The seeds of some flowers and vegetables, such as morning glory, moonflower, beans, and certain perennials, need a little extra treatment before they will germinate.
There are special germination instructions on the back of our seed packets that explain how they are done. Don't worry! These extra steps are easier than you may think.
Scarification
Seeds with a hard, almost impenetrable seed coat ("testa") need some help breaching the seed coat to allow the seed to absorb ("imbibe") water so it can germinate. In nature, these seeds would go through a process of freezing and thawing that would naturally break this seed coat. Here are a few easy ways to mimic the natural process (with most seeds you can choose any one of these three):
Roll seeds over sandpaper or a file. Once you see a color change in the seed coat, they are ready; you don't want to damage the inside of the seed. You can also line a container (film canister or tin can) with sandpaper and shake the seeds inside the container for about one minute.
Nick the seed coat with a nail clipper or knife on the opposite end of the area that looks like an "eye spot" (or the pointed end in some cases), which is where the first root ("radicle") will emerge, always being careful not to damage any tissue inside of the seed.
Soak seeds in tepid water for 12 to 24 hours (but not longer; seeds need air too).
Scarification should be done just before sowing, since this treatment leaves seeds vulnerable to decay.
Stratification
Stratification is a cold, moist period that breaks seed dormancy. In nature this process occurs in winter, keeping seeds from germinating until conditions are more ideal in the spring. Perennials (plants that live for several years) are more likely to require stratification.
You can promote natural stratification by sowing in the fall for spring germination. You may experience a little seed loss due to critters, but because this is an easy method, most gardeners feel it is worth it.
Stratify using your refrigerator:
Sow seeds into a sanitized container of moistened seed-starting mix, following instructions on the packet for seed depth.
Cover the container with plastic wrap.
Place the container in the refrigerator for 3 to 8 weeks, checking moisture regularly. Refer to the seed packet for the ideal number of weeks to stratify.
Remove the container and place in a warm (some packets list an ideal temperature range) indoor area, leaving the plastic wrap in place until seeds have germinated. Refer to the seed packet for any special light or darkness requirements for best germination. Keep seeds and seedlings moist.
By Dan Heims, President, Terra Nova Nurseries, Inc.
Photographs courtesy of Terra Nova Nurseries, Inc.
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