Monday, December 30, 2019

Giving pecan trees room to grow

   To maintain good nut production, pecan trees need plenty of room to grow and develop a full canopy. When I established my pecan breeding block, I planted trees far closer than normally recommended to allow for the evaluation and selection of new cultivars. As the trees started to produce nuts, I started to remove trees that produced small nuts or displayed poor resistance to pecan scab disease. This project started with over 800 trees but currently, I've already removed 90% of the original trees.
     This winter, I'm back thinning out more trees (photo at right). At this point in the project, my tree removal objective is to make certain that trees that have the greatest potential to become new cultivars have plenty of room to expand their canopies. The trees in the photo were growing only 20 feet apart within the row (row spacing = 40 feet)  with adjacent canopies shading each other. After tree thinning,  the remaining trees will be spaced 40 feet by 40 feet.

      The photo at left is an example of the nuts produced by one of my selections that I have made a priority for ensuring adequate tree spacing. In fact, tree KT334 is pictured above as the first tree in the row at the left side of the photo. Now that KT334 has a more normal tree spacing, I'll be able to get a better feel for its production potential.

Thursday, December 26, 2019

Preparing pecan seeds for planting next Spring

    Next summer,  I plan to grow some pecan seedlings from seed so I can eventually expand my pecan orchard.  The seed I'll be using this year came from my pecan breeding block and is basically all the nuts that were too big to fit in my pecan cracker (size 15 pockets). I'm sure I'll get a lot of variation in seedling vigor from this seed source but I plan to rouge out any runty seedlings by mid summer.
    Pecan seeds need to go though a process called stratification before they will germinate properly. I start this process by placing all my seed in a large plastic tub (photo above).

    Next, I fill the tub with water and allow the pecans to soak overnight (photo at left). The pecans will float to the top. To ensure that all the nuts stay submerged in water, I place another plastic tub (same size) on top of the nuts then weigh it down with additional water to press all my seed nuts under water. Only fully hydrated seed will sprout into trees.

     Pecan seeds also require a chilling period to release them from seed dormancy. However, the seeds must not be allowed to dry out while in cold storage. To accomplish this, I line the bottom of a plastic storage container with moist potting soil (a mixture of peat moss and pine bark), then place a layer of well soaked nuts on top (photo at right).

    I then cover then nuts with a layer of more potting soil. I make sure all the nuts are fully covered (photo at left).
     Next, I add more pecans on top (photo at right). Once I create another layer of seed nuts, I'll cover those nuts with another layer of potting soil. I repeat the process until the box is full and the final layer of seed nuts is covered by potting soil.
    I ended up getting 4 layers of seed nuts in each storage box (photo at left).
    The final step in seed preparation is to label the seed box with the date the seed will begin their cold treatment (photo at right).  Yes, I was stratifying pecan seed on Christmas day. The sun was shining and it was over 60 degrees outside. I couldn't think of a better present to give my family than the promise of a new pecan orchard.
     The final step in the stratification process is to place the seed boxes into cold storage. Pecan seeds need to be held at 33 to 40 degrees F  for 90-120 days before they will germinate uniformly. If you use a standard household refrigerator to stratify your seed, open the lid of your seed box once a month to make sure the potting soil isn't drying out. If the soil feels dry, simply sprinkle on some water to re-wet.  
    My seed nuts should be ready for planting in late April just as outdoor temperatures start to warm up. 

Wednesday, December 11, 2019

Top-working a pecan: Reasons for failure and an appoach for next spring

    Recently a California pecan enthusiast sent me a photo of his failed attempt at top-work a fairly large pecan tree (photo above). He had found my pecan blog online and solicited my advice on how I would approach grafting his tree. Rather than just replying to his email, I though his photo could prove to be a good learning opportunity for many of my readers.
   I'll start by pointing out why I think things went wrong. From what I can see, 9 grafts were attached to this tree, each covered in a paper bag, and scattered among terminal branches. From the photo, I cannot tell which grafting technique he employed but I do know that every graft failed. The biggest mistake made in grafting this tree was that not enough of the tree was cut back to force a graft to take. Applying a graft out on the end of a branch simply allows too many places for the tree to grow around the cuts made in grafting. Ultimately, the tree just walls off the scion like it was a broken twig. In addition, I am not a fan of placing a brown paper bag over the graft union and scion. Rather than shading the graft as intended by this method, the bag can cause the scion to get too hot, baking in the every present Southern California Sunshine. Thirty years ago, I visited a commercial nursery that was bagging every pecan graft. I recommended dropping the bagging process and their grafting success increased dramatically.

   Now lets look how I would approach grafting this tree next spring. Before making a single pruning cut, I would make sure to obtain some good scionwood cut from a vigorous one-year-old shoot. I would top-work this tree with a single bark graft, so great scionwood is critical. When leaves start to unfurl next spring, this tree will be ready for grafting. In the photo above, I have drawn in the pruning cuts I would make. The cut labeled "A" is the location where I would place a bark graft (directions for bark grafting can be found Here). I would also remove the large 3-forked branch marked "B" to make sure all of the tree's upward growing energy is directed to the graft union. I would leave all the remaining lower lateral limbs in place to shade the trunk and provide valuable leaf area to help feed the root system. In addition, I would also do a little detailed pruning by removing any small branches that are growing strongly upwards (cuts marked "C"). In fact, all summer long I would return to this tree to make sure that the lower lateral limbs only grow outwards not upwards. 
      After inserting a bark graft into the top of the central leader, I would be certain to attach a 8-foot-long training post to the trunk so that it extends 5 feet above the scion. My goal for this tree would be to get 5 to 7 feet of new growth from the scion during the first summer so I'll need a good sized training stick to support the scion and prevent wind damage.