The seeds of some types of plants need a little help to sprout. These are seeds that have an impermeable exterior shell that keeps water out. Because of this hard coat, you can’t just toss these seeds into worked garden soil and expect a good result. Gardeners need to know how to scarify seeds to break through the coating and trigger germination.
Nature has set up this hard-coat seed system to be certain that the seeds have a hospitable environment before sprouting. But this isn’t a quick process. You won’t want to wait for this to happen naturally when learning how to germinate seeds. Before planting seeds like this, you need to practice scarification techniques that penetrate the hard coats, such as learning how to nick seeds or some other method that allows moisture to get inside the seed’s hard shell.
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What is Scarification of Seeds?
If you want to start scarifying seeds, it’s important to understand the purpose and the process. The basic concept of scarification is to create an opening in the hard shell of a seed so that water can enter. The presence of moisture triggers the seed inside to grow.
Any process that breaks or scratches the seed coat to make it permeable to water can be classified as scarification. While nicking seeds with a knife is the most common method, it is not the only way to create an opening in the seed coat. Sanding, grating, boiling, and chemical scarification using sulfuric acid are also possible.
In areas with cold winters, the dropping temperatures are sufficient to open the seed coat – a process known as seed stratification. However, it is also possible to stratify seeds at home by subjecting moistened seeds to cold temperatures in a freezer.
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Is it Necessary to Scarify All Seeds?
Anyone who has ever planted a garden knows that it is not necessary to scarify all seeds. Most seeds will grow well without scarification. The seeds that need scarification are those that have a waterproof seed coat and go dormant over winter.
Dormancy is nature’s way of preventing the seeds from starting to germinate until the conditions are favorable for the survival of seedlings. This is often the case for trees and shrubs that fruit and seed in the autumn. Since seedlings that germinate in fall are unlikely to make it through the winter, dormancy keeps the seeds “sleeping” until better conditions for plant growth arrive in spring.
Dormancy is sometimes controlled by the temperature and environment. But it can also be due to some inhibitory factor in the seed like an impermeable seed coat.
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Scarification Methods
Successful scarification can be accomplished by any method of opening the seed coat or of creating an opening in the hard seed coat through which water can pass.
For a home gardener, it is easiest to scarify seed by mechanically opening the seed coat. This means nicking seeds with a knife, grating them with a file, or hitting the seed with a hammer. Sanding can involve the use of sandpaper or can be accomplished by shaking the seeds in a bag of sand.
The key to nicking, sanding, and grating is to create an opening in the external coat without damaging the parts of the seeds inside. Likewise, if you are hammering the seeds you want to take care not to smash them, but only to crack the outer shell.
Some seed scarification methods only work for certain types of seeds, such as placing the seeds in boiling water, and then leaving them in the pot until the water cools. This is effective for lupines, sweet peas, nasturtiums, and some types of beans.
Commercial growers often use sulfuric acid to scarify seeds – placing the seeds in a glass container and covering them with concentrated sulfuric acid until the seed coat thins.
Whichever method you use, follow it up by soaking seeds before planting – a few hours or overnight in a glass of water is ideal. Then get them planted as soon as possible. Scarified seeds shouldn’t be stored because they can quickly lose the ability to germinate.
