Certain environmental factors – water, temperature, oxygen, and light – must be favorable before seeds can germinate. That means that the seeds are dormant because certain mechanisms delay germination until the seedlings have the greatest chance of survival. If germination took place in the fall, the seedling would be killed because of the cold temperatures or lack of moisture. Dormant seeds are more common in wild plants than cultivated species. In nature, dormancy is overcome by a combination of time and exposure to the elements. Rainfall, chilling, alternate freezing and thawing, and attack by microorganisms are just a few examples.
Choose one type of seed or a variety. Plant some of the seeds in a container filled with potting soil. For the other, first moisten the sphagnum peat moss with warm water and drain off the excess. Fill several plastic bags with a handful of the damp moss. Add the seeds. Use a separate bag for each different type of tree seed. Label them 1 month, 2 months, 3 months and the date you started this project. Place the bags where the temperature will be between 35 and 45°F. A refrigerator should be within the proper temperature range. Avoid freezing temperatures, because they may injure the seeds. Occasionally check the bags to see if the medium needs re-moistening.
Find out the minimum length of chilling needed for the trees that you chose. At the end of one month remove the corresponding bag and plant the seeds. Be sure to label it. A the end of two months, remove the ‘2 month’ bag and plant the seeds. Do the same after three months. Which ones needed the least amount of chilling? The most?
Another treatment to overcome seed dormancy is scarification. This is any process that breaks, scratches, mechanically alters, or softens the seed coat and makes it more permeable to water and gases. Some common methods include water, acid, or mechanical. Some trees that have seeds with tough seed coats include honeylocust, Kentucky coffeetree, American yellowwood, and locust. Their seed coats are impermeable to water unless the coat has been partially eroded away. In nature, this happens after several months of exposure to the weather. You can scarify (scratch or cut) the coat with a metal file until you see a small white hole in the coat. Plant some seeds that have been scarified and others that have not. Compare how they germinate.