by Erin Marissa Russell
Have you run across instructions to use hot or cold stratification or scarification but aren’t sure how and when to use these pre-planting treatments? Taking the time to learn these simple tricks and stratify seeds when directed can literally save a gardener years, as that’s how long it can take for unstratified seeds to start the growing process.
Seed treatments speed up and improve germination, and some plants need this extra push more than others to sprout successfully. Simply put, stratification (warm or cold) and scarification are techniques gardeners use to artificially replicate natural germination conditions. Scarification puts cracks in the tough exterior of a seed, while stratification mimics winter conditions so plants anticipate the growth of spring.
Each plant is truly a product of its environment, whether seeds have evolved to be scattered by gulls across sand dunes or take root in the forest thick with trees, snug under a sea of skeleton leaves. During the winter season, exposure to animals and the elements are natural sources of stratification and scarification.
Gardeners can play on the fact that each flower, herb, vegetable, and succulent species is sensitive to its habitat by faking that habitat’s wintertime conditions to kickstart germination. The rhythms of the seasons and the climate of a plant’s territory determine which of the various pre-planting treatments will signal that it’s time to start duplicating some cells and putting out roots.
There’s nothing worse than ordering a plant on your wish list, carefully sowing and babying the seeds, then having none sprout (or waiting years) just because conditions aren’t ideal. Keep reading for a breakdown of the different seed treatment techniques and exactly how to put them into action for more successful germination with those fussy plant varieties that need a little extra help from you. At the end, you’ll find a list of seeds that require pre-planting treatment.
How to Use Cold Stratification
If instructions just say to stratify seeds and don’t specify cold or warm stratification, cold stratification is what you should use.
FRIDGE OR FREEZER METHOD
Moisten two paper towels, and sandwich the seeds you’re stratifying in between them. Slip this into a Ziploc bag. Alternatively, you can use any container with an airtight lid and moistened peat, sand, or the aforementioned wet paper towels. Store your Ziploc or container of seeds in the fridge or freezer, checking every so often to make sure water is available, and add it if needed. Remove the seeds and plant them in a couple of days unless your plant’s instructions indicate a different stratification period.
OUTDOOR METHOD: COLD WEATHER ONLY
Sow the seeds you wish to stratify in peat pellets or your preferred seed-starting medium. Store these outdoors (optionally in a cold frame) for seven to 10 days. After this period, bring the plants indoors to spur germination. (Remember, this particular strategy only works in recommended growing zones when you’re planting according to schedule.)
How to Use Warm Stratification
For warm stratification, follow the instructions above for the cold stratification fridge or freezer method, but instead store your seeds in a spot that’s between 68 and 85 degrees Fahrenheit. Take a look every few days to make sure there’s still water for the seeds, adding more if needed. Follow the specifics in your plant’s instructions regarding how long seeds should be stratified.
COLD WATER STRATIFICATION
Soak seeds in cold water, changing the water daily. Leave seeds in the water for two weeks before sowing them,
Wet a paper towel, and place seeds on it inside a plastic Ziploc bag. Keep in the freezer for up to two or three months, watching for signs of germination or rotting (such as brown spots). Plant seeds when they begin to germinate, or after three months regardless of germination,
How to Scarify Seeds
Scarification is needed for some species because they need the watertightness of a solid hull to make it through their dormant period in winter. However, water has to reach the seed before it can begin sprouting. Without human intervention, this happens as the That’s why when you’re instructed to use scarification, you’ll just need to nick a seed’s outer shell to give it access to moisture.
BOILING WATER SCARIFICATION
Bring a pot of water up just to boiling (180 degrees Fahrenheit or 82 degrees Celsius). Add seeds and soak them until the water cools. Most seeds will sink to the bottom of the pot. Sometimes, seeds that don’t sink to the bottom will not sprout. When you use boiling water scarification, plant seeds on the same day as the treatment. You have the option of storing seeds in the freezer the day before boiling water scarification.
You can scarify seeds yourself by rubbing them gently with sandpaper or using a microplane grater, file, knife, or nail clippers to nick the hull. Be careful not to damage the seed inside the hull (or your hands) as you work. Some seeds are more difficult to scarify than others, so if you’re having particular trouble with one, consider using the cold weather method described below. You can also scarify seeds by shaking them in a jar that also contains sandpaper. When the seeds have changed color, they’re scarified.
OUTDOOR METHOD: COLD WEATHER ONLY
Simply leaving seeds outdoors during the chilly winter will result in scarification. After all, this is how the process works in nature.
Be Sure to Pretreat Seeds of These Plants
It’s usually perennials that need to be stratified. Because annuals wouldn’t need to overwinter, they shouldn’t require a simulation of winter conditions. If you aren’t sure of the difference, we’ve broken down the difference between perennials and annuals for you. Tree seeds, native wildflowers, and plants from the pea family often need stratification or scarification. The list below is not all-inclusive, so cross-reference it with the instructions on the seeds you would like to plant.
Green wizard coneflower
Penny black nemophilia
Red pasque flower
Sloes (also called blackthorn or Prunus spinosa)
St. John’s wort
Purple hyacinth bean
As mentioned above, this list of plants that require seed treatments is not comprehensive. Additionally, if the instructions for treating your seeds differ from what’s outlined here, always follow the specifics for the seeds you have in hand. You can use these instructions and guidelines to help you in case your seeds are missing their instructions—or just to learn about the different pretreatment methods and the steps to take to carry them out.