Tuesday, January 3, 2017

Stratifying pecan seed

   The beginning of a new year usually inspires folks to make plans for the future. I can't think of any better plan then to plant more pecan trees. So the very first thing I did in 2017 was to start stratifying pecan seeds that I plan to grow into new trees this summer.

   Stratification is the method we use to promote uniform seed germination. The process involves getting the seed nut fully hydrated then storing the moist seed in temperatures between 32 and 40 degrees F (0 to 4 degrees C) for 90 to 120 days. I started the process of stratification by placing some Giles pecans (2016 crop) into a 5 gallon bucket (photo above right).   

   I then added enough water to float the nuts inside the bucket (photo at left). To make sure the seed inside the shell becomes fully hydrated, I like to soak the nuts for 24 hours .

   To keep the nuts that float wet during the entire 24 hour soaking period, I placed a second 5 gallon bucket inside the first bucket and on top of the nuts (photo at right). By adding water to the upper bucket, the weight of the upper bucket presses down on the nuts below and keeps all seed nuts fully submerged.

    After 24 hours, I drained off all water from the seed nuts. As a precautionary measure, I added some Captan fungicide to the wet nuts and stirred the nuts around until each nut was coated with the white powder (photo at left). The fungicide will act to prevent kernel rotting fungi from destroying seeds during the cold stratification process.

    I use plastic storage boxes for seed stratification. I start by placing a layer of potting soil in the bottom of the box (photo at right). The potting soil is damp (not dripping wet!) and about 1.5 inches deep. By using damp potting soil, I ensure the nuts stay fully hydrated during the entire cold storage period.

  Next I add a single layer of nuts to the box (photo at left).

   I then add another layer of moist potting soil over the top of the nuts. At this point my small storage box was full and ready to be refrigerated. I you choose to use a deeper storage box, multiple layers of nuts can be added to the box. Just make sure to add potting soil between each layer of seed.

   One reason I like to use storage containers for stratifying seed is because the lids fit tight enough to prevent moisture loss during cold storage.  I place a label on each box with the cultivar name and the date the nuts begin stratification (photo at left). To achieve uniform germination pecan seeds need at least 90 days of cold temperatures. I use a standard household refrigerator to treat the seed and set the temperature to 34 degrees F (1 degree C).
    By April 2nd, these nuts will have had 90 days of cold treatment. However, I don't like to plant seed into pots until the danger of frost has passed. At my location, the average frost free date is April 20th. With an extra couple of weeks in the cold, these seeds should pop up quickly after planting.