tongue of the scion has a slight curve to it. We will find that this curve will reappear as a slight problem when we staple the scion into the stock.
    I turned the scion over and started to make the backside cuts (photos at right). First was the angled cut--slicing off just enough bark to expose the cambium and removing another bud in the process. I finished off scion preparation by shaving a 90 degree cut along the wide edge of the scion then carving a chisel point on the end.  (For more a detailed description of scion preparation for bark grafting, see this post).
   I quickly inserted the scion under the bark of the stock along the left side of the incision I made previously (photo at left).  Here's where the curvature in the scion's tongue comes into play.
    After inserting the scion, I had a tight fit along the bottom portion of the graft. However, the yellow arrow points to an air gap between scion and stock caused by the scion's curvature. To close that gap, I used my staple gun. I always start by placing a staple at the bottom of the graft and work my upward. When I got to the air gap, I pressed the scion firmly against the stock and put in an extra staple to hold the scion in place.

    To remove air gaps along the left edge of the scion, I placed staples vertically to press the stock's bark firmly up against the scion. Notice how the bark has been forced to bend inwards to form to the scion. This is why having a nice pliable bark on the stock tree is so important to graft success.
    Once I had the scion in place, I wrapped the graft union with aluminum foil and placed a plastic bag over the whole thing to hold in moisture. The final step was to attach a bird perch to the tree (photo at left).
    I might have a crooked looking tree for a few years, but eventually the trunk will straighten out and I'll be harvesting bucket loads of Kanza pecans.

Tuesday, April 21, 2015

How pecan trees seal off pruning wounds

     Early spring is a good time to prune pecan trees, whether you need trim off lower limbs or make some corrective pruning cuts. Before making any pruning cut, I think it is important to understand how trees are designed to deal with tree wounds.
    First, lets look how a tree deals with healing a wound caused by a broken or dead lateral branch. In the photo at right, a lateral branch has died from lack of sunlight. Look carefully at the branch and you can see the bark is starting to slough off and the wood of the dead branch is starting to decay. However, what is more important to see in this photo is the prominent branch collar that has developed around the base of the dead branch. The red arrow points to the upper edge of live tissue that will grow over the wound that will be created when the dead limb finally rots away.
     When making pruning cuts its always best to work with the tree's natural wound healing strategy. If you prune a limb off at the upper edge of the branch collar, that wound will quickly grow over to seal out wood rotting organisms.  

    Sometimes I'm surprised by the tree wound healing process. The other day I was out in our pecan scionwood orchard and I noticed a tree wound created by cutting scionwood last spring. The original pruning cut was made just above a bud and a new shoot grew from that bud last summer (photo at left).
   The interesting thing I found below the pruning cut was a very distinctive ridge in the bark that angled down away from the new shoot (red arrow). It looks like the tree is trying to develop a branch collar around the pruning wound.
    I took my knife and scratched the bark above and below that bark ridge. Below the ridge the inner bark was green indicating living and growing tissue. Above the ridge was brown and dead tissue.  This summer, the living portions of the bark will continue to grow and the pruning wound will eventually be covered over by new wood.
    Trees do not heal pruning wounds. They simply grow new wood to cover the wound.

Thursday, April 16, 2015

Bud break timing differs between mature and seedling trees

   Recently, I've been posting photos of pecan trees breaking bud. At right is a photo I took this afternoon of a Kanza tree with expanding leaves and barely emerging catkins. Looking the the amount of new growth on this trees has got me thinking its time to start grafting. That was before I went over to look at some of the seedling trees that are scheduled for grafting this year.

    I walked over to a row of Kanza seedlings (rootstock trees grown from Kanza nuts) and was surprised to find that the buds on these head-high trees were only starting to elongate (photo at left). In previous a post, I've shown you the genetic differences in bud break phenology that can be found among pecan cultivars.  Today, by looking a Kanza tree and an entire row of daughter trees, I found that mature, flowering-producing trees start spring growth slightly before juvenile seedling trees. I've also seen this phenomenon occur with fruit trees. A mature apple tree will push out flowers and leaves long before young, non-bearing apple trees start to break bud..
     I might be able to force a 3-flap graft onto the seedling tree shown above but I'd rather wait a bit to start grafting. Waiting will allow me a wider choice of possible grafting methods I can use (I don't start bark grafting until the stock tree has leaves unfurled) and makes finding the right piece of scionwood for each tree a little easier.
   Don't forget to check out the events tab at the top of the page to find a grafting school nearest to you.

Friday, April 10, 2015

Pecan bud break and flowering type

    It seems like spring has come in a hurry and our trees are developing new shoots at a rapid rate. This morning, I photographed emerging buds of several pecan cultivars. I found some cultivars had buds that were just starting to expand while others were already expanding their leaves. I used this variation in bud break timing to create a series of photos that illustrates how protandrous flowering pecan trees (early pollen shed) break bud differently than protogynous flowering cultivars (late pollen shed).

    Today, Surecrop and City Park pecan cultivars were just starting to expand their buds (photo above). At this point in bud development, you really can't see any difference in bud break appearance between the protandrous and protogynous cultivars.

    The buds on Major and Kanza trees had vegetative buds that had expanded to the point you can see leaves about ready to unfurl (photo above). At this point in bud development, the difference between the protandrous Major and protogynous Kanza is readily apparent. Major has pushed out catkins while the catkins on Kanza are still not visible.

     Faith and Lakota trees had leaves that were well developed (photo above). At this point, the protandrous Faith cultivar had well developed catkins while the catkins on the protogynous Lakota cultivar were just starting to emerge from their bud scale coverings.
     As your trees break bud this spring, you might want to check out this phenomenon on your pecan trees.

Tuesday, April 7, 2015

Warm night temperatures advance pecan budbreak

     Last night, overnight low temperatures did not drop below 60 F. Suddenly all the trees in the area look like they are bursting with new spring growth. Pecan trees are no different. Today I found catkins emerging on a tree that has a protantrous flowering habit (photo at right).

    The buds on protogynous flowering trees have also advanced with new leaves poised to unfurl (photo at left). Catkins on these trees are not visable at this time but will soon break out of the two narrow, tapered buds that appear on either side of each central vegetative bud.
    Emerging shellbark hickory buds are massive (photo at right). If you look carefully you can spot two catkins poking out from under a bud scale mid-way along the expanded bud.
   The emergence of new growth in the Spring always gets me excited for the coming season. We'll be grafting soon, followed by a long summer of watching this year's nut crop grow and mature.  

Friday, April 3, 2015

Pecan trees breaking bud

    All week, I've been watching pecan trees as the buds start to swell and the first signs of new green growth appear. What I've noticed is that not all pecan trees break bud at the same time. I'm not talking about the timing of pecan budbreak in Texas vs. trees growing in Kansas. The differences I've noticed this week have been among trees all growing in my local area.    
    Earlier this week, I noticed that the Kanza trees growing on my farm had buds that had split open to reveal just the first glimpse of green tissue. With my interest peaked, I immediately went down to the Pecan Field to check on the progress of Kanza trees at that location. What I found were Kanza trees with buds showing just the initial signs of bud development (photo at right).                    Here was the perfect example of how soil type can impact on early spring tree growth. The tree on my farm is growing in a Cherokee silt loam soil. The tree at the Pecan Field is growing in a Osage silty clay. The lighter the soil texture, the faster a soil warms up in the spring. Spring root growth is stimulated by warm soil temperatures and once the roots start to grow, bud growth follows shortly there after.
    In walking around the Pecan Field today, I spotted the obvious differences in bud development among pecan cultivars (photo above). Greenriver seems to be among the earliest trees to break bud while Chetopa was just barely splitting the outer scale.  By the time we get to pollination and nut set, the differences in budbreak date I observed today, will be totally indistinguishable.  However, all you need to remember is that last year we had a late spring frost that injured early leafing trees far more than the late leafing trees.