A green acorn is the seed of an oak tree, but planting one is highly unlikely to result in a new tree. Successful germination depends on the acorn completing a complex maturation process while still attached to the parent tree. Planting an acorn requires it to be fully developed, correctly prepared, and placed in conditions that mimic its natural environment. Successful growth begins with selecting a mature acorn that has finished drawing the necessary resources from the parent tree.
Why Green Acorns Are Not Ready
A green acorn is still actively connected to and drawing resources from the oak tree. The transition from green to a rich brown or tan color signals the completion of its physiological preparation for independent life. Until this color change occurs, the acorn has not fully provisioned itself with the massive energy reserves required for germination. These reserves, stored as complex carbohydrates, fats, and proteins, must be at their peak concentration to sustain the seedling until it can photosynthesize.
The immature seed has not yet developed the necessary desiccation tolerance for survival once it is separated from the tree. Acorns are classified as recalcitrant seeds, meaning they cannot survive being dried out completely, but they must still achieve a specific moisture content to be viable. The final maturation phase involves complex changes that allow the seed to tolerate the natural moisture loss that occurs after falling. Planting a green acorn essentially forces an abortion, as it lacks the stored energy and chemical signals to initiate the germination sequence.
How to Select Mature Acorns
Identifying a mature acorn relies on visual cues and a simple water test. A viable acorn will have changed color from green to an even shade of brown or tan, depending on the species, indicating its growth cycle is complete. The cap should also detach easily from the nut without tearing the shell, which signals full ripeness. Inspect the surface for signs of damage, such as pinholes indicating acorn weevil larvae, or any soft spots or mold.
The most reliable way to check for internal viability is the float test. After removing the caps, place the acorns in a bucket of water and allow them to soak for a short time. Acorns that are dense, full, and healthy will sink to the bottom because they have intact internal material. Conversely, acorns that float are likely hollow, dried out, damaged by insects, or otherwise non-viable. Discarding the floaters increases the chances of successful germination.
Preparing and Planting for Success
Once you have selected viable, sinking acorns, the next step is often to break their natural dormancy through stratification. Many oak species, particularly those in the red oak group, require a period of cold and moist conditions to mimic winter before they will germinate. This requirement can be met by placing the acorns in a sealed container with a damp medium, such as peat moss, sand, or shredded paper. The container should be stored in a refrigerator at temperatures between 32 and 41 degrees Fahrenheit for 30 to 60 days.
Planting Procedure
Some species, like white oaks, often germinate immediately upon falling and can be planted directly without stratification. When planting, the acorn should be placed shallowly in the soil, usually buried about one to two inches deep. The orientation does not need to be precise, as the emerging root, the radicle, will naturally grow downward. Choose a location or container with well-draining soil and consider protecting the planting site with a screen or wire mesh. This barrier helps prevent squirrels and other wildlife from consuming the newly planted seed before it has a chance to sprout.