Seed starting is a widespread indoor gardening activity this time of year. It can be a great way to satisfy your gardening desires while waiting for spring to happen, but not all seeds are the same in their startup requirements. If you’ve ever tried to start seeds from native plants, you’ve likely been met with a bit of surprise or even disappointment when the vibrant seedlings you expected did not emerge.
Nature's Built-in Winter Protection
Most, but not all, native perennials have seed stratification requirements, meaning there are steps you need to take to pre-treat the seeds to ensure germination. This can be especially puzzling for many when you think about the masses of plants out in nature that easily grow from seed each year. There is nothing special done to those seeds, yet I have columbine (Aquilegia canadensis) popping up all over my gardens each spring, and there are tons of rattlesnake master (Eryngium yuccifolium) seedlings under my mature plants each year.
This all goes back to that age-old dilemma for gardeners in which we try to make plants do the things we want in our garden spaces, but they just don't always seem to pay attention. While it can be very frustrating to plant seeds and see little or no return, this is also the stuff that makes gardening fun. It wouldn’t be such a rewarding pastime if there weren’t some kind of challenge, right?
I’ve found it fascinating to test and observe the results of cold stratification. To me, all of this is simply a science experiment with varying factors we can manipulate to get the intended results. So, it helps to understand the basic biology behind the process before attempting any experiment.
How to Stratify Seeds Yourself
Essentially, seed stratification practices are designed to mimic natural conditions in winter. In most cases, simple cold stratification is required for a period of 30-60 days. This can be accomplished in a controlled environment, such as a refrigerator, or as simply as storing seeds in an unheated garden shed or outdoors over our colder months.
This mechanism has evolved in nature to prevent germination at the wrong time of year. When my rattlesnake plants drop their mature seeds in fall, it is critical that germination is delayed because the tender new seedlings would certainly be killed by frost and the consistent cold during winter months. With a built-in thermometer of sorts, the rattlesnake master seeds are programmed to await cold exposure before they sprout, which perfectly times the emergence of new seedlings with warmer spring weather.
Along with the exposure to cold, many seeds also require moisture to ensure good germination later. This is certainly a requirement in a refrigerator or other artificial settings because seeds can dry out, killing the embryo inside. In nature, our winters are filled with moisture, and seeds laying at or near the soil surface are constantly exposed to rain, sleet, snow, and other naturally occurring moisture.
However, natural conditions are not always perfect for stratification, and that’s why plants typically produce lots of seeds. Much of the seed production is expected to fail and that’s okay in nature when there is a thriving population of plants. The smaller fraction that succeeds in growing will be enough to perpetuate the species.
However, when you plant a flat of seeds expecting 100 seedlings to emerge, it's not ok to have 20% germination. So, we need to take extra steps with native seed to be sure maximum germination is achieved and to make our efforts worthwhile. In essence, we need to create the perfect winter conditions, which stay below 40 degrees for the required cold period while seed moisture is consistently maintained.
Additional Seed Dormancy Tricks
Some seeds have additional requirements beyond cold, moist stratification, and this is where things get interesting. Another part of the natural process of seed dormancy and germination is the breakdown of the seed coat or the protective outer layers of a seed. This protective layer naturally breaks down over time in nature, but we often need to give it some help in cultivation.
The process of breaking down the seed coat is referred to as scarification. It can be accomplished in a variety of ways, from knicking with a knife or rubbing it with abrasive materials, like sandpaper, to exposing the seed to boiling hot water.
If you’ve struggled with this in the past, perhaps the best recommendation is to leave it all to nature. Any seeds that require cold stratification work wonderfully when directly seeded in the fall and left to Mother Nature over winter. In spring, you should be pleasantly surprised with a bed of thriving seedlings.
Photo Caption: This seed pod contains up to 200 native milkweed seeds that require exposure to cold conditions, called cold stratification, before germinating.