Soaking seeds to speed germination
Garden of Eatin', Seeds & Seedlings

Soaking Seeds to Speed Germination

I’m often the first to admit that there’s not much you need if you want to start from seed — just a good growing medium, sunshine, and water.

But sometimes there are forces working against us, and if there’s a way to boost our chances of seed starting success, I’m all for it.

Take, for instance, tomato seeds. Those hardy specimens have germinated on their own for generations without any interference from us well-meaning gardeners, but fermenting them before drying and storing them gives the seeds a great start come springtime.

Pea seeds are another example. They’re among the easiest of seeds to sprout, but because they grow in cooler weather, the timing can be a little tricky. Sow them too soon, and they could rot in the ground from a cold and rainy spring. Sow them too late, and they could struggle to flower once the heat sets in. The same goes for sowing them too late in fall as well; a sudden frost might hit before they have a chance to germinate.

Pea and squash seeds

Despite being cold-tolerant, pea seeds prefer to sprout in daytime soil temperatures of 60°F to 80°F. Temperatures below or above have a significant impact on germination, either by delaying the process or causing the seeds to decay altogether. While peas will still germinate when the ground is 40°F, it could take a month or more before you see the first sprout! So for maximum production in the shortest amount of time, plan for putting your peas out when the soil is still fairly warm.

To ensure the seeds will germinate the same week (and take away any uncertainty as to weather), I like to soak them before sowing the seeds outside. This method is sometimes referred to as presoaking.

Presoaking pea seeds

All seeds need moisture. As you may have learned in my seed anatomy post, the seed itself is actually a seed coat (like a coat of arms) that protects the embryo (future plant) inside. The seed coat stays intact until the proper conditions (temperature, moisture, lightness or darkness) present themselves for the plant to emerge.

Once the temperature feels just right, and there’s enough moisture to cause the seed coat to swell and rupture (thereby releasing its food stores and coaxing the embryo to develop), you have germination.

If it is too cold or too wet, too warm or too dry for that particular seed, it will fail to germinate at all. By soaking seeds ahead of time, you remove some of those barriers so that the seeds are ready to sprout by the time you stick them in the soil.

Soaking is particularly useful for gardeners with heavy clay or super sandy soil. Clay is difficult to moisten evenly if it’s allowed to dry out; and once it does stay wet, it can hold moisture for too long, causing seeds to rot. On the flip side, sand drains very quickly, making it a challenge to keep seeds (especially those near the surface) moist enough for germination to occur.

If the seeds are already wet, and the seed coats have absorbed enough water for the first root to emerge, that could mean a much earlier harvest than sowing seeds that were dry. It also relieves some of the stress of ensuring your soil is adequately damp after you’ve sowed a row of seeds — a task that’s a little trickier when starting seeds outside versus inside.

What to Soak

Soaking is beneficial for pea seeds as well as other seeds with thick, hard coats, such as fava beans (Vicia faba), beets, cucumbers, corn, and squash. Big seeds. Wrinkled seeds. In general, the tougher the seed, the better it will fare with soaking.

Fava bean seeds

Beet seeds

You can actually do this with any seed, including flowers and herbs, though I feel the smaller ones (like carrots, which are among the slowest to germinate, ironically) are too troublesome to work with when they’re wet. If you don’t mind pouring all the seeds on the soil and thinning them out later, go for it!

Common bean seeds (Phaseolus vulgaris) are actually quite thin, despite the shiny, hard appearance of their seed coats. They don’t benefit all that much from soaking, but should you insist, that brings us to…

How Long to Soak

Throw your seeds into a small bowl or glass filled with warm water (just enough to cover the seeds). For thick-skinned seeds like peas, aim for 8 to 10 hours (or overnight, assuming you soak them before bed and sow them in the morning). For thin-skinned seeds like snap beans, soak for 2 to 4 hours.

Soaking pea seeds to speed germination

Presoaking legume seeds

For all other seeds in between, the appropriate length of time to soak is more an art than a science. You want to soak them long enough so that the coats begin to swell, but not so long that they just split or rot. A safe place to start is a couple of hours; after that, check your seeds every hour until they plump up. Anecdotal evidence abounds for people who have soaked seeds for up to 24 hours without issue (such as the case with okra), but this is really a matter of try-and-see.

There might be a few floaters, but contrary to popular belief, this does not necessarily mean the floating seeds are “bad.” They’re soaked for such a short period of time that it isn’t possible to tell whether or not they’ll germinate — sometimes they will.

Floating fava bean seed

Seeds may float because they lack viable embryos or nutrient stores, making them less dense than “good” seeds that sink. Or, they may float because they have air pockets inside, which don’t always affect seed vigor or viability. The only sure way to test germination is to use the coffee filter method.

When to Sow the Seeds

Once the seeds soften a bit and start to swell (an appearance you’ll become familiar with the more often you soak your seeds), sow them in the ground immediately. You’ll often find that by soaking your seeds ahead of time, you’ve shaved a few days to even a week or more off the germination time.

Swollen pea seeds ready to be sowed

Presoaked seeds

Keep the soil uniformly moist and you should see the first sprouts within a couple of days. Congratulations, you’ve just given your crop a head start on life!

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  • Rosie

    What a fascinating post. I love your posts that get down into the science of plants and gardening – always so well-researched and well-written. Just something that jumped out at me though – a coat of arms is not the same thing as a suit of armor! 😛

    • I’m so happy you found this and my other posts useful! (And good catch, by the way — I’ll change it!)

  • FARMER LIZ

    Great info! I knew to soak beets and chard, so last time I planted them at the same time as beans, I soaked the beans too. I think I got better germination (even though you said its not necessary for beans) because I often find the the beans rot. I have problems with knowing exactly how much to water. This time I just planted them and left them alone until I saw sprouts, much more effective 🙂 Thanks for the explanation though, its good to know why it works!

    • Keeping newly planted seeds adequately moist can be tricky! I’m so glad soaking works well for you!

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