By the first day of September all of our pecan cultivars were actively packing kernel into their nut shells. However, when I cut open nuts from different cultivars I still noted differences in the degree of filling. The three cultivars pictured above illustrate some of these differences.
Osage is the earliest ripening cultivar of the three and the nut that has the greatest amount of kernel packed inside the shell. Note that the Osage kernel has expanded enough inside the shell to begin compressing the inner-wall partition that separates the two kernel halves.
The Faith pecan is slightly behind in terms of kernel filling. I can still see a obvious line between the kernel tissue deposited on the dorsal side of the kernel half and the tissue deposited on the ventral side. The inner-wall partition inside this nut is still fairly wide; the kernel has not yet grown thick enough to apply compression pressure.
The kernel tissues of Yates 68 contain both white solid kernel and a layer of jelly-like kernel between upper and lower portions of solid kernel. Air spaces between kernel and the shell can also be seen. Yates 68 is at least 10-14 days behind Osage in terms of kernel filling.
When I cut nuts in cross section to check on kernel development, I also notice big differences in the thickness of green shuck that covers the pecan. The three cultivars pictured above produce nuts with similar shell diameters. But, look at the massive differences in shuck thickness. Gardner has a very thin shuck while the Kanza shuck is very thick. As far as I can tell, shuck thickness does not impact important cultivar attributes such as yield, nut size, kernel percentage, or disease susceptibility. However, after looking at the photo above, I'll never judge a nut by the size of the green shuck again.
Cultivars that ripen in mid-October in our area still have a long way to go to fully fill their kernels (photo above). Lakota and Giles ripen in SE Kansas at the same time each fall, usually around Oct 16. I placed the early-ripening Surecrop cultivar in the photo for comparison. Notice all the air spaces in the Lakota and Giles nuts. These two later-ripening cultivar also have a thick layer of kernel gel inside each kernel half. Giles and Lakota will not finish kernel filling until late September.
