How to Help Seeds Break Dormancy
by Jeanne Wilson
Many California native plants have evolved special “triggers” to help them germinate at the best time and in the optimum conditions to
promote their growth — when moisture, temperature, light, and/or soil chemistry are at or above the threshold for success. Fortunately, horticulturists have figured out ways we can mimic such natural conditions.
Seed coat dormancy treatments include hot water or dry heat treatment (even fire); cold stratification; scarification (scraping or breaking the seed coat); and treating seeds with acid or other chemicals, charred wood, or mulch. Some species may have multiple types of dormancy and may require a year or more to be ready to germinate. Most are much less complex. In general, fresh seed is not dormant and does not require special treatment.
Luckily, not all species need special seed treatment, and most of our local natives need fairly simple treatments. Three of the simplest are hot water treatment, cold stratification, and scarification.
Hot Water Treatment
For hot water treatment, generally heat water almost to boiling; then pour it over the seeds in a cup or other waterproof container. Leave the seeds in the water for 24 hours. Then either plant or cold stratify for several weeks or months. Seeds needing this treatment include lupines, wild peas, and other members of the pea/bean family (Fabaceae) – many of these also need cold stratification.
To cold stratify seeds, wrap them in a damp paper towel and put into a plastic zip bag. Label each bag with species, date stratification started, and recommended end date of stratification. A good source of information about how long seeds of particular species need to be stratified is Dara Emery’s book, Seed Propagation of Native California Plants. A bag can hold several seed species, as long as you label each wrapped group of seeds. Store the bags in your refrigerator.
After several weeks, check stratifying seeds regularly for radicles — the first root. Pot up any seeds that have radicles, covering the seeds with a thin, light layer of vermiculite or potting soil.
Seeds of spice bush (Calycanthus occidentale) on paper towel, just sprouting radicles
Breaking external or “seed coat” dormancy of seeds with hard outer coats involves scarification. This scarification may be done by scraping (such as with sandpaper), penetrating (creating a hole in the cover), softening, or otherwise breaking the outer protective surface. Sometimes only scarification is needed, and the seed can be planted without further treatment, other times scarification is combined with additional treatment.
For more information about these and other seed treatments, including how and when to use them, see the Resources list on our Propagation page, and check Dara Emery’s book Seed Propagation of Native California Plants, published by Santa Barbara Botanical Garden, available as a free download on Calscape. Print copies available via Amazon.