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Native Perennial Seed Stratification

Sustainable Marblehead member and Tower School science teacher Colleen Parenteau and her sixth-grade students met at the Tower School with members of Marblehead’s Winter Garden Club to do an in-person training on how to harvest, store, stratify and sow native plant seeds in pots.

The seeds were harvested by the students and members of the Sustainable Marblehead Conservation Group’s Pollinator Corridor team from the native plant project at Glover Landing last year.

At the training session, Tower School students made the following presentation on native perennial seed stratification – the process of giving seeds a period of “cold” to prepare them for better germination. (If you don’t stratify seeds, they can still germinate, but the rate is often much lower and they can actually take two or three times longer to germinate.)

Why should we conserve wild-type native plants?

  • Many commercial nurseries favor cultivars and hybrids bred for desired traits.

  • Hybrids and cultivars lack genetic diversity and reproductive ability to adapt.

  • Native plants can adapt to changing environmental conditions.

  • Native plants attract native pollinators.

“Over 80% of the flowering plants on earth depend upon insect-mediated pollination, and wild bees are twice as effective as honeybees in producing seeds and food crops, as well as assisting trees, shrubs, forbs and vines in reproduction.” ~ Evan Abramson, Pollination Systems Designer,

How to germinate native seeds

  • You don’t need expensive or sophisticated facilities.

  • Native seeds should germinate outdoors in beds or pots.

  • Germination outdoors is often better than when seeds are sown in a greenhouse. Greenhouses can be too hot and humid, resulting in rot.

  • Outdoor seeds germinate when the conditions are right for each species. For some, that’s in the frosty temperatures of early spring and others in the heat of summer.

  • Seed flats or plastic pots work well: 4”-10” in diameter, 3” + deep.

  • Place pots in a shady spot away from foot traffic.

  • Share seed species with your friends.

Sowing seeds

Steps to sowing native seeds:

  • First put damp soil into the pot.

  • Then, put the seeds on the top, seeds can be planted close together, sow the seeds to the depth of the thickness of the seed and roughly 1/8 to ¼ inch apart.

  • Label with the name and sowing date.

  • Put coarse sand over the seeds and soil (to keep the seeds from blowing/splashing away).

  • Place outside (seeds must be cold and wet to break open the seed coat).

  • Keep watered, every few days to once a week.

  • Finally put a screen over the pots so that animals do not eat the seeds.

Waiting for germination

  • Different species of seeds take different amounts of time to germinate. Cultivated plants and veggies can germinate more rapidly because they have bred specifically to do so. However, some native seeds may take a week and some may take months, or years after sowing!

  • If a plant does not germinate, it will most likely germinate the following year. DON’T THROW THEM OUT IF THEY HAVE NOT GERMINATED, BE PATIENT!!

  • If you sow seed that needs a cold period and it’s too late in spring, you can cover them with plastic and put them in the refrigerator for 60 days (this is called artificial indoor cool stratification).

Transplanting seedlings into larger pots

  • Most native seeds can stay in their original pot for the first season.

  • If you think that the seeds are crowded, you can divide them into different pots and beds.

  • In the process of transplanting the seeds, bunch 3-10 seeds in each pot unless it’s a tree species. This certifies that the new seeds that grow will have genetic diversity.

  • A thinned LIQUID seaweed fertilizer once a week will promote growth and help keep plants healthy. Tower School uses Neptune’s Harvest Seaweed fertilizer.

Overwintering seeds and protection

  • You need to protect your seeds when germinating them over the winter from severe weather and windburn. Many layers of winter grade Reemay cloth and white plastic on top of that will work well to protect your plants from harsh winters.

  • Your plants should be frozen before this process, so mice and other rodents won’t consider your plant bed as a hibernation spot. You can also try covering plants with salt marsh hay to reduce the use of plastic materials.

Learning by Doing

We have had the most success with growing native plants by doing the following:

  • Using high quality compost ~ “Fort-Vee” from Vermont Compost Company.

  • Using pots and flats with good drainage.

  • Placing pots in the right sun conditions.

  • Transplanting year-one pots into a raised bed or year-two pots into the ground surrounded by wood chips or mulch to keep weeds at bay.

  • Saving seed each year from healthy plants.

  • Learning from experts.


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