- In nature, seeds will experience contact with sharp and rough objects that will nick or thin the outer seed coating. Even freezing temperatures assist in breaking down a tough seed coating to prepare it for germination. Seeds need water to enter the interior and nourish the embryo. Some seed coatings are too thick to allow water into the seed without harsh treatment. Any process that breaks down the outer wall of the seed enough to allow water in is scarification. Usually it involves a file or sandpaper that removes some of the seed coat.
- Boiling water seems to help some types of seeds with hard exterior seed hulls. The heat removes the cuticle and some of the lower epidermal layers to allow water to penetrate into the seed. The problem lies in recognizing which seeds respond well to this treatment. At such high heats, interior damage may occur to seeds that are not good candidate for the treatment. In these cases, a warm or even cold-water soak is recommended. Soaking the seeds in sulfuric acid also achieves the same result.
- Seed scarification with boiling water starts with immersing the seeds in four to 10 times their volume of boiling water. In some cases, the water is allowed to cool naturally for 12 to 24 hours. Many native tree seeds only need to be in the boiling water for a minute or two and then are drained and soaked in cold water. The thickness of the exterior of the seed will give a clue as to the length of time to leave in boiling water. Very thick seeds will need a longer period and seeds with thin or normal hulls just need a quick dip. Soaking too long at high temperatures can actually kill the embryo.
- Plant seeds immediately after they are scarified in the boiling water unless they still need stratification. Stratification is the means by which the seed experiences similar chilling time to what it would have experienced in the wild. This is often done in the refrigerator or the seeds are planted and the pots are placed outdoors. Chilling requirements vary by species but are usually one to three months. Direct seeding is always best if the temperatures do not forbid it. The plants can really establish a root system without getting damaged during transplanting. In cold climates, sow the seeds indoors in flats.
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