There are many ways we can start afresh in 2021. In the plant world, rebirth isn’t visible until spring, yet the time for preparing and sprouting often happens unseen, when everything seems the most quiet and dead.
Winter is a great time to start propagating your favorite native plants, and this article will discuss some of the best winter seed propagation techniques in case you’d like to try at home, or to begin fathoming the intricate natural system of native plants.
This article will discuss the natural, magical, and mystical winter seed germination (sprouting) and the types of dormancy native seeds use to protect their future.
Perennial plants fall into several broad categories: smaller forbs and vines whose growth dies back in the cold, and sturdier shrubs and trees, who live long lives and spend years establishing themselves. Winter seed treatment is helpful for these woodier shrub and tree species, that put a little more effort into hedging their seed germination bets. If you were a big, beautiful shrub, and wanted to give your seeds the best chance for survival, you wouldn’t want them to germinate immediately and all at the same time. You would want your seeds to wait, to lay dormant until the perfect time, and maybe even be transported by animal digestion and time.
Seed dormancy is often two layered. There are seeds that have physical dormancy, and those that are physiologically dormant. Physical dormancy means the seed coat is hard and prevents water and air access to the seed interior preventing germination. These seeds are meant to stay in the wild for years and, over time, through various natural occurrences, their seed coat will break down and they will germinate.
To speed up this process in the nursery, various scarification methods are used. An easy method is sandpapering the seed coat, but this can take time and is labor intensive for each seed. An easier method used by propagation enthusiasts is pouring boiling water on seeds and leaving them overnight. Depending on the species this can take a few tries to break down the coat, but when the seed seems swollen as though it has imbibed the water, you’ll know you’re ready. Species that appreciate this type of seed scarification are most things in the Fabaceae (legume) plant family (mesquite, senna, Dalea, Tecoma etc.).
Another method used is fermentation. Many seeds that are fleshy (think berries) need fermentation to elicit germination. Often this means you can just leave the berries to soak in water with their pulp for about a week before the seed coat is activated and they’ll germinate. Species that appreciate fermentation are berry plants like the Rhus (sumac), and Ribes (currant).
Physiological dormancy is an internal dormancy (not seed coat related) where factors inside the seed tell it when to germinate. For many shrubs of our mid- and high-elevation mountain regions, the seeds are counting down the cold moist days, waiting for winter to pass before they germinate.
Ways to speed up the process is to cold stratify the seeds; in other words, trick the seeds into thinking that winter has come and gone. What plant mother would want their seed babies to germinate in October or November, right before a long cold period? They’d rather wait until the cold has passed and they know the elements are warm enough to support them.
The best trick to break cold physiological dormancy is to find a sterile water-supporting medium (sterile sand, peat moss, or coconut husk work well), wet it so it’s spongy, not drenched in water, and tuck the seeds into the media. You can then put this in a plastic ziplock bag and put it in your fridge. Make sure to mark the bag and your calendar. You don’t want to forget and snack on them later. Once enough time has passed, you can plant the seeds in a pot or in the ground, and with water and warmth, they’re ready to go.
One month is an average time to cool the seed. At the Borderlands Restoration Network seed lab, they’ve written down the ideal fridge times for a number of native shrub species and should be able to help you determine how long to store the seeds in the cold.
You can email horticulture@borderlandsrestoration.org if you have any propagation questions, or join the local Santa Cruz chapter of the Arizona Native Plant Society at Santacruz.aznps@gmail.com to get together with other native plant nerds and discuss propagation.
Happy new year! The plants are excited too.