Basil will readily pop up without any special treatment, but if you’ve had trouble germinating peas, moonflowers, sweet peas, or nasturtiums, among others, soaking or scarifying could help your success. 

Not to say that a sweet pea or morning glory seed won’t germinate if you simply plant it in the soil. Seeds want to germinate, but the conditions in our gardens often don’t mimic the environment they adapted to, which can lead to spotty germination. Soaking and scarifying seeds raises your germination percentage. Some plants need a period of cold to break dormancy, and we’ll cover that as well. 

Soaking Seeds 

Seeds have a seed coat, and depending on the plant, it can be quite hard, even stout enough to protect the seed as it passes through an animal’s digestive system. For a seed to germinate, it needs to imbibe, or take up water to rehydrate. We can get a bit of a head start on germinating some tough-coated seeds and improve our success rate by soaking them. 

Soaking seeds is merely speeding up the process by which the seeds imbibe water. What might take a couple of weeks in the soil can happen in a day or less when submerged in water. Typically, small seeds can be soaked for an hour, while large, extremely hard seeds may need overnight. Twenty-four hours is about the maximum useful soak time because seeds need oxygen to germinate. While that’s not normally a problem in soil, leaving a seed underwater for an extended period of time can suffocate it.

Soaking seeds is easy. We shake some seeds into a small glass bowl, water glass, or other container, add some water, and let them sit. After soaking, the seed coats have softened, water has begun to penetrate to the inside of the seed, and the germination process can begin. You’ll often see a change in the color of the seed, but you can also test one with your fingernail. If it is firm, but you are able to make an indention easily, it’s probably ready. As a general rule, I often simply soak any seeds that need treatment overnight and plant in the morning.

Avoid extremely hot or boiling water. Somewhere along the line, this advice got passed around, with the idea that hot water will soften the seed coats more quickly. Room temperature water is fine. Boiling water can cook the seeds, just like it would cook the beans for your dinner.

Scarifying Seeds

Scarifying means we’re going to nick, chip, cut, or otherwise penetrate the hard outer seed coating to help water get inside and get things moving. Depending on the seed size and your dexterity, there are several ways to accomplish this task.

• A utility knife (the kind with the disposable razor blade), an old dish towel you don’t care about, and a cutting board make a good seed nicking station. Fold the towel in half or into thirds, and lay it out flat on the cutting board. The towel will help keep the seeds from slipping and rolling around on you or bouncing off into the sunset if the knife slips. A utility knife is much easier to hold on to than a naked razor. The tip works well for delicate seed scoring work. Try to make small shallow cuts in one or two spots, but don’t cut deeply into the seed.

• Grab some 40- or 80-grit sandpaper, or an emery board (nail file). The abrasive particles make short work of seed coatings, but you’ll have to be careful to avoid damaging the seed embryo inside. Grasp the seed and make a couple of rubs, moving the seed on the paper, or hold the seed and use the emery board like you would when smoothing a fingernail, giving it a few strokes.

• A standard fingernail trimmer can work well for nipping off a small piece of tough seed coat. Hold the seed in one hand and use the tool to remove a small sliver of the seed coat from the end or side, wherever you can get a good purchase. Take a small piece at a time.

No matter the method, remember to go slowly until you get the hang of it. You want to weaken the seed coating, not damage the viable seed embryo inside. If you see a visible change like a thin spot or a little hole, that’s normally a good sign you’ve gone far enough. 

You may wish to make a nick or two and then soak the seeds, especially for stubborn cases like morning glories. 

Cold Stratifying Seeds

Perennial seeds often need a period of cold to break their dormancy. It’s a mechanism to ensure they don’t germinate in the fall without sufficient time to grow and establish before winter. Many of our native perennial flowers need 30 or even 60 days of chilling, depending on the species, to germinate reliably. 

To cold stratify seeds, we need a damp material, like a paper towel or moist sand, a container (plastic sandwich bags work, or a glass bowl with a lid), and some space in the refrigerator. 

For an easy way to cold stratify seeds, try this method:

• Determine how long the seeds need to be chilled. If it isn’t on the seed packet or catalog, you can look online. 

• Count back not only how early you’d like to plant the seeds, but also accounting for the chilling time. For example, if you wanted to transplant anise hyssop (Agastache foeniculum) outdoors on May 1st, you might sow the seeds indoors 6 weeks earlier, around mid-March. Since they need 30 days of cold, moist stratification, you’d begin that process in mid-February.

• Use several sheets of moistened paper towels (wring them out), place the seeds inside, and fold the paper towel over the top. Place the towel and seeds in a plastic bag, label it, and tuck it into the door or drawer of your refrigerator. 

• Set a calendar event to remind you when they are done and ready to plant.

Don’t worry about getting the number of days exactly right. Nature doesn’t use a calendar. The guidelines are more of a minimum time needed, not an exact requirement. 

Winter Sowing takes the guesswork out

If you’d like to make the cold stratification process easier and not clog your fridge with bags of seedlings, try winter sowing. It’s really just letting the normal cold outside weather do the work for you, and it can be a great way to make planting perennial seeds easy.

While winter sowing can be done straight into the garden, I prefer to use milk jugs or similar containers. I can plant, label, and set the jugs aside, and in spring, the seeds have been stratified and planted. All I have to do is provide a little care. 

Here are the basic steps for winter sowing, and you can check out our full article about it here: 

• Clean out a milk jug, juice bottle, or similar clear or clear-ish container. The slight opaqueness of a milk jug works well to shelter seedlings in spring, but nearly anything will work.

• Cut it almost in half. Leave one side to act as a hinge. A pair of scissors works well for this task, and lets you keep better control than a knife.

• Fill the bottom several inches deep with a high-quality potting mix or seed starting mix. It should be damp, but not wet.

• Sow your seeds according to their needs, at the right depth.

• Close the container and tape it shut with masking tape, then write the date and the plant variety on the tape. 

• Set the container in a sheltered spot outside and let winter take care of cold stratification for you. As the weather warms in spring, you may need to unseal the container and keep an eye on moisture, sunlight, and temperature (don’t let them bake on a warm, sunny day). 

Which seeds need what treatment?

We know how to soak, scarify, or cold stratify our seeds, but which plants need this special treatment? Start by checking the seed packet and the catalog description. Seed packets are small, and sometimes all the pertinent information doesn’t readily fit. After that, look for the gardening and horticulture section of your state’s Cooperative Extension Service websites.  

As a rule, the vegetables and most annual flowers we grow in our gardens do not need cold treatment, but those with hard seed coats will benefit from soaking or scarifying. Common seeds to soak or scarify (or both) include chickpeas, regular peas, lima beans, sunflowers (not necessary but helpful), beets, beans, large pumpkins, Swiss chard, morning glories, moon flowers, nasturtiums, sweet peas, and hyacinth beans.

Cold stratification is a common need for native perennial flowers, and it makes sense. In nature, they became mature seeds in autumn, waited for winter to pass, and then germinated in spring. Not all perennial flowers and plants need cold stratification, but to save yourself problems, check ahead of time. For those that do, remember to get started in late winter, or cold sow them in fall.