The winter solstice is past, and each day the sunlight coming in my windows is a little bit stronger and lasts a little bit longer. While the cold and snow outside tell me winter is still keeping a firm grip on my Vermont garden, these gradually lengthening days hold out the promise of spring weather ahead. They tell me that, in spite of snowstorms and below-zero nights, gardening season is on its way and it’s time to think about starting seeds indoors.
Although January is too early for me to actually begin planting seeds indoors in my climate, it’s a good time to start planning which seeds to start and ordering them online or purchasing packets at my local garden store. (For help figuring out what to start when in your climate, see When to Plant Seeds.) It’s also the time to check that all my seed-starting supplies are ready, from fluorescent grow lights to germinating mix to cleaned and sanitized pots recycled from previous seasons. (To get re-used containers ready, I scrub them in warm, soapy water; rinse them; then soak them in a tub filled with 9 parts water and 1 part household bleach for 15 minutes. Next I rinse them with clear water and let them air dry.)
All seeds are in a state of suspended animation, waiting for the right set of conditions to awaken and begin to sprout. For many kinds of seeds, warmth and moisture will rouse them into growth. But for some kinds of seeds, germination requirements are more complex. Some seeds contain chemical and physical inhibitors that keep them from germinating when the environment isn’t suitable. Once the seed receives the proper conditioning that destroys these inhibitors, it “knows” that it’s safe to start on the journey to becoming a plant. Understanding what conditioning particular seeds need sets you on the path to starting these seeds successfully.
Some seeds have a very hard seed coat that in nature is broken in a variety of ways that assure that the seed germinates under the proper conditions. Alternate freezing and thawing temperatures, extreme heat from a fire, passing through the digestive system of an animal are all ways in which a hard seed coat can be breached to allow moisture in. We can reproduce this conditioning with a procedure called scarification, which is simply nicking, scraping or cutting through the seed coat. For example, you can cut off the pointed end of a morning glory seed with a sharp razor blade or scrape the seeds across a piece of sand paper. If you have a lot of seeds to scarify, put them in a jar with some coarse sand and shake vigorously.
Sometimes soaking is enough to soften the seed coat to speed germination. Soaking can also speed germination by removing chemical inhibitors from the seed coat. Soak parsley seeds for 24 to 48 hours before planting, pouring off the water and replacing it with fresh several times, discarding the leached out inhibitors in the process.
When we think of planting seeds, what springs to mind is usually a picture of tucking seeds into the soil. And while some seeds do need the darkness of a soil covering for germination, most will germinate in light or dark, though the covering of soil helps to keep them moist. But some do require exposure to light to break down inhibitors in the seed coat. Lobelia, impatiens, and ageratum are flower seeds that need light for germination; simply press them on to the surface of the germinating medium, rather than burying them.
Certain seeds, usually of perennials, trees, and shrubs from cold-winter climates, need to be exposed to a certain duration of cool temperatures before they’re ready to germinate. This chilling requirement prevents them from sprouting prematurely when the weather is too cold for growth. In nature, these conditions are provided by normal seasonal changes. When gardeners mimic this process, it’s called stratification. Seeds are given a period of moist cold (40-45 degrees F) for about 6 weeks to duplicate going through a cold winter; a refrigerator easily provides the appropriate “winter” chill.
Once seeds have been conditioned, most need warmth in addition to moisture to germinate well. The majority of the seeds we start early indoors appreciate bottom heat from a seedling heat mat or the top the refrigerator that keeps the germinating mix between 70 to 80 degrees F.
How to know what’s best for sprouting various kinds of seeds? Check the instructions on the seed packet for the specific requirements of the seeds you’re starting. Happy planting!