How to Winter Sow Seeds Outdoors By Jerry Berry, MG 2008 Winter sowing is a method of starting seeds outdoors in winter. This is generally done with seeds that require a period of cold and moist stratification. The method takes advantage of natural temperatures, rather than artificially refrigerating seeds. Winter sowing involves sowing seeds in a miniature greenhouse outside during winter, allowing them to germinate in spring. Stratification is a pre-germination technique designed to break the dormancy in seed and to promote rapid, uniform germination. Seed dormancy is a condition of plant seeds that can prevent germination unless certain environmental conditions are present. One important function of most seeds is delayed germination, which allows time for dispersal and prevents germination of all the seeds at same time. The staggering of germination safeguards some seeds and seedlings from suffering damage or death from short periods of bad weather or from transient herbivores; it also allows some seeds to germinate when competition from other plants for light and water might be less intense. Winter sowing helps to break seed dormancy through exposure to moist cold temperatures. Most perennial flower seeds require cold and moist conditions before they will germinate. What you’ll need: Soilless Seeding Medium This is very important as soilless mediums are sterile and can prevent diseases like “damping off” (a fungus that will kill seeds and seedlings). Below are soilless starting mediums you can make. 2 parts Peat Moss 1 part Perlite (provides aeration) OR 2 parts Peat Moss 1 part Vermiculite (holds moisture) OR You can go to a big box store or a local garden nursery and get a seed starting mix. Do not use potting soil or dirt (soil) from your yard. 1 Containers Ideally, pick a container with a clear top. Recycle any trays or containers you might have at home, or go to a dollar store and buy some. You can use just about any container, and if you don’t have a lid, just place it in a clear baggie. Punch or drill holes in the bottom of each container for proper drainage. Punch a few small holes in the tops and sides of each container for proper air circulation and transpiration (without air circulation, you can literally “cook and kill” your seeds and/or seedlings on a warm and bright sunny day). Fill the container with your soil medium to about two inches from the top. Water well and let it drain. The soil medium should not be so moist that you can squeeze water out of a handful. After the container has drained, sow your seeds and pat them down or cover them, whichever is required. Since you have “pre-moistened” the seeding medium, there is no need to water after you have planted the seeds. Be sure and label each container with some sort of weatherproof label (something that won’t wash off or fade in the elements). Now just take it outside to somewhere it will be safe for the winter. Away from pets etc. Just let Mother Nature do her work. Over the winter, your containers will freeze, and thaw, and then freeze again, etc. This action of freezing and thawing helps loosen the seed coat and breaks seed dormancy. From time to time, especially on an above freezing day, check the moisture content in your containers, and if need be, add a little water. Actually, some rain or melting snow will fall through the tiny openings in the lid, so this step may not be necessary. It won’t hurt to check every so often though. When winter is about to break, and you’re still getting nightly freezes, the first of your containers will begin to germinate. Don’t worry. The seeds know when it’s safe to come up; it’s part of their genetics. When the seedlings have their first set of true leaves (the first leaves are not true leaves), you can feed them with a liquid fertilizer, but only at about 5% strength. You can increase the strength of the fertilizer as the weeks continue and your seedlings become more robust. Seeds Seed packets will usually list stratification/ scarification requirements and there are many books and resources available, where seed requirements can be found. The internet is an excellent resource. Most seed catalogs will have some sort of information about a seed’s germination requirements. For example, Park’s Seed Catalog has an excellent reference section on the number of days it takes seeds germinate. Look for these terms: Needs 2 pre-chilling, freeze seeds, refrigerate seeds, stratify for x amount of days or weeks, needs scarification, etc. Some seeds need darkness to germinate (cover with soil) and some seeds need light to germinate (do not cover with soil). The requirements for sowing depth can usually be found on the individual seed packets. Try not to crowd your seeds in each container as they will have too much competition from other seeds and will be more difficult to “thin out” after they have germinated (about ¼” apart is a good rule of thumb). With small seeds this can be a tedious task, but it’s important to give them the correct spacing. When can I start? Winter Sowing is done during the winter, but if you start too soon there’s the concern of a late season warm spell that will stimulate some seeds to germinate prematurely. Take a look outside. When the leaves have all fallen off the trees, we are probably into winter, and you can start. Starting around Thanksgiving is probably OK as well. Winter Sowing Glossary Dormant seed: Alive but inactive, and in some cases, incapable of growth until certain conditions have been fulfilled (light, moisture, temperature). Perlite: Volcanic rock that has been heated to expand. Perlite is used in soil mixes to provide aeration. Scarification: The practice of scratching or notching the seed coat so that moisture can more easily penetrate the seed coat. Stratification: Moist chilling of the seeds to break dormancy and promote germination. Many seeds need 30 to 90 days of this treatment. Transpiration: The evaporation of internal water from plant leaves. 3 Vermiculite: A form of heat expanded mica used in soil mixes to retain moisture. Vernalization: The seeds ability to germinate, and then flower in the spring, following prolonged exposure to winter elements. Reference material: The New Seed Starters Handbook by Nancy Bubel Growing and Propagating Wild Flowers by Harry R. Phillips The Plant Propagators Bible by Miranda Smith Photo Credits: Indiana Public Media Earth Eats, and the author’s own photo collection. 4