Seeds with hard outer coats surrounding them (like nasturtium, shown) can be hindered in their ability to germinate because moisture and gases cannot penetrate through the coating. So what do you do? You scarify them.
Seed scarification helps weaken the hard coat surrounding the seeds in order to better achieve germination. There are three easy methods to scarify your hard-coated seeds: the mechanical, the acidic and the boiling water methods.
Mechanical: This method involves scratching, breaking through and/or weakening the seed coat surrounding the embryo so that the embryo has a better chance during germination. Remember that you do not want to damage the embryo by crushing the seed’s coat. You just want to weaken the hard coating enough for the embryo to break through during germination. In order to do this mechanically, you want to crack the surface with a knife or nick the seed with nail clippers to cut through the coating; you can also use sand paper or a nail file, and run it over the seed, scratching at the coat to weaken it. Sand paper and nail files work best with larger seeds. Sow the seeds right after the weakening of the coating is achieved.
Boiling water: Bring water to a boil in a pot, remove it from the stove and submerge the seeds into the hot water. Allow the seeds to soak in the water as it cools down to room temperature. Once the water has reached room temperature, remove the seeds and sow them. This process helps soften the coats.
Acidic: This method can be dangerous and should be carried out with caution. Place the seeds in a glass container and cover them with sulfuric acid. Stir gently and allow the seeds to soak in the solution for around 10 minutes—this can fluctuate depending on the seed. After the appropriate amount of time, or until the coating has thinned, remove the seeds, wash them and then sow them. To be safer, you can substitute vinegar for the sulfuric acid, however it is less effective.
Which ever method you use, remember to be cautious of not crushing the embryo within the hard-coated seed. Scarification can help with germination, however it is important to sow your seeds right after you have scarified them to help improve your chances of success.
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