If you have the space, planting a native oak in your yard is one of the best things you can do for wildlife. Growing an oak from acorns collected nearby has the advantage that you know the tree is well adapted to your local growing conditions.
Starting an oak from acorn is always done outdoors, either in a seedbed or in pots. Because pots give you better control over the growing process and it’s also easier to protect the acorns and young seedlings from critters, growing them in pots is your best bet.
When and How to Collect Acorns
When you are in on the lookout for acorns, keep in mind that the acorn production varies by oak species and also depends on the weather, nutrient availability, and insects feeding on acorns. While most oak species produce a good acorn crop every two or three years, white oak (Quercus alba) only produces a good acorn crop every four to six years.
The acorns of some acorn species—white oak, swamp white oak (Quercus bicolor), and bur oak (Quercus macrocarpa)—mature in one year, while for other oaks—red oak (Quercus rubra) and pin oak (Quercus palustris)—it takes two years.
Only collect acorns that have fallen from the tree; only these acorns are mature. Skip the first ones that drop, as they are often of poor quality. Collect them once the tree drops a lot of acorns and do it promptly because acorns dry out quickly and then become inviable. Remember that you're competing with squirrels, deer, and other wildlife; if you wait too long, there might not be many acorns left.
Collect at least twice as many acorns as the number of seedlings you want because not all of them will germinate. Discard acorns that still have the caps attached, that have holes or are otherwise damaged, or show signs of mold or rot.
Plant the acorns right away; if that’s not possible, you can store them for a few days. Spray them with water to prevent them from drying out and place them in a plastic bag that lets some air in. Store them in a cool place and keep them moist but not wet.
Before Getting Started
Use standard commercial potting mix based on peat moss (it’s sterile and free of pathogens). Although the oaks will eventually be planted in garden soil, potting mix is the safest way to start healthy seedlings.
All acorns should be planted in the fall as soon as possible after you collected them. White oak and swamp oak will germinate soon after planting. For bur oak, pin oak, and red oak, you won’t see germination until the next spring because these oak species need stratification, which you’ll provide by leaving the pots outdoors during the winter.
Equipment / Tools
- Small trowel
- Soilless potting mix
- Small pots or seedling pots
Select Viable Acorns
Fill a bowl with cold water and place the acorns in it. Viable acorns will sink or remain at the bottom while damaged or empty ones will float. Discard the floating acorns. Briefly soaking the acorns also helps rehydrating them if you stored them before planting.
Plant the Acorns
To plant the acorns, use pots deep enough for root growth. 2.5 x. 2.5 x 3.5-inch pots are ideal. Fill the pots with potting mix. Place two acorns sideways in each pot, at a depth about three times the width of the acorn, or about 1 inch. Water them well until water runs out of the drainage holes.
Keep Soil Moist
Keep the soil moist until the onset of winter weather. (During winter, you can leave them be. In the spring, restart watering them.) Keep the seedlings weed-free. Both the acorns and young seedlings need to be protected from getting eaten. After planting the acorns, cover the pots with a screen or hardware cloth. Once the seedlings emerge, lift up the protection as needed to give the seedlings room to grow.
Thin the Seedlings
Regardless of when the acorns germinate—in fall or spring—if both acorns in a pot germinate, cut off the weaker of the two seedlings about one to two weeks after the seedling emerges. Do not pull out the second, unwanted seedling because its root system will be entangled with the roots of the oak you want.
Transplant into Larger Pots
When the seedlings are about 5 to 6 inches tall, or when the root system starts to reach the side of the container, transplant the seedlings to 2-quart nursery pots with large drain holes. Fill the pots with a mixture of half potting soil and half garden soil and add 1 teaspoon of a slow-release fertilizer to the soil.
Relocate to Permanent Spot
Once the roots are growing out of the drain holes, the saplings have a good root system and it’s time to plant them in their permanent location. Dig a hole about three times the diameter of the container and the same depth. Add organic matter if needed to improve drainage. Water the saplings and spread a thick layer of mulch in a 2-foot perimeter around the base but leave at least a 2-inch space between the mulch and the tree trunk. Tender oak saplings are favorite food for browsing deer and other wildlife. Make sure to protect the tree with a mesh tree guard for at least three years.
Can I plant an already sprouted acorn?
Yes, you can. Place it sideway in the soil with the primary root (radicle) downwards, and be careful not to break the root tip.
Are acorns planted point up or down?
Neither, acorns are planted sideways. The primary root will emerge from the pointy end and grow downwards.
Can I start an oak tree from acorns inside?
Acorns that do not need cold stratification can be started inside but once the seedling starts growing, it should be moved outdoors.