How To Scarify Seeds Before Sowing For Better Germination Rates

If your seed packet says to nick, sand, or soak seeds before sowing, that’s scarification. Scarification methods may improve germination rates in seeds with tough seed coats.

Many seeds that need scarification also need stratification (a cold chill). This explains how to stratify seeds in your fridge at home.

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Why Seeds Need Scarification

If your seed packet instructions say to pre-treat your seeds before sowing by “nicking” or “sanding” the seed coat or soaking the seeds in water—these are scarification methods.

So why do some seeds need this extra help while others do not?

It’s all about the quality of the seed coat (“testa“) and how the plant evolved.

Depending on a plant’s origins, the seed coat may be thin or thick; soft or tough.

A full-developed seed can break dormancy and germinate when conditions allow water and oxygen to reach the embryo inside.

Softer seed coats, including many vegetable seeds, take little convincing to start growing.

Others, like seeds from cold climates including hardy native plants and wildflowers, tend to have tougher coats. The tough coats, along with the need for a chilling period (stratification), are survival mechanisms which extend dormancy, but it also means germination is not as fast or easy.

In a cold climate, that tough seed coat will gradually break down from things like cold and damp conditions over the winter or animals passing the seeds through their digestive systems. By spring, when the chance of survival is much greater, the seed is ready to sprout.

When we sow these tough-coated seeds by hand, either indoors or directly in the garden, we can improve the chance of germination by using various scarification methods ahead of time. I’ve listed several suggestions below.

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Contents

• What Is Scarification?
  • Seed Examples
• How Nature Scarifies Seeds
• How To Scarify Seeds
  • Different Methods | Nicking, Sanding, Clipping, Soaking
  • After Scarification
• Resources

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What Is Scarification?

Scarification is any method that weakens or opens the seed coat or shell to encourage germination. This can involve nicking or sanding the seed coat or softening it by soaking the seed in water.

“Scarification” does not actually originate from the word “scar” but it can be helpful for remembering the term if you think of it as nicking or scarring the seed coat.

Examples of annual seeds needing scarification include sweet pea and nasturtium.

Many cold hardy perennials like delphinium and columbine also have tough coats. This group often needs both scarification, to soften the seed coat, and stratification (a chill period) over time to trigger germination. A cold, damp winter naturally provides both at once.

Some fruit and nut trees also fall into this second group. Think of apple seeds or walnuts with their very tough shells—it will take more than simple sowing to get them to grow.

Seed Examples

These are types of seeds where scarification is commonly recommended. I’ve listed the scarification instructions how they are often worded —check your seed packet in case stratification or some other prep is also recommended.

• Avocado | This shows how I sprout avocado seeds in moist paper towels.
• Angel’s Trumpet (Brugmansia spp.) | Soak seeds in warm water for 24 hours prior to sowing.
• Butterfly Weed (Asclepias tuberosa) | Start at least 3 months before outdoor night temperatures are reliably in the 50°F (10°C) range. Mix seed with a moist but not wet seed starting mix. Place mixture in a labelled sealed bad and store in fridge for 6 to 8 weeks. Some seeds may germinate in the bag if stratified too long. Outdoors: Sow directly outdoors in late fall. Seed will naturally germinate in spring.
• Canna (Canna x generalis) | File seed lightly with nail file prior to sowing.
• Citrus seeds | This shows how I pre-treat orange seeds and other citrus seeds by trimming them with nail clippers.
• Columbine (Aquilegia spp.) | Chill in moist paper towel in fridge for one week prior to sowing.
• Cypress Vine (Ipomoea quamoclit) | Nick seeds and soak for 24 hours prior to sowing.
• Delphinium (Delphinium spp.) | Use these instructions to moist-chill seeds before sowing.
• False Indigo (Baptisia spp.) | Chill in moist paper towel in fridge for 3 months prior to sowing.
• Hyacinth Bean (Lablab purpureus) | Soak in water for 8 hours prior to sowing.
• Hollyhock (Aleca rosea) | Opinions vary. If not successful with direct sowing, try 2 months of moist-chilling in fridge.
• Joe Pye Weed, Sweet (Eutrochium purpureum) | Cold-moist stratification in fridge for 2 months.
• Legumes (beans, peas, and more) | Varies – check seed packets. Soaking seeds is commonly recommended: may not be necessary.
• Lupine (Lupinus spp.) | Germination is enhanced by soaking in water overnight before planting.
• Mango | This shows how I sprout mango seeds by cutting the seed and soaking it in moist paper towels.
• Moonflower (Ipomoea alba) | Soak seeds overnight before sowing.
• Morning Glory (Ipomoea spp.) Soak seeds overnight before sowing.
• Nasturtium (Tropaeolum spp.) | To aid germination, rub seed with nail file.
• Nut and Stone Fruit Trees | Varies. Find instructions specific to species and variety.
• Poppy (Papaver somniferum) | Varies. Try cold-moist stratification x several weeks if no luck without it.
• Mallow (Abelmoschus spp.) | varies.
• Swan Gourd (Lagenaria siceraria) | For best germination, nick the seed coat.
• Sweet Pea (Lathyrus odoratus) | File or sand seed coat or clip end with nail clippers.
• Winter Squash | Soaking in warm water for a few hours is commonly recommended.

How Nature Scarifies Seeds

Nature has all sorts of ways to prepare seeds for germination. Often it’s a combination of things that, together, gradually weaken the seed coat over time and provide the conditions needed for germination—when the chance of survival is optimum.

Weather and climate play key roles. Rain and snow can both soften the coat. Freezing temperatures and freeze-thaw cycles all have effects.

Seed coats are also broken down by various microbes and fungi within the soil.

A favorite example is scarification by animals. By eating the seeds or fruit containing the seeds, their digestive acids and enzymes weaken the seed coat. If the seeds remains viable, wherever they deposit their scat (poop), is a potential new germination site.

There are countless other animal-assisted methods as well. Think of a squirrel carrying an acorn in its mouth, both scratching the surface with its teeth and fingernails (mechanical scarification) and exposing the seed to saliva (chemical scarification). All that plus burying the nut in moist soil for an extended period of time could be all that’s needed to grow a new oak tree.

Plants in some regions have also co-evolved with wildfires. For these seeds, exposure to intense heat (thermal scarification) and smoke readies them for germination. Should some much-needed rain follow, before long that field is bursting with blooming wildflowers.

How To Scarify Seeds

When we intentionally scarify seeds, we mimic various ways nature does it.

Methods used by gardeners at home generally involve sanding or nicking the seed coats or soaking the seeds in water.

No matter how you scarify a seed, there’s always a risk of ruining it. The goal is to make the seed coat penetrable to water and air without damaging the embryo and endosperm within.

When dealing with larger seeds, it’s worth looking up a diagram to learn where the embryo is located inside. On some seed coats there is a scar-like hilum which marks where the seed was once attached to the ovary wall of the mother plant. This “eye” of the seed is where the embryo forms inside and first roots and shoots emerge. Do any required nicking or sanding away from this area.

Different Methods

Which method you choose will depend on the type of seed and how easy it is to handle.

Your seed packet may suggest the best approach.

Safety first – wear safety glasses as needed.

Nicking

• Nick the seed coat with a fine-tipped knife.

Remove some of the coat without exposing the inner seed.

Sanding

• Rub seed coat with sandpaper, sanding block, or nail file.

The thicker, tougher, and larger the seed, the coarser the sandpaper can be.

I use 200 grit for most small seeds. I also have a mini garlic grater that works nicely for mid-size seeds.

Clipping

• Remove end of seed coat with nail clippers.

I do this with seeds like orange, grapefruit, and lemon.

Soaking

• Soak seed in water night (or recommended amount of time) before sowing.

Whether the water should be room temperature, warm, or hot depends on the species.

For species that can tolerate it, instructions may say to use hot (boiling) water, leaving the seed to soak until the water drops to room temperature. This is recommended for seeds like Eastern redbud tree seeds.

It is also thought that a hot water treatment could, in some instances, help remove seed-borne pathogens, although it can also reduce germination rates, particularly in seeds more than one year-old, so do your homework before trying it.

It’s interesting to take photos of seeds before and after soaking. Some swell up nicely indicating the water has indeed reached the inner seed.

After Scarification

Once you’ve pre-treated your seeds, sow them immediately. The seed will be out of dormancy and ready to grow. When growing is interrupted, seeds may lose viability or die off.

Resources

Sowing Tips

• How to Sow Native Plant Seeds Outdoors (Easy Winter Method)

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Example of a study testing different scarification methods with seeds within the same species

• Evaluation of thermal, chemical, and mechanical seed scarification methods for 4 Great Basin lupine species
  ~ Covy D Jones, Mikel R Stevens, Von D Jolley, Bryan G Hopkins, Scott L Jensen, Dave Turner, and Jason M Stettler [Source]

How to Grow An Oak Tree From An Acorn | Step-by-Step Tutorial

~Melissa the Empress of Dirt ♛