By Peggy Berhenn, UC Master Gardener
- Choose acorns from trees on or near your property. Oaks native to your specific microclimate will have the greatest chance of developing into a healthy long-lived tree.
- Harvest acorns in the fall when they begin turning from green to brown and the caps are easily removed. Uniformly dark, green acorns are not ready for picking. Germination is better when acorns are collected directly from the tree versus from the ground.
- Remove all the acorn caps. Place the acorns in a bucket of water, let them settle for a couple hours. Discard the acorns that float as they are likely damaged.
- Fill a plastic zip bag or a reusable plastic container half full of peat moss, vermiculite, or cactus mix. Acorns can be pretreated with a dilute bleach or antifungal solution to limit mold growth.
- Dampen so the medium is moist, but not soggy.
- Add acorns to the container and leave container slightly open so air can escape, but do not let the medium dry out completely.
- Store container in the refrigerator or other cool place for about 30 days. Refrigerating acorns for a month or more has been shown to increase germination success.
- Check the acorns every week for sprouting and mold. If mold develops, rinse off and place back in refrigerator. Do not let the roots grow too long before planting as untangling long roots can cause damage. Do not plant acorns with completely brown or mushy sprouts.
- As acorns start to sprout, remove them from the medium and plant in a small container root side down with the acorn on its side, stem pointing up. Long tube containers for planting are ideal to support the deep-growing tap root.
- At this point you can keep them in a sunny window or in a protected area outdoors away from hungry squirrels and other rodents.
- They may be fertilized with a slow release 20-20-20 if desired.
- If grown inside, harden off gradually to the outside environment before planting.
- Planting site should be sunny, free of competing weeds, and without excessive gopher or ground squirrel activity. Choose a planting location with space enough for a full-size oak tree.
- Plant outside in their permanent home after the winter rains start (Nov-Jan) and when 2-4 leaves have developed.
- Dig a hole deep enough to accommodate the tap root, which could be 8-12 inches long. Allow the soil to slope away from the seedling and create a basin for watering, mulch around the seedling to retain moisture and inhibit weed growth, while keeping the mulch a few inches away from the trunk.
- Place a 12- to 18-inch-tall protective sleeve around the seedling to protect it from damage.
- Water deeply every two weeks in the absence of rain, or more often if there is a hot spell.
- Keep a 4-foot weed free zone around the newly developing oak tree.
- Do not fertilize newly planted oak as it disrupts beneficial soil microorganisms.
A note about acorn production:
You may notice that some years the oak trees have plenty of acorns and other years seemingly none. Environmental factors play a role in acorn production and vary with oak species. Valley and blue oaks have heavier acorn crops in years in which April temperatures are warmer since this corresponds to pollination time. Coast and canyon live oak acorn production correlates with rainfall from one to two years prior to pollination; more rainfall means more acorns.
References
How to Plant an Oak Tree from an Acorn. How to plant an oak tree from an acorn | Audubon California
How to Grow California Oaks. UC Oaks. UC ANR. How to Grow California Oaks - UC Oaks
Oak Regeneration and Restoration. UC Oaks. UC ANR. Oak Regeneration & Restoration - UC Oaks