Have you ever had seeds that did not germinate for weeks or months to or never even germinated?
Do you also prefer that your seeds germinate quickly?
And that seeds that are not so fresh anymore have more chances of germinating?
Then you should definitely try scarification.
What is scarification?
Scarification is the process whereby the seed coat is damaged to break dormancy.
By damaging the seed coat, water can penetrate to the embryo and this starts the germination process.
The word scarification comes from the old Latin scarīficāre which in turn is derived from the Greek skarīphāsthai (scratches, signs). It literally means scratching the seed coat.
What is dormancy?
In nature, most seeds have a period of dormancy: a number of mechanisms prevent the seed to germinate as soon as it reaches the ground and gets some water and heat.
In temperate regions dormancy occurs in winter, when the seeds are exposed to cold for several months and start to germinate in the spring, when the temperature rises again.
In the tropics, where there are less obvious cold seasons, seeds often have a hard seed coat that takes months to be degraded by microbial activity in the soil.
In other biomes fire works as a scarification agent: there must be a fire before the seed can germinate.
Artificial scarification methods:
There are three artificial seed scarification methods:
- mechanical scarification
- thermal scarification
- chemical scarification
There are several ways to scarify seeds mechanically:
Sand or gravel:
Small seeds can be scarified in a pot containing sand or gravel, by closing the jar and shaking it vigorously until the seed coat is damaged.
For larger quantities, this is done in a drum.
Larger seeds with a very hard seed coat can be nicked with a knife or even a nail clipper.
Make sure to put the seed in a vise to minimize risk of cutting yourself.
Nail clippers for dogs are very well suited as they are sturdier than nail clippers for humans.
Larger seeds can be scarified by sanding them with a file or sandpaper.
Do this until you see the white flesh appear.
You should be careful not to file too far to avoid damaging the embryo itself.
Larger seeds with a very hard seed coat can be cracked with a miniature vise.
Such a mini vise can be found at the DIY store and is very cheap (4-5 $).
The seed can be cracked till a fissure appears in the seed coat but you can also remove the embryo (you must first sterilize the intact seed superficially).
This cracked seed or embryo should be sown in a sterile medium or sowing substrate.
The easiest way to scarify seeds thermally is by soaking them in warm water (about 80 °C) and leave them in the water until the water cools down.
In general, seeds which have sunk to the bottom can be sown immediately (there are exceptions).
If only a few seeds sank, repeat the process with slightly warmer water and then immediately sow the sunken seeds.
This may not be enough for some seeds which will need stratification.
The seed coat can also be damaged chemically.
Professional growers use sulfuric but I recommend not to try that because sulfuric acid is a dangerous product.
A safer way is soaking the seeds in vinegar for half an hour, one hour… depending on the species.
This is less effective than scarifying with sulfuric acid but it’s easy and without danger to yourself.
Rinse the seeds with clear water and sow immediately.
- Mucuna sempervirens filed seed: Own work
- Sandpaper: Own work
- File: Own work
- Mini vise: Own work
- Cracking a seed in a mini vise: Own work