Let’s suppose you’ve been foraging acorns for a season or two and are so fond of them you want a food tree in your own yard. By growing acorns yourself, you’ll be able to cultivate varieties that are well suited to your soil and climate and that may be difficult to purchase.
The first step in planting an oak tree is to select large, well-formed, healthy acorns from your favorite parent tree. Experience in gathering the nuts for eating will help you in this respect, as you’ll be able to recognize a suitable seed simply by its sheen, color, and feel. Discard any acorns that sport worm holes or are discolored, and remove the caps from good nuts soon after you harvest them.
Fall is the preferred time for planting acorns, as many cold-climate oaks require a stratification period; that is, the nuts must remain at temperatures just above freezing for at least six weeks — and perhaps as long as 20 weeks — in order for the nuts to germinate. However, if you intend to store the seeds for planting at a later date, you can stratify them yourself: Set the kernels in a moist planting medium such as sand, peat moss, vermiculite, or sawdust and place them in cold storage. The acorns of the white oaks are generally viable for a month or two after ripening, while those of the black oaks are viable for six months or more. Drying the acorns to 60% of their initial fresh weight and then keeping them in cold storage (35-40°F) can lengthen the viability of white oak acorns to about eight months, and similar treatment might further extend the viability of black oak acorns, as well.
Once you’ve collected your acorns, or received them from an acorn supplier, you’ll need to decide on a propagation method.
Chances are that your acorn cache will be limited, so you’ll probably want to grow seedlings in seedbeds, flats, or containers before setting them out in their permanent location. You can even germinate the acorns before planting them in their “nursery” area. To do so, place the nuts about 1″ deep in a plastic bag filled with moist, sterilized potting medium and store the package at 50-75°F. The acorns should sprout in a few weeks. When the sprouting root is 2-3″ long, transfer the tiny tree to a deeper container or seedbed.
- Seedbeds. Planting acorns in seedbeds is quite easy, especially if the timing of the seedlings’ growth allows them to be transplanted directly into their permanent ground. This propagation method is not recommended for evergreen oaks, but it works fine for deciduous species.
- Flats. Growing the seedlings in flats is more labor-intensive than seedbed planting because the small trees must be transplanted more frequently so that the roots don’t become tangled. Use flats that measure 4″ deep or more; if possible, they should have screen bottoms to allow for adequate drainage and to encourage air-pruning of the roots.
- Containers. Starting your acorns in containers is a good method of propagation if you plan on growing only a few trees. A pot at least 2″ x 2″ x 8″ deep is required (gallon vessels work well and are easy to locate). Trees intended for arid areas should be grown in even deeper containers to encourage taproot growth.
The seedlings should be transferred to larger pots before they become root-bound. Because the roots typically grow much faster than the stem, this problem may occur before a great deal of aboveground growth is apparent, so keep close tabs on the progress of your seedlings. And, as when transplanting any crops, gradually harden off the plants before the move and minimize the shock of transplanting by setting the repotted plants in a partially shaded location and by keeping them moist.
Transferring the seedlings to their permanent home should be done when conditions favor growth. Spring is usually an ideal time, but if the autumn rainfall is more reliable in your area, you might opt to plant your young trees in the early fall. Again, harden off the seedlings by reducing water and nutrients and gradually exposing them to outdoor conditions. Supplemental watering during the first year or two will ease your trees’ adjustment to their new home
How They’ll Bear
Acorn production begins three years after planting for some oaks but may take considerably longer for others. As with pecans and other nut crops, acorn yields often vary from year to year. This adaptation, known as predatory sanitation, enables trees to produce extremely high yields in boom years (thus ensuring that enough acorns will survive rodent and insect losses), while the low yields in bust years reduce the insect populations and contribute to thedecline of other predators, as well.
Insects, fungal diseases, and pollutants can substantially reduce acorn yields. Although pesticides are sometimes used to combat infestations, especially in urban areas, many diseases can be eradicated only by destroying the infected tree. For that reason, prevention is by far the best policy. To promote tree vigor, match oak species with their preferred habitat; make certain that sufficient water, nutrients, sunlight, and space are available; avoid accidental injury to the tree (such as cuts, bruises, or broken limbs); encourage natural insect and disease controls as much as possible; and remove and destroy fallen fruit and prune dead or infected limbs from your trees. In the event that chemical controls do become necessary, check with your state’s forestry department or with the nearest office of the U.S. Department of Agriculture Forest Service for information.