Stratification is the process that some seed require in order for them to germinate successfuly. Many seeds will enter a state of dormancy, which is where the seeds wont sprout even if they have access to enough water and light. The seeds enter dormancy as a means of allowing them to wait for specific environmental condition, such as cold weather or change in temperature, before they germinate.
If those environmental conditions isnt provided to the seeds, the seeds may not germinate at all. One of the methods of stratification is known as cold stratification. Cold stratification is the process of placing the seeds into a moist medium and then placing the entire package into a refrigerator.
How to Cold Stratify Seeds
Many fruit trees, such as apple and cherry trees, require cold stratification for periods of two to three month. If the gardener do not perform cold stratification on these types of plants, their germination rate will be low. However, by performing cold stratification on these types of plants, their germination rates will increase as a result of the process.
The process of cold stratification requires that the pulp can lead to mold growth on the seeds, as the gardener first cleans each seed of any attached pulp. Following the cleaning of the seeds, the seeds should be soak in water for overnight. Following soaking, the seeds should be mixed with damp peat or sand.
The medium should be damp enough to clump when held in the hand, yet not wet enough that the medium will drip when held in the hand. Following mixing with the medium, the seeds should be place into a bag for storage and labeled with the date of storage. The bag containing the stratified seeds should be placed into the refrigerator, but not near fruits.
Fruits release gas into the air that can cause the seeds to sprout premature. During the stratification process, the seeds should be checked each week to ensure they did not dry out or become too wet during the period. Some seeds have hard coat, which prevents water from being able to reach the seeds.
To assist in the germination of these seeds, the process of scarification is used. Scarification is the process of breaking the seed coat by rubbing the seeds with sandpaper or nicking the seed coat with a file. When using a file, care must be taken to ensure that the embryo inside of the seed isnt damaged.
Another method of scarification is to pour near-boiling water over the seeds, which allow the seeds to soak as the water cools. Some seeds, such as redbud seeds, require both scarification and cold stratification. If these types of seeds are scarified and undergo cold stratification, the success rate of those seeds will increase.
Certain types of seeds are what are known as double-dormant seeds. Double-dormant seeds require two phase of dormancy to be broken. Examples of double-dormant seeds include trillium and bloodroot seeds.
These types of seeds require a warm and moist phase to occur for a period of many month, after which a cold phase occurs. Because the process to germinate double-dormant seeds takes place over a long period of time, often over a year, the seeds require extended storage. In order to germinate successful, each type of seed requires a specific method to be performed.
For instance, many native perennials and shrubs require cold stratification to germinate. However, tropical plant species, such as tomato or basil plants, wont require cold stratification to germinate, as they germinate well in warm temperatures. Grass seeds require shorter periods of cold stratification than fruit trees.
To determine the type of cold stratification that is required of a given seed, the origin and coat of the seed should be observed. The germination viability of the seeds can be test by soaking the seeds in water; seeds that float will not germinate. There are some mistakes that can be made in the stratification process.
For instance, if the gardener places the seeds into a freezer rather than into a refrigerator, the cells in the seeds will be frozen and the seeds will die. If the medium into which the seeds are placed is too wet, mold can grow on the seeds. If the bag into which the seeds are placed are not labeled, the seeds can be difficult to find and manage.
Additionally, if the bags are stored near fruits, the ethylene gas released by the fruits will cause the seeds to sprout premature. Additionally, if there is too much cold provided to the seeds during stratification, the seeds may sprout while still within their bag. To avoid these issues, the seeds should be routinely checked during the stratification process.
Additionally, cold stratification should of been started at least ten week prior to the last frost date in the season. One alternative process is known as winter sowing, wherein the seeds are planted in soil within milk jugs, which are then place directly into the snow. Through winter sowing, the seeds are provided with cold stratification without the effort of the gardener.