If you’re having trouble getting some of your seeds to germinate, it may be that you’re being too nice to them. Armed with tough defenses against all that nature can throw at them, some seeds refuse to grow unless they’re forced to. This year, consider seed assault and battery, followed by water torture. Here’s how to abuse your seeds.
The coat of some seeds is very hard and tough. Normally, this protects the seed and ensures that conditions for germination are favorable. In nature, seeds may pass through the digestive tract of a bird or animal, or be burned in a fire. A hard seed coat gives these seeds a longer storage life as well.
Since you’re unlikely to eat or roast your seeds, you need to provide another way for air and water to reach the tiny embryo inside that armored seed coat. Using chemical or mechanical means to create a weak spot or crack in the seed coat is called “scarification.”
Since chemical scarification is usually done using rather strong acids in a very controlled setting, we’ll focus on mechanical scarification.
Some seeds are shipped from the grower already mechanically scarified. (Be sure to plant these right away as they won’t store very long.) Geranium seeds frequently come pre-scarified.
To scarify large seeds, you can use a knife, rasp or file to saw a niche in the seed coat. This allows water and air to penetrate. Be careful not to injure the embryonic plant inside. Then soak the seed for 12 – 24 hours before planting. Smaller seeds may be too difficult to handle; just soak these.
Examples of seeds benefiting from scarification include apple, beans, beets, canna, carrots, celery, honey locust, impatiens, laburnum, lupine, mimosa, morning glory, pansy, parsley, peas, stone fruits, and sweet peas.
Some seeds come with a chemical inhibitor to keep them from germinating under inhospitable conditions. Others need prolonged soaking to absorb water through their mostly-impermeable seed coat, as mentioned under “scarification.”
Soak seeds by placing them in a labeled container and pouring hot (not boiling) water over them. Use about 6 times as much volume of water as seed, to allow for absorption. Soak the seed for 12 – 24 hours; then plant immediately. Once wet, never allow them to dry out, or the embryonic plant inside will die.
Not every seed should be soaked first. Some become too fragile when saturated. Beans absorb the water too quickly, which damages the seed. Examples of seeds benefiting from soaking include okra, asparagus, parsley, lupines, sweet peas, morning glories and many trees and houseplants.