Monday, June 30, 2014

A Tree Race--the Acorn & the Potted Tree (Grimm’s “The Tortoise & the Hare” revisited)

Justin Evertson

We’ve been monitoring a small oak-growing study in Waverly the last few years designed to evaluate nursery growing methods of bur oaks.  Bur oaks were planted from three different growing methods: traditional smooth container, fabric grow bags and direct seeding of acorns collected from oaks growing on the UNL campus. The acorns were planted in fall 2011. Nursery trees planted Fall 2012. Care has been minimal, but the trees were watered during exceedingly dry summer of 2012 and again in 2013. Observations so far:

Plastic Container Trees: Started about 1.5” caliper and 10’ tall. They were all pot-bound, with severe root circling in the container. The roots were not cut or squared at planting time. Significant dieback has occurred on all three plants and the root systems are not yet well-anchored. One is completely dead, the other two are re-sprouting from low on the trunk and would likely not be acceptable to the typical tree buyer.

Grow Bag Trees: Started about 1” caliper and 7’ tall. There was minimal root-circling at planting time. The roots were not cut or pulled out at planting time. There was some dieback from the 2012 drought though not nearly as bad as the plastic container trees. All three root systems appear to be well-anchored now.  All trees are putting out good growth this spring and are finally starting to be taller than when they were planted.

Acorn Seeding: There are six trees total (after thinning six batches of seedlings in late 2012). All have grown quite well. Care included rabbit fencing the first two years and occasional watering during the 2012 drought. Four of the trees are already over 5’ tall and two are over 6’ tall (averaging over 3’/year the last two years). The trees are well branched with strong vertical growth.

Conclusion: Plant the acorns if you can! After this year, it is almost guaranteed that the acorn grown trees will all be taller and more resilient (better established roots) than the nursery grown trees. However, the grow-bag trees are clearly superior to the plastic-container grown trees in this study. Considering that they had to survive the terrible heat and drought of 2012, they have done fairly well and would probably be acceptable to the typical tree buyer/planter.

So far, this study confirms the importance of a good root system for establishing young trees. At the end of the 5th year of growth, most trees will be dug up and roots will be closely examined.
PHOTOS from top: grow-bag roots; plastic container roots; planting site.

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