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Tuesday, July 2, 2013

The Germinator

As you may know, a number of the plants on the Berry Prairie were grown from seed, specifically for use on the green roof.  Starting wildflowers from seed can be as easy as throwing them on the soil.  More often, however, it takes careful and strategic processes that range from refrigeration to scratching to freezing to burning.  The post below gives an overview of the many ways we germinate seeds, including as it relates to Jenna's Indian Paintbrush project.


Seed Germination

Not every seed will grow as soon as it is in the ground. Seed dormancy is the failure of a viable seed to germinate under adequate environmental conditions; a seed will germinate after dormancy is overcome or broken. Seed dormancy is desired in the wild because plants depend on nature for survival. If a seed germinates but the conditions are not right for growth the seedling will die. Some seeds require stratification while others require scarification.

Penstemin eriantherus blooming on the Berry Prairie.

Scarification is where the seed coat is scratched to loosen the covering. The seed will not germinate until the seed coat is altered physically, to make it permeable to water. This happens in different ways in nature. One way is by a seed falling, or being scratched on a rough surface. Another example of scarification can occur is when it passes through the digestive tract of various animals. Strawberries and raspberries are an example. Frugivores, like bears, digest the fruit pulp, but the seed coat passes through the digestive system and the acid in the digestive track breaks down the seed coat making it ready for germination.

Castilleja chromosa seed just starting to germinate
after 2 months in the fridge.
Stratification is when a seed undergoes a cold or hot treatment to break dormancy. This happens in nature when it snows in the winter. Many of our native wildflowers require stratification. For example, when Karen Panter started Penstemon eriantherus for the Berry Prairie, she kept the moist seeds in the refrigerator for up to three months before planting! Seeds can be put in moist soil or perlite, or even just in plastic bag with a bit of water, before refrigeration. We used this last technique to germinate Indian paintbrush seeds—read more about that soon.

Another way to stratify seeds is to plant them during the late autumn or winter, and leave the pots outside over winter. Some plants will germinate even better the second year, after overwintering twice.

The fires that occurred this summer and last in Colorado have created a lot of destruction. Even though it does not seem like it, the fires have also created growth. The heat of the fire actually weakens the covering of some kinds of seeds enough to enable it to intake moisture and germinate. This is common for pinecones; they are tightly shut and the heat allows them to open and release the seeds.

The wildflower Corydalis aurea is common after wildfires.
Fire stimulates its long-lived seeds to germinate.

Written by Jenna Ramunno, Biodiversity Institute

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