Monday, May 17, 2021

Pecan pollination underway

Kanza catkins and new growth
    During mid-May I scout my pecan orchard for the intensity of pistillate flower production on new branch terminals. If I find a flower cluster on nearly every shoot, I expect a good nut harvest come this fall.

   The amount of catkins produced by a tree has no bearing of the nut crop produced in the Fall. Although large amounts of wind-blown pollen is necessary to fertilize a large pistillate flower crop, there never seems to be a shortage of fine yellow pollen grains floating in the breeze during the month of May (in our area).

Kanza pistillate flowers
     Pecan pistillate flowers (female) are found on the very terminal end on the current seasons new growth. Each flower in the cluster has a prominent stigmatal surface that is designed to capture pollen grains out of the air. Each stigma has two horns and features a very rough surface. The stigmas of Kanza flowers are green. However,  stigma color among pecan cultivars can varyfrom green, to orange, to red. Since insects are not required for pecan pollination, stigma color has no impact of pollination success. 



Pecan trees have one of two flowering habits. Trees that release pollen before their female flowers become receptive, have a protandrous flowering habit. Trees that produce female flowers that are receptive to pollen before they release their own pollen are termed protogynous.  Today, I found several protandrous cultivars had started releasing their pollen. You can tell pollen is being released because the pollen sacs on the catkins have split open and are turning brown. Gardner pecan, as seen in the photo above, was  releasing pollen today.  

    Pecan trees have developed this dichogamous system of  flowering to prevent self pollination and inbreeding depression.

    If you would like to discover the flowering type of your pecan trees, simply collect some catkins from each cultivar. The first thing you will notice is that catkins are produced in clusters of three. Even before pollen release you can identify flowering type by the shape of the catkins produced. Catkins of protandrous cultivars are short and fat while the catkins of protogynous cultivars are long and narrow (photo at left).

Monday, May 10, 2021

Grafting a frost injured tree

    In spite of a cooler than normal Spring, my pecan trees have started to re-bud following the April 21 frost. The photo at right show the terminal of a young pecan tree that is pushing out new green shoots from secondary buds just underneath frost-killed primary bud shoots. This was the signal I was waiting for to start grafting again.

   In choosing trees to graft, I select young trees that have made vigorous shoot growth the previous growing season. The tree pictured at left was about 6 feet tall and a perfect size for bark grafting. 

    When folks are just learning to graft pecan trees, they often wonder if there is a proper height to make the graft. When I graft, I choose the height based on two criteria. The diameter of the stock should be no larger than 3 inches in diameter and height should comfortable for making grafting cuts. On smaller trees, like the one pictured here, I'll cut off the stock at about 18 inches off the ground or at perfect height for me when sitting on my cooler to graft. On larger trees, I'll cut the stock at chest high to make grafting while standing more comfortable. Either way, I always remove at least 2/3 of the stock tree's height to force the tree to accept my graft.

    Once I choose the approximate location for cutting the stock, I carefully inspect the trunk for any a major knots or pruning wounds. On the tree I've selected to graft, I found two pruning wounds on either side of the trunk (photo at right). Underneath those wounds, the bark was nice and smooth, an excellent site for bark grafting.

    To make scion insertion under the bark easier, I cut the stock just below the two pruning wounds (photo at right).
    Once I prepare the stock by making a vertical incision in the bark, I turn to carving the scion. The photos at left show the cuts I make into the scion. The first cut is a deep cut to narrow the width of the scion to allow it to slip under the bark of the stock. Next, I make a shallow cut to expose the cambium on the back of the scion. This cut is made at an angle to deep cut. At a right angle to the deep cut I peel away a sliver of bark to expose cambium along the edge of the scion that will abut the verticle incision I made in the bark. My final cut is to carve a chisel point into the end of the scion to facilitate insertion under the bark. A detailed description of this grafting method can be found HERE.

  Once the scion is prepared I can quickly insert it into the stock and staple it into place. First, I place a row of staples up the incision of the bark. These are places at an angle so both sides of the staple sit firmly against the bark. Then I place a verticle row of staples just to the left of the scion to press the stock's bark up firmly against the shallow cut I made on the backside of the scion.

   To complete the grafting process, I wrapped the graft union in aluminum foil then covered that wrap with a plastric bag tied both on the scion and the stock (using green tape). I placed a drop of white glue on top of the scion to seal in moisture then attached a bamboo stake to the tree with electrical tape to prevent bird damage and provide support for the growing scion. My final step was to label the graft with an aluminum tag imprinted with the cultivar name.

     When completed, my grafted tree looks tiny compared to the stock tree I started with. In the photo at right, I layed the severed top of the tree next to the graft to give you an idea of how much I pruned off.  This may look like drastic surgery but when this graft takes, the new shoots will grow rapidly attemping to replace all that wood I pruned off. In addition, a fast growing tree is easier to train to central leader.

Sunday, May 2, 2021

Grafting after a late season freeze

     Most years I start grafting pecan trees around the first of May. The photo at right shows a young seedling pecan tree that is the perfect size to graft using a 3-flap graft. For field grafting, I use growth stage as a gauge for when grafting will be most successful. The tree in the photo has new leaves just starting to unfurl. The emergence of new leaves tells me that the bark will easily slip which is so important for 3-flap grafting.

    After 40 years experience in grafting trees, the first graft of the season went on perfectly (photo at left). If you need a refresher on how to make a 3-flap graft check out my post HERE. As always, I placed a bamboo stake next to the graft to provide a bird perch (prevents graft breakage from birds) and a support stake for the new growth that will emerge from the scion.


    However, much of my grafting will be delayed by the freeze we suffered on April 20. The photo at left shows one of many young trees that had their emerging buds frozen by the cold. The cold temperatures killed all emerging green tissue turning it brown. This shocks the tree into delaying further spring growth for at least a couple of weeks. As I said before, I like to wait until I see new green leaves before making a graft. 

    Following late spring frosts experienced in the past, I patiently waited until secondary buds on the young trees started growth. I ended up grafting a couple of weeks later than normal but I still had good success. I'm hoping this year will be similar.

    I took a close-up photo of a frost damaged seedling tree (photo at left). You will note that all of the primary buds on this stem were frozen. However, the secondary buds have already started to green up. The red arrows in the photo point to easily visible green buds.  These buds will take a little while to fully develop and break into new leaves but I expect to be grafting in 7 to 10 days. The speed of bud development will depend on the weather. Warm temperatures and sufficient rainfall should push thing along.