Botanist's Lens: Seed Dormancy: "Surviving the Adverse"
Seed germination is one of the most critical points in the life cycle of a plant. Seeds vary in size, structure, texture and a whole lot more. Seeds are an evolved critical dispersal unit for higher plants. The time from when the seed is formed till it germinates is very critical and involves many growth phases as well as dormancy stages.
"Many garden plants have seeds that will germinate readily as soon as they have water and are warm enough, though their wild ancestors had dormancy. These cultivated plants lack seed dormancy because of generations of selective pressure by plant breeders and gardeners that grew and kept plants that lacked dormancy." Source: https://en.wikipedia.org/wiki/Seed_dormancy
Dormancy is simply preventing untimely germination. Viable seeds that have longer dormancy periods are able to survive many adverse conditions, can be dispersed at longer distance, and can usually germinate under favorable conditions. But when these seeds belong to an invasive shrub, that is not helpful for any habitat. For eg. in an invasive species like 'Cytisus scoparius', its long seed dormancy is not beneficial to its neighboring habitats. The seeds can stay dormant for 50 years!
Dormancy levels vary by species. Plant propagators however have many tricks to surpass dormancy and initiate germination sooner. A few of those dormancy breaking techniques that our plant propagation group is using include:
Stratification: some seeds need a period of warm or cold temperatures before it can germination. Cold stratification is when the seeds can be exposed to cold temperatures and then brought out in warm temperatures to speed fast germination. We are using a regular freezer to store seeds in cold temperatures and then bringing them out in warm temperatures. Seeds are stored in peat moss/directly in soil but are covered in air tight bags to prevent moisture leak.
Scarification: some seeds have a very hard seed coat. These could use manual scarification; removal of part of seed coat to enable moisture to penetrate and act as a catalyst to lead to germination (see picture of Peony seeds)
Light treatment: some thin seeds can germinate faster when exposed to light for a certain duration. For eg., Azalea seeds could use 16-24 hours of direct cool white fluorescent light, at least 8 inches above, to fasten germination.
Moisture treatment: this is the easiest for seeds with a harder seed coat. The thicker the seed coat, the longer you could soak them to loosen the seed coat. Hot water shock for couple of hours/days of soaking in water can fasten water imbibition to start germination. Featured are pictures of the plant propagation group working hard in the greenhouse as well as some water treatment and scarification effects on seeds.
Seeds are fascinating! Did you know that some seeds need fire, smoke, or the right animal dispersal agents to start the catalytic activity and germinate? Dormancy varies in type and duration. After all, dormancy is a plant's way to try harder to create better chances for its offspring to survive, ride out adverse conditions, and also keep a bank ready in the soil, in case of bad weather. Dormancy can act as good back up plan!