Is it time to graft pecans?

    Yesterday and today, afternoon temperatures climbed into the low 80's (F). It finally feels like spring and I'm getting the urge to graft. But wait,  the weatherman is promising us another blast of cold temperatures by the end of the week.  Friday morning's low is predicted to drop to 34 F. Should I wait a while longer before grafting?

     This year's spring-temperature roller-coaster has got a lot of people wondering just how they can determine the best time for grafting. This morning I walked out to a row of seedling pecans to check on their readiness for grafting. The photo above shows you just 5 of the trees I found (click on photo to enlarge). These trees are all Kanza seedlings so the wide variation in bud development caught me by surprise. As I have mentioned in a previous post, it seems like this year's cool spring has stretched out the pecan bud development process.
     Of the trees pictured above, trees A and D are ready to graft by using the 3-flap graft or bark graft. Trees B and E can be grafted with a 3-flap but they have not progressed far enough for a bark graft. It too early to graft tree C.  My personal preference is to wait a little bit longer before grafting. When I go to the field, I want to be able to graft every tree in the row and have all grafting technique options available to me on each tree. This way I can choose the best method for grafting depending on the size of my stock tree and the diameter of the available scions.
    If you are wondering if cold temperatures will reduce grafting success, the answer is no. The scion will just hang out on top of the stock during a cold snap just like it was still in the crisper of the refrigerator. Once warm temperatures return, the callusing process will begin and the graft will progress normally.  On the other extreme, temperatures above 90 F can "cook" a recently applied graft and cause graft failure.

Hickory bud development

 

Scholl shellbark hickory

 

    Over the past few weeks, I've been showing you photos of pecan tree bud development. However, hickories put on a more impressive display of spring bud growth (photo at right). Shagbark and Shellbark hickory produce huge terminal buds. The inner scales of these buds enlarge during bud elongation, then curl back to reveal the new shoot growth. At this time of year, these inner scales almost look like flower petals. They appear light green in color but develop a reddish tinge on the outer margins as they age.

  

    Hickory buds go through all the same growth stages as pecan buds. The photo at left shows a Yates shagbark hickory in the bud elongation stage. Note that the true hickories have numerous bud scales that overlap each other in a spiral fashion around the emerging shoot. Pecans buds develop a single inner scale around their new shoots.
 

      The hybrid of pecan and hickory, also known as a hican, breaks bud more like a hickory than a pecan (photo at right). Hicans produce some overlapping bud scales but these scales do not expand to the large size or create a flower petal type appearance that we see with the true hickories.

Cold overnight temperatures slow pecan tree development

     I woke up this morning and immediately checked the temperature outside. The morning low was 33 F with a brisk northern wind that made me question if winter was making a come back this week.  Later this morning, I checked the pecan trees for any signs of cold damage. Emerging catkins and shoots were are still healthy and green (photo above).
     Cold overnight temperatures this spring have really slowed pecan leaf burst. At this point, I'm pretty sure our grafting season is going to be significantly later than normal. How late will depend on when we finally start getting warm overnight temperatures.
   

    There is one advantage to watching this Spring's slow-motion leaf burst. You can definitely see  differences between protandrous and protogynous pecan cultivars (photo at left).  Protandrous cultivars shed pollen early in the pollination season and before their pistillate flowers become receptive. At this time of year, protandrous cultivars seem to be covered in emerging catkins while new shoots are only beginning to emerge. Shepherd is a protandrous cultivar.
    Kanza is a protogynous cultivar. Pistillate flowers on protogynous cultivars develop early in the polination season becoming receptive to pollen well before late developing catkins begin to release pollen. In the photo above, I've pointed out a Kanza catkin that is only now emerging. Most of the active new growth on this Kanza stem is developing vegetative shoots.  Pistillate flowers will develop at the ends of these new shoots.      

Pecan budbreak advancing slowly

Leaf burst on Greenriver 17 April 2013

   I checked on our pecan trees today and found that bud development is progressing but at a very slow pace (photo at right). The weather this year has been wild. We get 2-3 days of warm, spring-like temperatures then we plunge right back into the cold of late winter. Luckly, the temperatures have stayed above 30 F and we haven't observed any cold injury to emerging buds.
    

Leaf burst on Osage 17 April 2013

    As bud development continues, you can start to pick out those cultivars that shed pollen early (protandrous flowering). Catkins on the Osage cultivar are plainly visible (photo at left). Compare the protandrous flowering habit exhibited by Osage buds to the emerging buds of the protogynous flowering Grennriver cultivar pictured above. The catkins on Greenriver have yet to make their appearance.

Bud elongation on Kanza 17 April 2013

     Kanza and most of our other pecan cultivars are still in the bud elongation stage of development (photo at left).   Chetopa, Giles, Norton, Niblack, and Jayhawk were all in the bud elongation stage. 

What's in my grafting box?

    The pecan tree grafting season will soon be here. Before I cut a single tree,  I like to gather all the tools and supplies I'll need in a handy tool box that can easily be taken to the field (photo at right). I've used this box for over 30 years and what I really like about this particular box is the pull out drawer where I can store extra tools, parts and supplies. Let's take a closer look at what I carry along for grafting pecan trees.

    First are the tools (photo at left). I use a model 605 Tina grafting knife with high-carbon steel blade (A). This is only the second Tina knife I've owned. The first one was unfortunately planted in a pecan orchard a couple of years ago.
    Grafting knives are beveled on one side of the blade while the other side is flat. This is important to remember because when you sharpen a grafting knife it is sharpened like a chisel or wood plane blade rather than a standard kitchen knife. I carry a pair of Felco Model 8 pruning shears (B). I've had this pruner long enough to wear off the red plastic coating on one side of the shear (it now sports a coat of black electrical tape). I install a new blade in the shear each spring. Also in my box is a Model A700 Leonard folding saw (C). I love this type of Tri-edge tooth pruning saw. They cut smoothly and rapidly on the pull stroke. For bark grafting, I use an Arrow Model JT-21M medium duty staple gun (D). The staples inside are 5/16 inch in length. And finally,  I use a wood rasp (E) for removing the rough bark from larger trees during bark grafting.
  

    Next, I carry a collection of consumable supplies (photo at right).  I use a lot of green grafting tape (A). This stuff is actually sold as "plant tie ribbon" and is 1/2 inch wide and 4 mils thick. I use black electrical tape (B), not for grafting, but to install a bird perch on every graft I make. I hate it when birds ruin a perfectly good graft. Elmer's glue, aluminum foil, and plastic sandwich bags are all carried in my box and are used to protect grafts made out in the field. 

    Down in the drawer, I take along some extra tools and supplies (photo at left). I carry a set of Arkansas stones and bottle of light oil (A) in order to keep a keen edge on my grafting knife. If I'm grafting a lot of trees, I usually stop to sharpen my knife about once an hour. I can also use the stones to sharpen the blade of my pruners. For emergencies,  I carry an extra blade for the Model 8 Felco (B), an extra spring (C), and the little tool (E) used to tighten the clippers. Since you never know when a grafting knife can disappear, I always carry an extra knife (D). Finally, I use a lot of staples in grafting, so I carry one or two extra boxes.

    One last item that many people forget in their grafting box are tags and ball point pen (photo at right).  I use  double surface aluminum tags to label the cultivar name on each tree I graft. Using a ball point pen, I can make an impression in the metal with the cultivar name then staple the tag to the tree. The tag will last one season, sometimes two. I install more permanent tags later in the year on successfully grafted trees.

Warm night temperatures advance pecan bud break

  

Greenriver bud elongation 8 Apr 2013

    When it comes to spring-time bud development, warm overnight temperatures are needed to really kick start a pecan tree. For several days now,  we have had overnight low temps in the 50's, so today I went out into the grove to check things out. Our Greenriver trees had passed the inner scale split stage and moved into bud elongation (photo at above). It was only last week when I couldn't find any evidence of bud growth past outer scale split. Wow, things have changed fast.
   

Chetopa inner scale split 8 Apr 2013

    In walking through our cultivar trials, I found trees in several stages of bud development. I decided to photograph these stages so you can become familiar with the terminology used to describe spring bud growth of pecan trees.
   At this point in time, most of our native trees have entered the the outer scale split or moved into the inner scale split stage. Chetopa, a cultivar that originated as a native seedling at the Pecan Field, exemplifies many of our natives in terms of bud development (photo above).

    When looking at pecan tree bud emergence, you will soon come to realize that the terminal bud on each branch pushes opens first with all the buds below at earlier stages of bud development. A Kanza twig illustrates this normal pattern of variation perfectly (photo at right).  The terminal bud is in the bud elongation stage. The third bud down is in inner scale split, while the outer scale of fourth bud has split and fallen off but the inner scale is still intact.
   

Osage bud elongation 8 Apr 2013

    Osage is a cultivar that sheds pollen early (protandrous). In the photo at left, take a close look at the terminal bud. What looks like 3 buds developing from a single location is actually three different structures emerging from a single terminal bud. An elongating vegetative bud is located in the center. This bud will grow into a new shoot that will terminate in a pistillate flower cluster. The two lateral buds adjacent to the vegetative bud contain this years crop of male flowers or catkins.

Late spring in the pecan grove

  

    It looks like we are going to have a late Spring in 2013. This afternoon the sun finally broke through the clouds and I went out to the pecan grove to check on bud development. Our trees seem to be in a holding pattern waiting for warmer weather. The photo at right is a Lakota terminal that shows the first signs of spring bud swell--a stage we call outer scale split. This photo was taken today but our trees were in the exactly same stage of bud development 2 1/2 weeks ago when we fertilized our pecan grove.
    It is  interesting to compare the timing of this year's bud development to the early spring we experienced in 2012. On March 26, 2012 I was photographing pecan trees that had buds in much later stages of bud development; from inner scale split to leaf expansion. Last year spring came 3 weeks early, this year things are going to leaf out late. How late?  We will have to see.
   

    One thing I know is that hickories and pecan/hickory hybrids (hicans) generally break bud 7 to 10 days before pecan. So I decided to check on the hickories. My first stop was a Grainger shagbark hickory (photo at left). This true hickory had also entered the outer scale split stage but showed no signs for further bud development.
   

Interestingly, our Henke hican had not even started bud swell and was still fully dormant (photo at right). I wonder if this will be one of those unusual years when pecans and hickories break bud and flower at the same time. We know that it is possible for pecan and hickory pollination to coincide at times because that is how naturally occurring hybrids develop.

Shell shape can limit percent kernel

    In looking over nut samples from this year's nut evaluation, I noticed a particular pecan shell characteristic that seems to limit percent kernel. Its not what you might be thinking. Yes, shell thickness is obviously an important determinate of pecan shell-out percentage but the shape of the shell can also impact percent kernel. Take a look at three seedling pecans (photo below).

      These three pecans share a common pecan shell trait; they all have an extended apex (marked by the bracket above). The extended shell apex looks like the hand of God just pulled on the tip of the shell and stretched it out. Inside a pecan's shell, the kernel is oriented with the connection between the two kernel halves (and the seed's embryo) closest to the apex. When the apex is extended like the three examples above, kernel doesn't grow up into that region at all.    

     Here's a photo of a St. Genevieve nut that I've carefully peeled away the shell to reveal the kernel (at right). I placed an uncracked St. Genevieve nut in the photo for comparison.  Notice that the entire extended apex of this nut is composed of shell and packing material.  The kernel starts well back from the apex.
    Even if a nut has a thin shell, the pecan that has the extended apex characteristic produces a lump of heavy and unproductive shell at its tip.  Pecan cultivars that share this shell shape usually produce 44-48% kernel.  Cultivars blessed with exceptionally thin shells and cursed with an extended apex will produce 50% kernel at best.
    Other cultivars that share the extended apex trait include Goosepond, Colby, and Niblack.