For the past two years, our farm has been studying the role nursery container depth plays in the initial development of chestnut seedlings as a taprooting tree species through a SARE grant (Project FNE20-947).
We created five experimental container groups: 6", 9", 12", 15", and 24" with 128 seeds per group that we raised in a nursery in 2020. The idea with the 24" group was to simulate conditions where taproot growth was uninhibited. In the second year, we transplanted ~70 of the healthiest from each group into the field. Aerial height, caliper, and root length were measured.
The results were interesting. We found that a shallower container produced significantly more aerial growth in the nursery year (the 6” and 9” groups grew ~4” more than the 12” group, and ~6” more than the 15” and 24” groups). This advantage did not, however, carry over to the field year. As can be seen in the figure below, all experimental groups finished at roughly the same height this past autumn. This means that once in the field, the 12” and 24” groups grew at almost double the rate of the 6” and 9” groups. The greatest gain was made by the 15” group, averaging 2.96” more growth than the 12” group. If this trend continues, the 15” group will average a foot taller than their 12” counterparts by their first potential year of bearing. The difference 3” of soil depth can have - at $.20 additional cost per tree, in our case - may be substantial.
Graph showing aerial height of groups in nursery and field year: Average Aerial Height Growth of Chestnuts (Nursery Year 2020/Field Year 2021) - Album on Imgur
Conclusive results remain to be seen, of course. Perhaps the trees in the 6” and 9” groups took their first year in the field to focus energy on expanding their limited root systems, and will now keep track with the other groups this season. Perhaps the 24” group will gain an advantage over time by virtue of a deeper root system. Time is needed to answer important questions related to survivorship, years to bearing, and overall health. Presently, our field planting is at 98.3% survival with only a single tree in each group dying. How will those numbers look after their first winter?
Photo of chestnut taproot: Chestnut seedling taproot. - Album on Imgur
The final report will be available mid-March on SARE’s website.