Stratification is the process necessary for seeds to break dormancy prior to germination. Many seeds with physiological or physical dormancy need to go through proper temperature treatment before they can be put in conditions favorable for germination. By doing so we fool the seeds into thinking that they have gone through a winter and are all set to sprout.
For “deeply dormant” seeds such as juniper, both warm and cold periods are needed to induce germination. For seeds requiring both phases, the warm phase is done first to soften the seed coats and allow the embryo to mature.
For species with hard and almost impenetrable seed coats, scarification is sometimes needed to weaken, soften or breach the seat coat to induce germination. This can be most easily done by soaking seeds in either warm to hot lukewarm water or 1% to 15% hydrogen peroxide solution for at least 24 hours. In some cases, boiling water is required to break down the seed coats.
Because water imbibition is a critical first step in seed germination, it is important to soften or break down the seed coats allowing water entry. There are several ways to break down hard seed coats: 1) pouring hot water over seed and soaking for up to 24 hours; 2) mechanical methods such as files or abrasive tools to physically score the seed to allow water entry; 3) chemical seed coat degradation using concentrated acids (sulfuric).
Different seeds are divided into different categories depending on the degree of dormancy and the pre-sowing treatment method.
Seeds with light or no dormancy
Seeds with embryo dormancy
Seeds with deep dormancy