Warm-moist stratification
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seeds moistened (between paper towel or planted in moist soil) at 20°C or higher for 30 to 90 days
*Seeds often germinate during this period, but they may not fully emerge, continue with pre-treatment protocols for your species to ensure the seedling will fully emerge.​
Warm-moist stratification is often used along with cool-moist stratification for species with morpho-physiological dormancy. These seeds have underdeveloped embryos at maturity (Baskin and Baskin 1998). In order for these seeds to germinate, embryo growth must occur and physiological dormancy must be broken.
For some species, it is important which occurs first: i.e. embryo growth or breaking physiological dormancy. These seeds are often referred to as "two year" seeds, because they require two winters and one summer before germinating in the spring. We emulate these conditions by exposing seed to cool-moist stratification as above and then to warm-moist stratification which requires a temperature increase to approximately 20°C or higher and then repeating the process of cool stratification.
This process is species specific and the protocols can be found in the species profiles. Often a seed will germinate during warm stratification, but it is important to continue with pre-treatments as described to ensure the seedling fully emerges. If a seed has fully emerged (showing both the root and first leaves) it can be carefully transplanted to soil medium.
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Seeds from native plants often must be treated before they can be planted, or they may not grow. This is especially true for orthodox seed that exhibits many types of seed dormancy.
Seed dormancies inhibit germination to protect the seed from growing during unfavourable conditions. For example, in northern Ontario if seeds fell from the plant in the late fall and grew immediately, it is most likely the seedling would die from the harsh winter conditions. Instead the seed is dormant when shed from the plant and the cool-moist conditions on the soil surface send a signal to seed. Once warm spring temperatures arrive, the seed will be ready to germinate.
There are seven types of seed dormancy described by Baskin and Baskin (1998). They include physiological, morpho-physiological, and physical seed dormancies. The most common pre-treatment recommendations to overcome these dormancies includes: cool-stratification, warm-stratification, scarification,chemical leaching, and a combination of these methods. Pre-treatment protocols are perhaps the most diverse and species specific of all protocols.
Several species are also considered non-dormant which means they can be planted without pre-treatment.
Growing native seed
Cool-moist stratification
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Place seeds between moistened paper towel in a breathable container. Keep in the refrigerator or a place between 1 to 5°C.
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OR plant seeds in moistened soil, keep cool, such as under the snow pack during winter.
* Seed should be checked periodically to ensure the paper towel is moist and that mould has not developed.
Some species that are non-dormant may still benefit from some period spent in cool- moist conditions if they are collected from northern climates (Baskin and Baskin 1998).
Many seeds with a physiological dormancy can be treated with cool-moist stratification.
Moistened seeds are placed in temperatures of 1 to 5°C for a period of 30 to over 120 days depending on the depth of the dormancy. This emulates the winter that seeds would endure under natural conditions, before growing in the spring. ​
Leaching germination inhibitors
The last pre-treatment protocol we describe on this website is the leaching of germination inhibitors, such as in silverberry seeds (Fung 1984).
Chemical compounds within the seed sometimes stop it from germinating. If the compounds are water-soluble, they may be soaked in warm water to remove germination inhibitors.
Seed coat scarification
Some species require scarification of the seed coat so water can reach and be taken up by the embryo, called imbibition (Baskin and Baskin 1998). Scarification is commonly required for legumes and species that are animal dispersed, including many of the berry producing shrubs.
There are many methods for overcoming physical dormancy listed in Baskin and Baskin (1998).
Two common methods are. scarification using chemicals such as 50% to 98 % sulphuric acid or physically by damaging the seed coat, such as rubbing seeds between sandpaper, or shaking seeds in a container with rocks or other abrasive materials.
Pre-treating native seed
Germination of seed
After your seeds have been pre-treated, they can be planted and grown. Typical germination conditions are:
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Seeds kept moist (not soaked)
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potting soil, sand, etc
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Temperatures: 15 to 25°C (usually 12 hours cooler and 12 hours warmer.
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Light and dark cycles: Dark-12 hours, light-12 hours.
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Moisture must be adequate for the germination of all species. Some species, such as junipers, require cooler temperatures to germinate (Tylkowski 2009). Labrador tea and mountain cranberry germinate best at higher temperatures, approximately 30°C and need a lower soil pH in order to germinate (Karlin and Bliss 1983, Royal Botanic Gardens Kew 2016). Some species are mycorrhizal and may require inoculation with fungal spores to thrive, or they may be parasitic and rely on other species for nutrients, shortly after their seeds have germinated. For instance, Indian paint brushes will lose vigor if host plants are not introduced shortly after they begin to grow (Luna 2005).
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Literature cited
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Baskin, J., and C. Baskin. 1998. Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination. Academic Press, San Diego, CA.
Fung, M. Y. P. 1984. Silverberry seed pretreatment and germination techniques. Tree Planters’ Notes 35:32–33.
Karlin, E., and L. C. Bliss. 1983. germination ecology of Ledum groenlandicum and Ledum palustre spp. decumbens. Arctic and Alpine Research 15:397–404.
Luna, T. 2005. Propogation protocol for Indian paintbrush (Castilleja species). Native Plants 6:62-68.
Royal Botanic Gardens Kew. 2016. Seed information database. http://data.kew.org/sid/
Tylkowski, T. 2009. Improving seed germination and seedling emergence in the Juniperus communis. Dendrobiology 61:47–53.
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Sectioned northern meadowrue seeds.
Prickly wild rose seed germinating.
Red raspberry seeds soaking in sulphuric acid.
Silverberry seed soaking in hot water.
False star Solomon's seal germinating on potting soil and vermiculite mix.