Stratification is a process that seeds naturally complete involving a period of colder temperatures before a warm period suitable for germination and growth. This process mimics the conditions that the seed would have been exposed to if it had been left on the ground, a cool season before the growing season. There are three common methods involved in breaking seed dormancy; stratification, scarification, and light, all of which are used together.

Every plant needs to be treated individually when it comes to stratification requirements. It is hard to generalize groups of plants. Many native shrubs and some trees need longer periods of stratification, some need up to two years. Specific stratification needs are addressed on the Species Summary Sheets.

To gain controlled and consistent results, generally, grass seeds should be cold/dry stratified for a few months prior to planting. Prairie wildflowers often require a period of exposure to moisture and cold; most native plants stratify themselves naturally by seeding out in late summer or fall. During the stratification processes, natural inhibitors that prevent early seed germination are leached out of the seeds and/or are broken down.

For cold/moist stratification, soak the seeds for 12 - 24 hours and then mix the seeds with damp sand or peat moss (wet the material and then wring it out). Place about an equal amount of seed to planting medium in a labelled plastic bag. Store the bag in a refrigerator (at 2- 4 ºC) for a minimum of 4 to 8 weeks prior to sowing. Check the bag occasionally for germination or fungus growth. If germination occurs plant the seeds immediately. If fungus growth occurs remove the sand/seed mixture from the bag and allow it to dry completely. Apply a small amount of a horticultural fungicide or a diluted bleach (Javex) solution, then re-moisten the mixture and replace in the refrigerator.

During the storage period for a cold/dry stratification, the seeds are susceptible to consumption by insects and mice. The seeds should be stored by hanging them in feed bags somewhere that they will remain consistently cool. If this is in a barn or shed, be sure to keep the sacks out of the reach of mice and possibly mix in some food-grade pesticides (e.g. diatomaceous earth) to deter insects.

Natural stratification can also be encouraged by sowing the seeds in an outdoor location to overwinter, after the temperature is consistently below that needed for germination (after November 1rst, usually).

Scarification is the intentional damaging or removal of the seed coat. This is a process needed for seeds with a tough outer shells or skins. In nature this is usually accomplished when the seeds pass through the digestive system of an animal. In the classroom scarification can be done as the physical abrasion of the seed coat which leads to enhanced moisture penetration and promotes germination in seeds. Gently rubbing seeds between sheets of medium grit sandpaper. It is also popular to shake them in a container lined with a medium sandpaper or filled with a gravel/sand mixture to accomplish the scarification. Some seeds respond better to a chemical scarification, and these are then immersed in sulphuric acid for a few minutes. None of the plants discussed here need an acid treatment, few, if any will need the sandpaper treatment. As with stratification, different seeds have different needs which are outlined on the species specific information sheets.

Some seeds require light in order to germinate. Do not cover these seeds with soil after sowing. If grown indoors or in a greenhouse setting, they should be watered from the bottom, by way of placing the plug tray into a shallow tray filled with water. If grown outdoors a layer of burlap (which will allow some light to penetrate) can be placed over the seeds to help maintain the soil moisture. In either case the soil should be kept moist.

Seed success rates are also dependent on many other factors such as seed handling and storage, as well as the physical factors affecting the planting. Even after a successful stratification period, seeds will not become 100 percent successful when sprouting.