Should You Soak Sweet Pea Seeds Before Planting?

Should You Soak Sweet Pea Seeds Before Planting?

Should You Soak Sweet Pea Seeds Before Planting?

If you've grown sweet pea seeds before you will probably have heard that you should soak your seeds. And... you've probably also heard that you should not soak your seeds. Soaking sweet pea seeds is supposed to soften the tough outer skin so that the seed can germinate more easily. BUT, some experts will say that soaking will reduce the germination.

It's conflicting advice and confusing too because I have soaked sweet pea seeds and they have grown. And... I have sown seeds just as they are and they have grown. I find that sweet pea seeds usually have a very high germination rate (if using fresh, good quality seed), but I have never kept a tally of how many seeds have germinated using the soak or no soak methods and I never expected it to be 100% either way.

Finding I had a little extra time this autumn, I thought that I would do a small trial to find out what germination rates I got with soaked and unsoaked seeds. I tried to set this experiment up in as scientifically as possible (yes, I thought back to high school days of sciences class reports comprised of 'Aim', 'Method' and 'Conclusion'), but it was just a test carried out in my boot room, so take from it what you will!

I started with a few hundred sweet pea seeds - all freshly harvested this year and of the same cultivar. I then selected 100 seeds that were uniform in shape, size and color and divided them into 2 groups of 50 and placed them in jam jars.

50 seeds were then soaked for 12 hours and 50 seeds were left dry.

Meanwhile I prepared two identical 50 cell seed trays with moistened potting soil.


Planting Depth

Over the many years I have grown sweet peas, I have always thought that one major factor that influences how many baby plants I get is the depth at which the seed I placed in the soil. The general rule of thumb is that a seed should be planted 2 or 3 times as deep as it is wide. However, I have found that sweet peas germinate better for me if planted a little more shallow than that - about a ¼ inch deep seems to work well.

I use a Ticonderoga pencil to make the holes for my sweet pea seed because the rings on the end are conveniently spaced at ¼ inch (remove the eraser to make this work!). Take a ruler and pencil and you will see what I mean.

I followed this rule for this 'experiment' and made sure that each seed was covered by no more than ¼ inch of potting soil.


The seeds were kept at around 63F simply because that was the ambient temperature of the room they were in. Sweet pea seeds can germinate at lower temperatures, but this was the temperature I had.


Once I planted the seeds, I did not water them again until I saw germination occur i.e. seedlings start to emerge (always exciting, no matter how many times you see it!).


I excluded light until germination occurred using a seed tray turned upside down over the plants cells.


I observed first signs of germination after 3 days, but I waited a full 14 days before counting how many seedlings I had in each of the groups. Once I saw babies emerging (day 3), I placed the trays in full light.


Thank you for reading this far, or did you just skip down the page to the 'results' section? Either way, thanks for checking out my post! The unsoaked, fresh, good quality seed won! I got 100% germination rate on the unsoaked seeds! I was surprised at that because (as I mentioned above) I don't usually expect 100% germination rate in ANY seed I plant.

The soaked seed didn't do too badly either. Only 3 of the seeds failed to germinate. That means that the soaked seeds had a 94% germination rate. Doesn't sound too bad hey? And really, for most of us, a 94% germination rate is going to be just fine. If you soak 10 sweet pea seeds to grow in your garden, then you probably won't notice the one that doesn't make it.

Worth noting: I only tested one sweet pea cultivar.  Sweet pea cultivars will all likely have different rates of germination - the cultivar I tested just happened to have a great germination rate whether or not I soaked the seeds, plus the seeds were fresh and of good quality.  You may see different results on different sweet pea cultivars and with seeds that are older etc.

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Judy beck(not verified)
May 24, 2020 at 12:03 am

My first year to plant your seeds and had about 97% germination rate! Plants are now about 5" tall, side shoots starting and getting planted out tomorrow on willow teepees. So excited to see these plants thru to flower stage. Concentration this year is all on sweet peas. Thanks so much for all your helpful information. These are my absolute favorite flower.

Diane Janisko(not verified)
January 9, 2020 at 7:16 pm

What type of potting soil do you recommend?i have used miracle grow with fertilizer in it but wondered if you had a preference.
Also, do you recommend planting in big garden pots or directly in the ground?
How tall do these plants grow?
Thank you so much.

January 10, 2020 at 6:03 pm

I use a local potting soil called Happy Frog. While you may not be able to buy that in your area, I'm sure that you can buy something similar. 

I don't recommend direct sowing.  Start your seeds in smaller pots - 4" pots work well, although you can use Rootrainers which are great for sweet peas.  Plant your sweet peas out when they are about 5 inches tall.  Sweet peas grow about 6-8ft tall.

Scott-Yellowstone Arboretum(not verified)
November 23, 2019 at 8:53 am

We were donated seeds from a woman who said they come from a perennial bush that looks like a sweet pea when flowers emerge. The seeds strongly resemble Sweet Peas. We will try your soaking and non-soaking methods. I don't know what this "bush" could be. We are located in Zone 4.

Kozmoz(not verified)
June 11, 2019 at 9:39 am

That's great! I watched a man from the UK on u-tube. He said just lay seeds on top of a damp paper towel over night.
I tried that. Only I was busy. So I left them for 4 days on top of a paper towel and just barely added water. Day 3 half the seeds already started to germinate.
On day 5 a cloudy day I planted in shallow groove in my raised bed. Covered with soiled mix. Now waiting to see what happens.

Georgina(not verified)
June 11, 2019 at 1:18 pm

I use the 'paper towel method' to germinate sweet peas, but seal them in a plastic bag so that I don't have to think about keeping it moist.  I get really good germination that way and it's good for germinating large amounts of seeds.  I always start my plants in pots rather than directly in the ground because too many creatures (snails, mice etc.) love germinating sweet pea seeds and will eat them up.  Thanks for your comment :)

Jennifer (not verified)
November 4, 2018 at 12:50 pm

Great job on the sweet pea trial! Thank you for this information! I wondered why my germination for the Elegance series was so bad...I soaked them, and I planted them too deep in my soil blocks. I will plant your seeds dry. Thanks for this!

Georgina(not verified)
November 4, 2018 at 2:30 pm

Thanks Jennifer!  You may still be able to take cuttings from your Elegance seedlings to increase the number of plants you have.  I'll be putting up a post about how to do that soon, but you should be able to find some information about it if you are interested in doing that.

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