Which Seeds Need Scarification?
You’re ready to start your season. Your seed-starting supplies are gathered. Spring has sprung. Then, you remember the term scarification that you learned about over the winter. What seeds require that? Brush up on the basics and learn which seeds need scarification with organic farmer Jenna Rich.
Contents
Scarification is a way to break the tough surface of seeds to assist them in breaking dormancy and getting the germination process started. Gardeners use scarification to improve germination rates. Scarification increases water and oxygen absorption, made possible by opening up the seed coating.
Seeds naturally scatter when plants go to seed and are dispersed around our gardens, road banks, and forest floors. Many have a thick exterior which protects them from harsh temperatures, inclement weather, and animals.
Scarification may be done naturally, but home gardeners can complete this task at home as well to jump-start the germination process. Let’s get into the different types of seeds that need scarification.
What is Scarification?
Nature can protect seeds during their dormancy, which is several long months in harsh environments for some species. You may be familiar with “false spring” that seems to happen every year when the weather warms up, the ground softens slightly, and signs of life come back to our yards, trees, and environment. Don’t go dusting off your patio furniture and sowing tomato seeds just yet. For many of us across growing zones, there is still a lot of winter left to endure!
The worst-case scenario for a cold and frost-sensitive crop would be germinating during this period of temporary spring-like weather and then experiencing the impending cold nights as a seedling. The odds of it surviving on its own are slim to none.
The tough shells don’t allow premature germination, ensuring they won’t germinate until conditions are just right. Here are a few factors that may hurt germination rates when direct sowing, especially in the spring.
- Cold, wet soil may cause some seeds to rot.
- Pests may have overwintered in the soil or garden borders.
- Hungry voles, mice, and migratory and wild birds passing through may dig up your seeds and enjoy them as a snack.
The more efficiently seeds germinate after sowing, the better chance they have at survival. Plus, take it from someone who learned the hard way that mice and voles love spinach, peas, and bean seeds. The less time a seed takes to germinate, the more energy it can devote to growing and transitioning into its vegetative stage, and the less likely it is to rot.
Methods of Scarification
Some types greatly benefit from a combination of two different methods. Here are several different methods used to scarify to try:
Water softening
This is done by soaking seeds in lukewarm water for up to 24 hours. Depending on the seeds, those that float may be less viable.
Pro tip: Do not soak any seeds that become mucilaginous in water, like basil, chia, flax, or arugula.
Mechanical abrasion
This simple and popular method includes filing, cutting, or sanding a small area of the corner or side of a seed. A piece of 100-200 grit sandpaper or a strong nail file will work just fine. Do this just enough to nick the surface so it can penetrate water. Results are typically the best among all other methods.
Heat exposure
This method has varied results depending on temperature and seed type, so some experimentation is recommended before adding all your eggs, er, seeds to one basket. Scarify with heat by adding seeds to a warm oven or by pouring boiling water over them and leaving them to soak for up to 24 hours.
Freeze-thaw
This is a risky method that may lead to seed damage. It includes rapidly exposing seeds to alternating extreme cold and extreme heat. An easier and less risky route is to store them in a refrigerator over the winter. Allow them to come to room temperature before sowing. The freeze-thaw method is most effective and widely used with hard seed types.
Animal digestive enzymes
This is when a seed passes through an animal’s digestive tract and drops out in a different place. The act naturally softens and scuffs up the seed.
Sulfuric acid
Soaking seeds in sulfuric acid softens them and leads to a more permeable exterior, resulting in increased germination rates. This process should be monitored closely and carefully as they can easily become harmed, resulting in decreased germination rates or death.
Seeds left to their own devices in nature will eventually become nicked from being tossed around in the wind, stepped on, and from things like snow and rain hitting them.
Seeds That Need Scarification
If you’ve been gardening for some time, you may know that most seeds do not need manipulation to germinate properly. However, some species greatly benefit from a little help before being sown.
Those with a tough, thick, or waxy exterior may germinate quicker and at higher rates after this process. Most annual flowers and vegetables you may grow will likely not require scarification as they’re relatively soft.
Here are some seeds we recommend scarifying before sowing and the method best for each.
Some perennial flowers
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- Lupine seeds react well to being wrapped in a damp paper towel and chilled for up about a week. This will soften them just enough to prepare them for direct sowing. They may also respond well to mechanical scarification.
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- Milkweed seeds don’t need much scarification. Place them in a bag with coarse sand or rocks and shake it around for 30-60 seconds. Many species need cold stratification.
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- Joe Pye Weed requires a cold treatment to be scarified. Sow seeds into a damp seed-starting mix or other medium, but don’t cover seeds. Cover the tray or containers with plastic and put them in a cooler for about four weeks. After four weeks, remove the plastic and place the tray under light and they should germinate in another four weeks.
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- Columbine seeds can be chilled overnight and then added to room-temperature water for two to three days. You should see them starting to expand and grow in size. Put them back in the freezer for one night, then let them soak in boiling water for a few hours before sowing.
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- Morning glory seeds have hard, glossy exteriors. Nick them with a sanding block or clip a corner with sharp nail clippers.
Strawberries
You likely haven’t tried starting strawberries from seed at home and there’s a reason for that! While starting strawberries from seed is possible, it’s not the most common or easiest route. Plus, they can take up to six weeks to germinate. Scarifying should increase the germination time, which in turn will increase your rates.
Hard seeds
“Hard seeds” like nasturtium, lima beans, sweet peas, and chickpeas have a long dormancy, inconsistent germination, and a large, thick seed coating with an uneven surface. These might do best with a combination of soaking and nicking.
Annuals
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- Beans react best to mechanical abrasion with high-grit sandpaper or file.
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- Winter squash seeds are quite large. Using sharp nail clippers, snip off a small corner to open them up.
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- Spinach seeds are small, and since you may be sowing a lot at a time, the soaking method will work best, although nicking them with sandpaper works too.
Key Takeaways
- Do not scarify seeds until just before you plan to sow them.
- Experiment with different methods on the same type of seed until you find what works best.
- Some seeds will react best to a combination of different types of scarification.
- Be careful when using sharp tools, sulfuric acid, and boiling water, especially when kids are helping.
Final Thoughts
Scarification is a simple and beneficial process for thick, hard seeds of some of our favorite things to grow. If you’ve had issues in the past with low germination rates, critters eating your direct sown beans, or spinach seeds rotting in wet soil, I highly recommend giving this a shot. Experiment with different methods and find what works for you.
