This article by Dorothy Swift originally appeared in WildfloraRI, Spring 2018.
Why grow wild plants from seed?
Growing plants from seed provides more plants for your property than buying larger, more costly plants from a commercial or nonprofit source. Certainly, either Lobelia cardinalis or Penstemon digitalis is lovely as a single plant, but most people want multiple cardinal flowers or groups of penstemon throughout a planted area.
When you grow plants from seed, you may be able to obtain seed of local origin for a species. Using locally-sourced seed is a sound ecological approach for establishing wild plants on your property and for including species that are not readily available commercially or are prohibitively expensive.
Finally, there is the challenge of doing something that might be difficult and the satisfaction of acquiring knowledge and experience in the propagation of native plants.
For a home gardener, how might this be different from growing vegetables and flowers from commercial seeds? Generally, commercially available vegetable and flower seeds germinate readily, whether you sow them in the ground, start them earlier under artificial lights, or use natural light from a window. Many of these plants are annuals or are tender perennials treated as annuals horticulturally. Only a few native species respond with immediate germination, as popular commercial vegetable and flower garden seeds do.
Most native species require a cold period before the seed will germinate. This is often referred to as “cold stratification,” a technique that exposes seeds to moist, cold conditions for a period of time. (The seeds must be in a moist medium, such as a seed-growing mix. Dry storage of seed in the refrigerator does not meet the need for cold, moist stratification.) A few species have even stricter requirements, such as a warm period followed by a cold period followed by a warm period. It can take up to a year or longer for some seeds to germinate. You must be prepared for a longer investment of time and nurturing when growing most native species from seeds.
How do you learn the best method for starting a native species from seed? There are several ready sources. For 30 years, every WildfloraRI issue has had a Cultivation Note which includes information about the best habitat for a species, how to propagate and grow the plant, and in most cases, how to grow the species from seed.
Our favorite source of advice in Seed Starters East is Willam Cullina’s book, Growing and Propagating Wildflowers. Cullina worked in the propagation and nursery operation at New England Wild Flower Society for many years and writes about his personal experience propagating numerous native species. He explains their requirements for germination and provides advice on techniques to save time with some of the slower species. Though out of print, used copies of Cullina’s book are available from online services, such as Alibris.
Doing an online search can also be useful. Use the species name and “seed propagation” to find information, particularly from various other native plant and conservation organizations. Your results will include a lot of sources, but for most species the first two listed are adequate.
If you have difficulty finding information on a species, you may want to use the work of Norman C. Deno, Seed Germination Theory and Practice, 2nd edition. Deno’s work concentrates entirely on germination, not on how to grow plants further. His presentation of information can be a bit difficult to understand, but the work encompasses hundreds of plant species. The entire work can be found online.
What are some of the basics of wild plants from seed?
1. After you collect and clean or purchase seed, refrigerate it if you are not going to sow it right away. I put envelopes of dried seed on a shelf of my refrigerator door for storage. Alternatively, put seed into small bottles or vials, together with a desiccant. (You can save the little packets of desiccants from commercial products, such as large bottles of pills). Do not store seed at room temperature
2. When you are starting out, use a seed starting mix rather than a general potting mix. Some plants germinate readily and grow vigorously, so potting mix can be suitable, but in general, a fine-textured mix formulated for starting seed works best. I use a mix from Gardener’s Supply Company. It is expensive but is free of weed seeds and contaminating microorganisms. Published instructions for some plants, such as lily species, may recommend milled sphagnum moss, which is also very finely textured. Alternatively, you can purchase sphagnum moss and rub it through a fine sieve or between your fingers to get fine particles. Also, carefully clean any used pots or containers to avoid bringing fungus pests to your seed-starting. You can run your pots or seed boxes through a dishwasher to remove disease organisms.
3. Carefully moisten the seed-starting mix. This is more critical for seed-starting than for transplanting. Proper wetting of the mix may require less water than you might think is correct. Moist, but not too much, is the key. To control moistening more easily, prepare a small volume of mix at a time. Then fill the seed-starting container, and settle the mix by rapping it against a hard surface.
4. Learn whether the seed should be covered or uncovered by the seeding mix. Several kinds of seeds, such as Lobelia cardinalis and Rhododendron species are small and need light, so spread them onto the surface of the mix. Avoid sowing the seeds heavily. You do not want the baby plants coming up like a lawn. For seeds that need to be covered, the depth should be approximately the diameter of the seed. Label the container with the species name and the date. Mist the container with water.
5. Maintain moisture after sowing. Enclose the seed container in a Ziploc bag or a takeout food container with a tight semi-transparent cover, especially if seeds are indoors under lights. If you rely on window lighting, never place the container of sown seed where direct sun shines on it. Check periodically that the container is still moist, and mist if necessary.
Many seeds, as mentioned, need a cold period after sowing. Put the container into your refrigerator or outdoors with protection from rodents. Outside, place plastic-covered containers under shrubs for shade, or cover larger seed flats with rigid metal hardware cloth or screening. Alternatively, you can use a cold place, such as an enclosed unheated breezeway, the stairs of a bulkhead entrance to a basement, or a cold frame. Light is not required during this cold period.
6. When germination begins, remove any plastic covering, and keep the mix moist by using a mist bottle or by setting the container in water so that moisture is absorbed from the bottom. If you must water from above, use a small watering can with a small-diameter spout that can dispense water very gently.
7. Do not transplant seedlings until they have a pair of true leaves, which emerge after the cotyledons or seed leaves. When transplanting, hold a seedling by a leaf to prevent damage to the stem. Seedlings don’t do well with too much space, so transplant several into a pot, or plant seedlings in rows in a takeout food container.
These suggestions should help you get started in growing native plants. Seed Starters East has sold seeds of several species this year. We selected ones that are likely to succeed if you follow simple directions. For species that need no special treatment, try Lobelia cardinalis, Penstemon digitalis, and Aquilegia canadensis. The milkweed species, Asclepias tuberosa and Asclepias incarnata are easy species but need a cold period.