Breaking Dormancy in Seeds and Bulbs
Breaking dormancy for cold-hardy seeds and bulbs requires mimicking plant germination cycles, techniques called stratification, which is accomplished by controlling temperature and moisture for a period of time. Stratification has been in practice for hundreds of years and was first described in the 1664 writings of English Horticulturist John Evelyn. Evelyn’s emphasis on the relevance of stratification had to do with efficiently growing trees to replenish timber for British Navy ships. In botanical terms, stratification is distinguished from “chilling” which is the amount of cold time fruiting plants require to blossom, also known as vernalization. Although it sounds complicated stratification is easy to do when you are equipped with the right information for each of your plant choices.
It’s important to understand that there are two types of dormancy both endo-dormancy and ecto-dormancy. Endo-dormancy is before chilling whereas in ecto-dormancy chilling has already occurred and the plant is ready to begin growing once the temperature rises sufficiently. “As the plant enters endo-dormancy, it tracks chilling units to track the passage of the winter. Chilling units are hours of time spent above freezing,” according to Michigan State University. “As long as the plants are in endo-dormancy they have the ability to acclimate to colder temperatures and withstand winter cold. After chilling is completed the plants are no longer in endo-dormancy. They are now in eco-dormancy. The plants are dormant only because of cold or cool weather. Warmer temperatures into the mid-40s will cause them to begin growth. Once the plants start to grow, they lose the ability to readjust to colder temperatures. There is usually a slow progression of development when the plant begins to grow as the temperatures slowly rise.”
Most Northeast Florida native and tropical plants germinate in warmth, but the cold-hardy varieties with thick seed coatings often require a set period of cold temperature and moisture to soften the shell and break dormancy. “Having such a tough shell ensures that germination occurs only when conditions are right,” according to The Guardian. “Weather fluctuates; you don’t want your seed jumping into germination just because autumn has a few cold nights and then a warm one. It’s not spring yet and those cold nights did not represent winter. So time and temperature are the keys necessary to unlock germination for many seeds.”
Considering breaking dormancy requirements are specific for each species follow the seed and bulb package stratification recommendations for time, temperature, and planting media. Additionally, if chilling in the refrigerator is deemed appropriate, ensure that the temperature, packaging material, and germination media are also appropriate. Stratification in the refrigerator is typically better done in paper than plastic, which improves air circulation and reduces threats from pathogens. While some plants germinate best wrapped in a damp paper towel in the back of the refrigerator others do just fine in a pot of soil outside. Do your research.
Seeds that require cold stratification include Anise Hyssop, Asparagus, Milkweed, Baby’s breath, Black-eyed Susan, Butterfly bush, Caper, Chinese Lanterns, Columbine, Coneflower, Delphinium, Echinacea, Geranium, Lavender, Lobelia, Oregano, Poppies, St. Johns Wort, Sunflower, Violet, and Yarrow. Although Earth Works typically offers seedlings of many of these varieties of plants when they produce seeds stratification is required for germination.
Tulips grown from bulbs in Florida require cold stratification to break dormancy, as do daffodils and hyacinths. “To grow tulips successfully, the bulbs need cold treatment, but not moist stratification or storage in a damp soil medium,” according to SFGATE.com. “Although tulips prefer a moist planting site, the bulbs are mainly responding to the cold temperatures rather than water availability.” A few of the bulbs that don’t require chilling for Florida gardens include Anemone, Allium, Caladium, Crinum lily, Gladiolus, Oxalis, and Turks Cap.
By learning to mimick plant germination cycles successfully and breaking dormancy techniques you will significantly increase the varieties of plants you can successfully grow and enjoy year after year in your lawn and garden.
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