Scarification is the removal or breach of the outermost seed coat to allow or improve germination.
Note: Some of the generalized statements I am about to make don’t apply to all plants, but do apply to much of what you would grow in an indoor garden. I just don’t want to bog things down talking too much about exceptions.
In the center of a seed is an embryo: this is what we want to grow into a new friend. Covering the embryo in most common garden plants is the yummy goodness of some endosperm or other stored nutrient, and the whole package is wrapped up in the seed coat.
When the seed is dry, the seed coat protects the embryo and keeps everything ready for the following season (or later). This is how seeds can be stored for long periods.
To germinate the seed: we expose the seed to water, water enters through a little hole in the seed coat called a micropyle, the water causes the interior to swell larger than can be contained within the seed coat, which breaks along stress lines, and allows sprouting to occur.
The problem is that some seed coatings can be pretty tough, especially those that in nature commonly travel through an animal’s digestive tract on the way. Some seeds must go through some form of scarification to germinate. Even seeds that can germinate without it can show an increase in germination rates.
That being said, I avoid it whenever I can, but I breed plants, and for a given variety I’ll take a seed that sprouts on its own over one that has to be treated every time. Alas, sometimes you have no choice, as some plants must be treated to germinate.
Basically, all you are trying to do with scarification is weaken or pierce the seed coat without damaging the interior.
The two main forms of scarification are mechanical and chemical.
Mechanical scarification just means that you physically abrade the seed coat with a tool: drill a hole, nick the edge, use a file and so on. My current favorite method uses an emery board. Take a very small box or bottle, cut the emery board into small enough pieces to fit, add the seeds, close the container, and shake. By and large you don’t want to try to remove the entire seed coat, just weaken it.
Chemical scarification is taking the seed and exposing it to a chemical to weaken the seed coat. Acids replicate the process of going through a digestive system. While sulfuric acid is commonly used professionally, I have read that both vinegar and hydrogen peroxide are safer alternatives. I haven’t tried them before, so let’s try it.
Here we go.
I have four groups of twenty catnip seeds.
- Group one will not receive any scarification treatment.
- Group two will be exposed to light emery board sanding (shaking).
- Group three will be exposed to a 3% solution of hydrogen peroxide for 5 minutes, then rinsed.
- Group four will be exposed to 5% acidic vinegar for 5 minutes, then rinsed.
If you look closely, you can see at a slight cosmetic difference between the untreated (far left), and the treated seeds. I suspect the floating seeds are dead, but did not remove them in case they are not.
After five minutes had expired, I used a garden hose screen as a filter, and rinsed the seeds. The seeds are now ready to attempt germination.
Once seeds are treated, they should be started without delay, as the protective seed coat has been damaged.
Peace, love, and puka shells,
Grubbycup
Read on to see what happens next!
I can’t wait to see the results of your experiment! Very interesting.
glad to see someone with an interest in increasing germination rates. 5 years ago i began experimenting with H2O2 during the germination phase. now i wouldn’t even attempt to sprout a seed without it. I’ll share my results, tips, and techniques…
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you’ll need:
H2O2 (3% solution for the measurements listed)
DISTILLED/R.O. H2O (tap = no bueno)
Superthrive (optional)
Glass or other non-reactive container (no metal, wood, or paper) like a mason jar or a 20oz soda bottle.
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a few notes… don’t prepare this solution in advance. make it when you need it and use it immediately. H2O2 breaks down quickly (more so in the presence of light) and will yield the solution impotent for germination purposes.
begin by adding 0.5mL of Superthrive to a gallon of water. I’ve found Superthrive to promote vigorous root growth in the first week out of the shell. if you don’t have any Superthrive that’s OK, but its a staple in my garden and a great product. the remainder of this gallon can be dumped in the reservoir after the next step… i prepare a gallon because Superthrive is so concentrated and working with smaller amounts allows less room for error.
now the container… i use a mason jar. pour 200mL from the gallon of solution in the jar. that should be enough to cover your seeds depending on their size. it should also leave you with some room to add the H2O2 and for seed displacement. add 10mL of H2O2 per 100mL of solution… so in my 200mL i will add 20mL of H2O2.
finally, place the seeds in the jar and leave them for 24 to 36 hours for hard seeds, 8 to 12 for small or thin shelled seeds. that’s it! one thing to keep an eye on is the temperature… not too hot or too cold. also, keep them out of sunlight so the H2O2 doesn’t break down before getting a chance to soften the shells.
using the above method, you will see quicker germination with a higher success rate and faster root development… i’m proud to say i have a 99% success rate and can’t remember the last time a healthy seed ‘didn’t work.’ I’ve even had luck getting physically damaged seeds to germinate using the soak method.
and lastly… i read that you planned to wash the H2O2 off the seed. no need to do so when using a 3% solution as it will break down very quickly in contact with air. also on the bag/paper towel method of germination: in my years i have found that when a seed begins putting out its taproot it wants to latch onto something, namely the paper towel. when you remove the seedling from the towel, the tough paper will actually rip off the tiny hairs coming from the taproot. this will stunt the seedling best case… worse, it could kill it. i suggest placing the treated seed directly in your medium (i prefer the Grodan A-ok 1×1’s) to minimize root damage.
thanks for bringing up a generally overlooked and unexplored topic! i look forward to your results from the other methods you are experimenting with.
Jim
Wow, thanks for the information Jim.
It sounds plausable to me, enough to pique my curiousity…
Stay tuned.
No matter what I do I cannot get catnip seeds to germinate. Is there anywhere in the world that sells catnip plugs?