Fall brings the opportunity to collect ripe acorns, the fruit of the oak tree, for science classroom activities or home-based science projects. Botanically, the acorn is a nut containing a single seed encased in a tough leathery shell. Acorns of the northern red oak, Quercus rubra, the most common oak species in central Maine, provide fodder for studies of seed dormancy and germination.

Students can collect acorns, test them for viability by flotation, and study stratification and germination. Many excellent science fair projects have sprouted from classroom activities involving acorns.

Collecting acorns

Acorns of northern red oak take two years to mature. They are best collected as soon as they fall from the tree (early September in central Maine), since acorns left on the ground for any length of time will be eaten by animals or infested with disease. In fact, only one in 500 acorns survives to become an oak seedling. No wonder oak trees produce so many acorns!

Second-year acorns are brown and often detached from their cap; first-year acorns that have dropped prematurely are green and typically remain capped. Although the first-year nuts will not germinate, you may want to let the students collect them and discover this for themselves. Also, acorns with small holes drilled by weevils or other insects are not likely to grow.

The proportion of viable seed can be increased by removing defective, hollow or partially consumed acorns. This is done by simple flotation. Place the collected acorns in a bucket of water and discard the ones that float.

Stratification and germination

Stratification is the process of pretreating seeds to simulate natural conditions that must occur before germination is possible. Ripened red oak seeds contain a dormant embryo that must be exposed to winter’s cold before germination is possible. This ensures that the seedling will not emerge until spring when conditions favor growth.

Stratifying acorns involves refrigeration between 32 and 40 degrees F for 30 to 90 days. During this time the acorns should be stored in plastic bags containing a moist mixture of sand or sand and peat. Be sure to keep the bags sealed to prevent loss of moisture. Use only new materials to avoid infecting the acorns with fungus disease.

After 30 days the acorns should be inspected every few days to detect root emergence, considered the first visible sign of germination. At each inspection, the total number of germinated seeds can be recorded. At 90 days, it can be assumed that all acorns capable of germinating have done so. (Although red oak acorns will germinate – show root emergence – after as little as 30 days of chilling, shoot growth will not occur until after a much longer period of chilling.)

Several aspects of stratification can be investigated. Teachers can help their students develop hypotheses from essential questions. Does acorn size or color affect seed viability or germination rate? Does stratification temperature affect percent germination? How does percent germination vary with stratification time? Does flotation of collected acorns remove only the nonviable seeds? Does presoaking the seeds in water improve percent germination?

Experiments then can be conducted to test these hypotheses, dividing the collected acorns into treatment groups, each with 10 to 50 acorns, depending on the number collected. Teachers can modify the experimental design, data collection and data analysis for different grade levels.