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Growing Oak Trees from Seed
By Guy Sternberg

(excerpted from “Legacy in a Nutshell,” September/October 2000, The American Gardener)

In temperate North America, [acorns] ripen in late summer or autumn and should be gathered as soon as they fall for use as seeds. Better still, pick them from the tree just before they drop, so they don’t lie on the ground and bake in the sun or become infected with fungi. Select nuts without any noticeable insect or disease damage, and cut a couple open to make sure they are not hollow from insect feeding or lack of pollination. Avoid those that fall much earlier or later than the majority from the same tree. Store [acorns] in labeled plastic bags and keep them refrigerated - but not frozen - until planting. Don’t allow them to dry out, other than brief surface drying to retard fungus growth.

Planting Options

Most nut tree seedlings form long taproots early in their development. This is great for a seedling germinating in its permanent home, but not so good for one that is growing in a pot or that is destined for transplanting a year or two down the pike. You have several options for dealing with this; select the one that suits your planting situation and personal convenience.

1. Plant the seeds directly into their permanent location in holes a little deeper than the thickness of the nut.
    

2. Pregerminate the seeds by cold conditioning until the radicals - the embryonic roots - emerge. [Note: oaks do not require any pregermination treatment with the exception of red oak, which responds to cold conditioning.] Then clip the tips of the emerging radicals prior to planting, causing them to branch into a fibrous root system. Plant them in an outdoor seedbed where they can be kept for two years, or in a suitable container system where they usually are best kept for a single year.
    

3. Whether or not you clip the radicals, use copper-treated root-control containers, bottomless containers placed on elevated mesh benches, or other techniques to keep the taproots from extending too far or circling in a container.
   
   Bottomless containers allow the roots to grow straight down out of the pot so they do not begin to circle. As they grow out the bottom and into the open air, their tips dry out and die. This technique - known as “air pruning” - forces the root to branch out inside the pot.
    

4. You can plant [acorns] in deep pots if you transplant and root prune them during the first year, before the roots reach the bottom. I prefer shallower, bottomless pots - used with the techniques mentioned above - to encourage a fibrous root system that will establish better when transplanted.