Seed Scarification is the process of opening up, or penetrating the hard outer shell of a seed. There are several methods to scarify a seed. I will explain all methods with examples, pros and cons below. I’ve used these methods to germinate hundreds of various flowers and legumes over the years, and they are simple and work well.
The most common ways to scarify seeds use one of the following methods, in no particular order:
- Rubbing the seed on sand paper
- Using a knife to scarify seeds
- Rubbing the seed on a metal file
- Soak the seed in hot water
- Nick the edge with nail clippers
- Chemical scarification with sulfuric acid
Note that Scarification, the act of penetrating the hard, outer shell of a seed is completely different from stratification. To read about the cold moist stratification, or cold treatment of seeds – read this article.
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1 – Sandpaper to scarify seeds
Using sandpaper to scarify the seeds is simple, cheap, and effective. It particularly works on legumes such as Lupine, Baptisia, or Partridge Pea. Perform the following steps to scarify seeds using sandpaper
- Obtain a small sheet of sandpaper. 150 grit seems to work great for me. But I wouldn’t go any coarser than 100.
- Place the seed on the far side of the sand paper. Press your finger firmly on the seed. But take care not to crush the seed.
- While applying pressure, drag the seed across the sand paper towards you.
- You can pinch the seed too – if it is large enough. But dragging it across the sandpaper works just fine.
- Repeat this process several times
- Examine the seed. Look for any discoloration (usually white) where you have penetrated the outer shell.
- Once you have penetrated the outer shell, you are done. The seed is now scarified.
Alternatively, you can actually place the seed between two sheets of sandpaper. And just rub the sheets together. However, I find that sometimes the seed just rolls using this method.
This is probably my most preferred method to scarify seeds. It is quick, easy, and isn’t messy. It is also about the least complicated, and safe.
2 – Using a knife
Another method that can work, particularly for larger seeds is a knife or file to nick the outer wall. The key thing is you need to be able to firmly hold the seed in place to do this.
- Place your seed on a cutting board.
- Hold your finger and gently apply pressure to seed. Just make sure it doesn’t move when nicked with a knife
- Carefully use the knife to cut the outer edge seed. Just cut the edge. Remember, there is a hard, thin shell. So, you should barely be cutting the seed.
- If you can see ‘white’, then you are done
3 – Using a metal file
This method is similar to sand paper. But instead of sandpaper you can use a flat file. Just lay the file flat on table or work bench with the handle pointing away from you.
- Lay the file on a workbench or table with the handle pointing away from you
- Place your seed on the file, closest to the handle
- Use your finger to apply gentle, but firm pressure to the seed
- Drag the seed along the file towards you
- Repeat until you have penetrated the outer shell
4 – Using hot water
Using near-boiling water is an excellent way to scarify seeds. And, I’ve found it to be the most effective method for scarification on the Eastern Redbud Tree. Here is the process:
- Place your seeds in an empty coffee cup
- Boil a small amount of water on the stove.
- Remove the pot from the stove, and wait 10-30 seconds for the water to stop boiling.
- Pour some of the water into the coffee cup with seeds.
- Let the seeds sit overnight. Then plant the next day.
To see the effect of this method, look at the image below. This shows two seeds from an Eastern Redbud Tree. One in which the seed was scarified and has imbibed water. While the other dry seed is so much smaller.
I should also note that the hot water method produced a higher germination rate for my Eastern Red Bud tree seeds……
5 – Using finger nail clippers to scarify seeds
You can actually use finger nail clippers to scarify large seeds. Just use tweezers or pliers to have a firm grip on the seed (without crushing it), and use the clippers to nick the seed coating.
6 – Using Acid to Scarify seeds
Some greenhouses and universities have shown that soaking seeds in a solution of sulfuric acid can sufficiently weaken the seed coat to achieve scarification.
I must be up front – I’ve never attempted this method. I don’t have sulfuric acid laying around for me to even try it. And, sulfuric acid can cause significant burns and other hazards.
But, as stated in the reference, you can soak seeds in sulfuric acid for a few minutes to a few hours to soften/remove the seed coating using a glass jar. Then, wash the seed with water to remove the acid, and plant.
Complete Video Guide, Step By Step on how to scarify seeds
What is the best method of Scarification?
The truth is there is no single method that is ‘best’. But certain seeds respond well to certain methods of scarification. Nature loves variety.
For instance, most legumes like Blue False Indigo, Partridge Pea, and Showy Tick Trefoil respond well to the sand paper, knife, or file method. While other species such as Eastern Redbud Tree and Winecup Flower (Callirhoe Involucrata) do best using the hot water method.
Scarifying seeds with rough surfaces
In fact I should expand on the Winecup Flower as it has a unique seed with a rough, or honeycombed surface. See image below:
This rough surface would be difficult to scarify with sandpaper or a knife, as the shell is quite hard, uneven, and brittle. On top of this, the seed is only 2-3 mm wide, and about half as thick.
So, like most seeds they are a bit tiny to grip/pinch. But, the rough surface of this seed would make it difficult to know when it is scarified. Plus, it is light in color.
So, determining if we have successfully penetrated the outer hull would be difficult. Thus, hot water soaking is the best method of scarification for Winecup flower.
The above methods work well for scarifying seeds. I’ve germinated hundreds of seeds using these methods. You should research your species/seed to see if anyone has already determined the best scarification method. Although, if I’m unsure, I generally opt for the sandpaper method.
Most seeds that need scarification though also need stratification. So, make sure you head over to our guides on winter-sowing and cold moist stratification. In those guides, I show you my exact process I use step by step to cold moist stratify and wintersow native perennial seeds.
PIN IT FOR LATER:
 – Effect of Acid Scarification on Lupine Seed Impermeability. Robert E. Burns. Plant Physiol. 1959 Mar; 34(2): 107–108. doi: 10.1104/pp.34.2.107
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