Wild native seeds are tricky to germinate!
It comes as no surprise to native plant gardeners that wild native seeds do not behave the way that cultivated crop seeds do. Humans have bred cultivated seeds from wild relatives of crops over a very long time. They have evolved to have predictable behavior and consistent germination in response to conditions manufactured by humans, such as in an agricultural field with a set watering schedule. Seeds of wild native plants, on the other hand, are finicky! Why? Not only are there more variables that affect the viability of wild-collected seed, but they often have complicated dormancy.
What is seed dormancy?
All seeds need three things to germinate: water, light, and an optimal soil temperature. The exact amount of each depends on the species and the ecosystems in which they evolved. However, seeds of many wild native plant species have developed different dormancy mechanisms that keep seeds from germinating even if you give them a nice pot of soil, ample irrigation, and sunshine. Seed dormancy refers to mechanisms that inhibit germination when conditions do not support a seedling’s survival and growth or trigger germination at the onset of favorable conditions.
Dormancy can prevent germination physically through the development of impermeable barriers or hormonally, which often means that a change in temperature or pH in the seed environment is required to turn on or off the hormone that maintains dormancy or stimulates germination.
Breaking dormancy and germinating seeds in nature is a slow process that can take months or even years. You can always apply seeds in your garden without any treatment, ideally, in combination with rain-water collecting basins and mulch, provide water, and they should germinate eventually. However, this may take time, and germination may be staggered.
What are dormancy-breaking seed treatments?
Dormancy-breaking seed treatments are things that growers do to the seeds to mimic the natural biological process of dormancy breaking and to speed up the process to encourage germination within a shorter time, usually a couple of weeks to a couple of months. The most common treatments Borderlands Nursery & Seed uses are:
Warm Water Soak: The most common inhibitor to seed germination is simply the presence of ABA or Abscisic acid. A simple overnight soak in room temperature water can help cleanse the seed of this hormone and jump-start water absorption to encourage germination. We like to soak most of our seeds before sowing.
Scarification: The process of mechanically wearing down the seed coat, so it is permeable. This treatment helps overcome physical dormancy, in which the seed has developed a hard, impermeable coat. Scarification is done with sandpaper, garden snips, a scalpel, pouring boiling water over the seed, or even using a bench grinder. Be careful to puncture only a corner of the seed not to damage the embryo!
Tips: The boiling water pour-over treatment is excellent when repeated 2-3 times for hard bean seeds like Mesquite or Senna. For even harder beans, like Coralbean (Erythrina flabelliformis), mechanical scarification with a bench grinder, followed by a hot water pour-over left to soak overnight, works very well.
Cold Stratification: Place seeds in a moist, but not saturated, soil media in a plastic sandwich bag and leave it in the fridge for 30, 60, or 90 days. This treatment helps to overcome physiological dormancy, which requires an overwintering period of consistently cold temperatures followed by warm temperatures that signal to the seed that winter is over, and it is safe to germinate without seedlings dying in a freeze event. Make a note on the bag or a notification on your phone to remind you to take the seeds out and sow them when the cold stratification is finished.
Tips: This is an excellent treatment for cool-season spring bloomers like Penstemon species, Thistle (Cirsium) species, or mid-elevation woody shrubs like Apache Plume (Fallugia paradoxa), Cliffrose (Purshia stansburyana), or Desert False Indigo Bush (Amorpha fruticosa). It is also effective for most tree species, except for the riparian gallery forest species like Cottonwood, Willow, or Arizona Sycamore, which only need to be direct sowed without treatment and watered well. An even longer cold stratification of 60 - 90 days can be helpful for very high-elevation species, such as Arbutus arizonica.
Acid Scarification: Soaking seeds in warm water and lemon juice overnight or fermenting seeds with fleshy fruits in water for a week. This treatment can help to overcome physiological dormancy by exposing the seeds to acids that change the pH and can turn off germination-inhibiting hormones. This treatment can also help to overcome physical dormancy by weakening the barrier around the seed.
Tips: The warm lemon water treatment works very well to open seeds with difficult to penetrate papery casings, like Desert Kidneywood (Eysenhardtia orthocarpa), and works well for seeds of the Chiltepin pepper. A short fermentation can have a similar effect for seeds with fleshy fruits that are tasty to wildlife and often germinate after fermenting in their sugars on the forest floor or passing through the gut of a bird or mammal. To ferment seeds, place seeds with fleshy fruit in water for a week or two before sowing or putting into a cold stratification. Add sugar for seeds that have been dried and removed from their fruits.
Warm Stratification: Leaving seeds on a heat mat or in a warm place for a period of time to overcome morphological dormancy, which is when seeds are dispersed before the embryo is fully developed. They need an “after-ripening” period of warm temperatures to develop and mature. Species with morphological dormancy often germinate better when the seed is older and has been sitting around for longer.
Some seeds don’t need any treatment!
Annual species tend to germinate more readily with enough moisture and warmth and don’t usually need a complicated seed treatment. This is true for some of our favorite annual species, including Mexican Golden Poppy (Eschscholtzia californica var mexicana), San Pedro Matchweed (Xanthocephalum gymnospermoides), Common Sunflower (Helianthus annuus), Lemon Beebalm (Monarda citriodora), and Yerba Porosa (Porophyllum ruderale), and short-lived perennials like Evening Primrose (Oenothera elata). Also, in southern Arizona, most milkweed species, grass species, Agave species, and aster or sunflower species can be directly sown and watered well without additional treatment. Many species with little tiny seeds, such as Coralbells (Heuchera sanguinea), can be sown without any treatment and should be surface sown and then patted down with only a tiny bit of soil on top so that the light can still penetrate through to the seeds.
What to do if you think your seed is dormant but you can't figure out what type of dormancy or how to break it?
First, google it! You may not find information about how to germinate the exact species, but often tips on germinating other species in the same genus is an excellent place to start. Next, try trialing different dormancy-breaking treatments to see which treatment results in the highest germination rates. We are constantly learning, and the only way to gain horticultural knowledge is by repeatedly trying, observing, and adjusting based on what you learn.
Never hesitate to contact us with questions about germinating or growing native plants! Email horticulture@borderlandsrestoration.org. We love to hear from you and will always give the best advice we can. We enjoy hearing about your successes and seeing photos of your gardens!