In honor of the Arnold Arboretum of Harvard University celebrating 150 years in 2022, we offer our longest-standing members the gift of our most historic trees—seeds drawn from the oldest dawn redwoods (Metasequoia glyptostroboides) in North America. Thought to be extinct for millions of years, dawn redwood seeds were collected by Hu Xiansu and Hwa Ching-Tsan in Hubei, China and sent to the Arnold Arboretum in 1948. The Arboretum distributed seed to 600 other botanical institutions throughout the world, and now we present you with seeds from our iconic sentinels. We invite you to cultivate these living fossils.
Upon Receipt of the Seed
Keep the seed in the envelope at room temperature or place in your refrigerator. Either option is fine until you are ready to sow the seed in late winter.
How to Sow Dawn Redwood Seed
Q. What do I do first with the seed in? A. Divide the seed in the envelope into two groups in late February or early March. Group 1 will be sown outdoors. Group 2 will be placed in the included small bag of potting soil for prechilling.
Q. Do I need to divide the seed into two groups? A. No. But, by trying two different after-ripening treatments you may have overall greater germination.
Q. It looks like there is other debris mixed in with the seed. What is it? A. Seed was cleaned, meaning all that was not seed was removed. However, a few needles may still remain. There is also red resin from the cones.
Group 1: Sow Directly Outside
Q. When and how should I sow Group 1 seed outside? A. Sprinkle seeds outdoors into garden soil in late February or early March. Top dress the seed with a very light layer of soil. Seed should be buried no deeper than 5 mm. If there is snow, remove the snow from the top of the soil and plant seed if the ground is not frozen.
Q. Why do I sow Group 1 seed outside when it is still cold? A. Dawn redwood seed requires a cold period, like many temperate tree and shrub species. Providing a dormancy-breaking treatment will promote higher germination of your seed in spring.
Q. What do I do when Group 1 seed germinates in spring? A. Note your results on the included record card. Consider transplanting or thinning if a large number of seedlings germinated in a small area.
Group 2: Stratify in Potting Soil
Q. What do I do with Group 2 seeds? A. Place the seed in the included small bag of potting soil and mix in. Lightly mist the soil and seed mixture with water from a spray bottle. The soil should be moist, but not wet. Place the bag in your refrigerator for 30 days. This process is called stratification, which is a cold, moist period that mimics winter. Fresh seed will germinate without a cold treatment, but 30 days of chilling unifies germination.
After 30 days in the refrigerator is over, sow the seeds in a small container filled with potting soil at a depth of 5 mm. Place in a warm, sunny spot indoors. Water when the soil is dry to the touch and visually appears lighter in color. Your container should have drainage holes.
Q. What do I do when Group 2 seedlings germinate? A. Note your results on the included record card. Gently transplant seedlings into containers filled with potting soil and keep indoors until temperatures warm up in May. Transition your plants outdoors. Keep your containerized plants in the shade, as they are used to being indoors and not receiving full sun. After the plants have rooted into their containers, transplant into your garden.
Aftercare
Q. I have small dawn redwood plants in my garden. Now what? A. Congratulations – you now have offspring from the oldest North American dawn redwoods in your very own garden! Ensure your plants have at least 1 inch of water either from rainfall or from supplemental irrigation during the growing season. Consider mulching, which will mitigate weed competition and also help to retain soil moisture. Make sure that the base of the plant is not buried by mulch. Consider protection from animals if the plants are being browsed.
Q. My seed did not germinate. What’s wrong? A. Seed was collected from two mature specimens in the Arnold Arboretum’s living collections in late fall 2021. Seed is open pollinated and viability was not evaluated. We unfortunately cannot ensure germination.