Pecans don't grow true from seed

    Over 30 years ago, we planted Giles seedlings in our pecan grove to help fill in the gaps that existed among much larger native pecan trees.  Since that time, the trees have grown and matured into nut bearing trees. In the photo above, I have outlined a pair of Giles nuts. The rest of the nuts in the photo were harvested from the Giles seedlings. Note that not one of the nuts produced by the seedlings looked exactly like a Giles nut.
    The Giles seed we used for these trees dates back to the 1980's and originated from our field trials at that time. Since pecan is a wind pollinated crop, the pollen parent for these seedling trees could have been anything from a native tree to a large improved cultivar such as Mohawk or Maramec. Its obvious from the photo above that some of the seedling trees received  some "large nut" genes from the pollen parent.

     The table at left provides some additional data on these Giles seedlings. For the 2014 crop year, our Giles nuts averaged 6.36 g/nut and 52.66% kernel. All but one of the seedlings produced nuts that were smaller than the parent tree. Only four seedling trees produced nuts that had higher percent kernel than the Giles parent.
    Of all of the seedling trees, KS800 has consistently produced nuts with outstanding kernel quality and appearance. However, this tree has 2 negative traits. It has an upright growth form that produces numerous narrow angled branch connections. But more importantly, the tree is a light nut producer.

     The moral of this story is that it is very difficult to find outstanding new pecan cultivars by just growing out some open-pollinated seed. We planted these trees in our native grove knowing full well that we wouldn't discover a new "super Giles" tree. We did, however, establish some new trees in our native grove that preserved the genetic diversity of our tree stand while improving the average percent kernel of our native crop (natives average 45% kernel, the Giles seedlings averaged 50.64% kernel).

Our pecan seeds are up!

   Last fall we acquired an old Truax tree seed planter in need of repair and re-engineering. This simple machine reminds me of a larger version of a single row corn planter but capable of handling much larger seeds such pecan. We worked on a redesign of the nut metering system and gave the planter a test run last fall (photo at right).
   The planter works best in a well prepared seed bed as shown at right. To make sure we planted the nuts in a strait row, we stretched a string across the field and planted following the string with the front right tractor tire.
   To establish this planting, we harvested early-ripening Peruque nuts, cleaned the seeds, then planted in late October. After planting the pecan seed, we planted a cover crop of winter wheat between the tree rows to hold the soil during the winter and following spring.

    This week, a well defined row of pecan seedlings have popped out of the ground (photo at left). Prior to pecan seedling emergence and before the wheat started to joint, we marked the tree row with a string and sprayed a mixture of roundup and pendimethalin (pre-emergence herbicide) over the top to suppress weeds.
    We plan on leaving the wheat in place throughout the spring flooding season to hold the soil.  Over the summer, we'll spot treat weeds in the tree row with herbicides and clean till the area between rows.
    In using the tree seed planter last fall, we discovered that the furrow closing system currently on the machine does not work in our heavy textured soils. Soil becomes compacted around the shoe of the planter and seeds back up in the drop tube. To plant last year, we removed this ineffective furrow closing system and planted the seed without it. Look at the photo at the top of this post and note that the planter left a V-shaped trench in the soil. This summer we'll be installing two discs on the machine to close this furrow.
    Once we get all the bugs worked out on the planter, we will be leasing the planter to area growers interested in direct seedling new pecan orchards.

Seed source for northern pecan rootstocks

    Its the time of year for stratifying pecan seeds. Most northern pecan growers understand that cold hardy rootstock trees are produced from seeds of northern pecan cultivars. Graft a northern pecan cultivar on a southern pecan rootstock and you may find that the tree below the graft union will freeze during a test winter.
    Over the years, we have used several seed sources to grow trees among them Giles, Kanza, Posey, and Colby (photo above). For years, Giles has been recommended for northern growers but why?  Is it really better than other northern seed sources?  Is there a better northern seed source?
   Whenever you plant pecan seeds, the trees that germinate can be very variable in terms of  vigor and disease resistance. Planting a known cultivar only guarantees you know the female parent--the male parent just flew in on a spring breeze. So in choosing a northern pecan cultivar to plant, its best to collect seed from a northern orchard where all possible male parents have a high level of cold tolerance.
 

 
    Now lets talk cultivars. The photo above shows a cross section of four pecan cultivars we have used as seed for nursery trees. Note how the Giles seed is poorly filled as compared to the others. Poorly filled Giles kernels are all too common because this cultivar is susceptible to both over-production and pecan scab (both problems reduce kernel quality).  Even if a pecan is poorly filled, the seed can still germinate and grow into a tree. However, seedlings from poor quality nuts have low seedling energy and struggle to grow in height and girth especially during the first year. Slow seedling growth rate translates into a longer wait to graft and a longer wait until nut production.
   Giles seeds also have a hidden defect not easily recognized. Pollen shed and pistillate flower receptivity overlap in Giles. This overlap leads to partial self-pollination and the production of nuts that, when germinated, demonstrate in-breeding depression.  In the nursery, self-pollinated nuts show up as "runts" and Giles seems to produce more runts than other northern seed sources.  Slow growth rate and an excessive number of runts has made me abandon Giles as a seed source for my nursery trees.

Kanza seedlings

    What seed source do I recommend? Kanza and Posey seeds generate aggressively growing seedlings under commercial nursery conditions. Colby seeds grow well but seedlings seem to have a higher degree of susceptibility to disease, requiring greater reliance on a season long fungicide program.
   Last summer, I grew out a couple hundred Kanza seedlings (photo at left). For the most part I was pleased with the results but still had to cull out the occasional runt. Heartlessly culling out under-performing seedlings will leave you with uniformly-vigorous rootstock trees that preform well when planted in the field.  A genetically strong rootstock increases scion growth rate and decreases the wait until nut production.

Container grown pecan trees: Fall planting and overwintering potted trees

   For the past three weekends, I've been planting the pecan seedlings I started in containers this past spring. Fall is the perfect time for planting container grown trees (photo at right).  For the most part, the soil has just enough moisture to make digging the planting hole easy but is dry enough to allow you to back fill the planting hole with loose, friable soil. Fall planting also allows the roots of the young tree to begin growing out into the surrounding soil almost immediately, helping to decrease transplant shock.

      The trees I planted this fall averaged about 10 to 12 inches in height with an air-pruned root system only about 4 1/2 inches deep (photo at left).  The depth of the root system makes it very easy to transplant--one shovel full of soil and I've got a hole deep enough for the tree. I like to to plant these trees about an inch deeper than they had grown in the container, allowing the root ball to be fully covered with soil. Planting deep ensures that the soil-less media that still surrounds the root system is not directly exposed to drying winds and the tree doesn't desiccate.

     The photo at right gives you a good look at the type of root system that develops inside the bottomless container. The tap root has been air-pruned forcing the development of  a network of fine lateral roots. Once this tree is planted in the field, the air-pruned taproot will re-sprout often creating two or three new "taproots". Next year, my transplanted seedlings will put on just a few inches of new top growth but more importantly, they will be developing massive root systems designed by nature to ensure tree survival.

     I planted about 150 trees this fall but still had some trees left over. With winter's first blast of arctic air forecast for this week, I took some steps to protect my remaining potted trees from the big chill. Although pecan trunks and branches can stand temperatures down to -26 F, the roots of pecan trees will freeze at about +19 F.  This means I needed to take some steps to protect the roots of my remaining potted trees.
    I moved the trees from the nursery bench into my vegetable garden. The garden has two things that makes in perfect for overwintering trees. First, we have raised beds in the garden and the garden paths are just the perfect width for a flat of trees. With a raised bed on either side of the flat, it looks like the trees are partially buried in the soil (photo above).  The garden is also surrounded by a fence that will keep the trees safe from mid-winter rabbit feeding.
    To prevent root freezing, I used a thick carpet of hay packed around the tree flats to insulate and trap the soil's heat around the trees (photo below). 

Pecan seedlings produce simple leaves

    In yesterday's post on growing pecan trees in containers, I presented a photo of nicely-growing, tree seedlings. A copy of that photo is published at right.  Look closely and you'll see that the leaves on these trees don't look like the compound leaves we usually see produced by pecan trees.  The leaves on these seedling trees are simple, appearing as a single elliptical leaf. Are they really pecan trees?
   

   The answer is yes! The first few leaves produced by emerging pecan seedlings are always single bladed. Today, I took a photo of one of my seedling pecan trees (still in the pot) and a normal compound leaf pulled from a three-year-old seedling (photo at right). The leaves don't even look like they come from the same species of tree. However, the seedling in the container will begin to produce compound leaves as it continues to grow. The first compound leaf might have just 3 leaflets, but as additional leaves are produced the number of leaflets will increase.  Eventually, my container grown seedlings will starting looking like "normal" pecan trees.

Stratifying pecan seeds

    If you have even considered growing pecan trees from seed, the nuts will need to go through a process called stratification before they will germinate properly. Stratification is a simple process that involves soaking dry seed in water then storing that wet seed in a cool moist condition for 90 to 120 days. With stratification we are basically mimicking what happens in nature. A squirrel buries a pecan in the soil during the fall where it remains cool and moist all winter long. The squirrel-planted seed doesn't germinate until the following spring when the danger of frost has past.

   Here's how I stratify pecans for next year's planting.  First, I place new-crop nuts in a plastic container, filling it about 1/2 way. I then fill the box with enough water to cover the seeds and let the seeds soak overnight (photo at right). You will need to stir the nuts around in the water  once in a while so the nuts on top don't dry.

   After soaking. I add a moisture holding media to the nuts and water. In the past I've used peat moss, cedar shavings, potting soil or saw dust. This year I had plenty of saw dust on hand, so I mixed the dry saw dust into the nut and water mix (photo at right).  I used enough sawdust to surround the nuts and soak up much of the free water. I let the saw dust soak up the moisture for a few hours then pored off any excess free water out of the box. I then placed the tight-fitting lid on the box and placed the box in the refrigerator.
    For the stratification process to work effectively, the nuts should be held in cold storage at between 32 and 40 F (typical refrigerator temps). For northern pecan cultivars, germination is more uniform when nuts are held a full 120 days in stratification. By stratifying nuts now, you will have nuts ready for planting by May 1st, a perfect time for planting pecan seeds.