Introduction to seed stratification

Perennials are those flowers we look forward to returning in our gardens every year. Whether colorful Irises or the bold Peony, they’re a favorite among gardeners. These flowers seem to magically appear during spring reminding us of the colorful spot they filled the previous year. Long before this reawakening occurs, the seeds have been prepared for growth by the natural cycle of seasons.

Seeds in Nature
Seed germination begins once the conditions for its growth are favorable. This means that a seed can lay dormant until necessary, a neat built in feature for gardeners that pre order their favorite blooms.

Seeds are essentially a case holding the plant embryo. In nature, the seeds absorb moisture through soil causing their outer coat to break. This starts a chain of chemical reactions that allows the plants cells to duplicate and it to begin growing. The root is the first to emerge from its tiny plant cocoon and begins its search for nutrients by growing downward into the soil. This tiny root also serves as an anchor for the seed and a home base for all the oxygen, nutrients, and sunlight that the seed will need to continue its growth.

Once the process begins, the seed needs only three things to survive; water, oxygen, and correct temperature. Mother Nature provides all of these of course, and since the requirements are so necessary at the correct time, gardeners have learned to nurture seeds through the process.

Seeds that germinate in cold winter areas however, have an additional requirement before they will emerge. These hearty seeds ensure survival by developing hardened shells. The shells are softened by the fall rains before being exposed to the low temperatures of winter. It’s not until this two-step process occurs that the seed germination process begins. This process, seed stratification, is how the seeds are signaled to awaken and grow.

What is Seed Stratification?
The term seed stratification can sound intimidating to gardeners, but it’s simply a term used to describe the pretreatment to begin the seed germination process. Think of it as a “jump start” to the rush to spring growth. Other terms you may encounter while reading up on the topic are “cold stratification” or “warm stratification.”

This pretreatment process simulates the conditions that occur in nature and allow us to control when the seeds begin to germinate. Stratification coaxes the seeds embryos from their dormant state and can take months. Since the balance is a delicate one, in nature plants develop a multitude of seeds. Many of them will never reach the maturity for germination and even more end up as bird food or meet another fate.

When gardeners intervene, the process of seed stratification can take over three months. This makes planning ahead essential. Further increasing the need for garden planning is the fact that every species of seed has their own likes/dislikes when it comes to the germination conditions. Some are of course more stubborn than others are and this can be especially true of the seeds of trees and shrubs.

Seed Stratification: The Need
Seeds that grow in the regions that have especially cold winters have greater requirements to coax them from their safe cocoon.  Unlike other growing conditions, these seeds are not happy with simply being placed in good soil with a little light and water. These seeds need an extra boost to get them to open up; this boost is the seed stratification process. Gardeners can intervene by introducing the seeds to the type of conditions they would naturally be found in nature. The seeds from the cold winter areas are built to be especially hearty; they are to endure colder temperatures and so developed a tougher shell. This shell is what seed stratification seeks to break through, to jump start the seed germination process and bring the sleeping flower back to life.

Again, keep in mind that the goal with seed stratification is basically faking winter conditions to prepare a seed to sprout.

The Stratification Process
We know that seed stratification is a way to simulate the conditions that a seed needs to begin germinating. Essentially the goal is to simulate the seasons of fall and winter, then the seed knows that spring is here and nature takes over.

Generally the ideal temperatures for warm stratification are 68 to 86 degrees and cold are 34 to 41 degrees.

Simulating fall starts by soaking the seeds for a period of 24 hours. This is commonly done by placing seeds in a shallow container with water. A small jar is then used to place seeds in water for soaking in cold temperature. This simulates the cold temperature of winter and its end, imagine it as the snow melting.  The seeds are then removed and placed in soil once the required time for seed stratification is met (will vary by seed species.)

Another method referred to as the “paper towel method” is also popular for seed germination. You will need a medium to hold in the moisture, a growing medium such as sand, sphagnum moss, vermiculite, or peat moss. The two requirements are that it has to be sterile and retain moisture. You’ll first soak the seeds overnight to simulate the fall season, then lay them on a moistened paper towel that has been wrung out. Seal the seeds in by folding the paper towel in half and applying pressure. Place the paper towel in a plastic bag and into the fridge they go for an average period of three months, simulating winter. It’s good to check the seeds once a week once you are past the first month to ensure that they are starting to germinate. Any seeds that smell musty or have brown spots should be disposed of, these will not be making it to the year’s garden patch .Another fast method to jump start the seed stratification process is to use the refrigerator for placing seeds in jiffy pots. These are just kept cool for a short period of time to get the process started.

You can tell by now that a certain amount of planning is necessary to be successful with seed stratification. It starts not only with the species that you wish to germinate but also with the time that you would like it to grow. The process will vary depending on fall, winter, or even snow planting.

Though the variety of techniques for seed stratification can seem endless, the basics are the same. The goal is to simulate the fall and winter seasons, softening the seed before exposing it to cold temperatures to start germination. Undoubtedly, one method will work for a certain species and fail with another, keeping a gardener’s journal will help you to nail down which works best for your favorite seeds.

As a note, some seeds require both a warm and a cold stratification period for them to germinate. In these cases, the warm seed stratification process is done first followed by the cold. It should also be noted that this is the general outline of a seed stratification process. Each plant and growing region has specific requirements and may respond very differently to conditional variances. Specialized information should be obtained for each type of perennial, tree, or shrub seed you wish to germinate.