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The Great Sweet Pea Sowing Experiment

Sweet peas are one of those seeds that everyone has their own trick for when it comes to sowing. Some say to soak them for a day in water, some say to germinate them on a damp tissue, others say just plant them as regular.

Well, I have decided to run a big experiment this spring in order to test lots of different methods. The main results I’m looking for are germinating time and germination rate. I will be sowing two different varieties of sweet pea. I will be using spencer mix and Wiltshire ripple for the test.

The different sowing methods I will be using are as follows, soak for 24 hours, soak for 48 hours, damp tissue, straight into compost, and stratifying (freezing) soak for 24 hours (heated seed mat), soak for 48 hours (heated seed mat), damp tissue (heated seed mat), straight into compost (heated seed mat), and stratifying (freezing then heated seed mat).

The Seeds For Soaking
The Seeds For Soaking

All seeds are in the same compost and will be on the same windowsill so soil quality and the light amount should not play a factor in this test.

I am trying to be as scientific as possible but at the end of the day, I am just a man trying to grow some sweet peas in his kitchen so there are limits!

Heated Seed Mat
Heated Seed Mat

The Results

These sweet peas have been going for a few weeks now so it is time to bring you some results from my experiment and find out what the best method, for me at least, for sowing sweet peas was.

Germination Rate

So let’s start with the germination rate, this will be calculated using the number of seeds that successfully germinated within 2 weeks of the experiment start date.

First up we have the results from the heated seed tray. This seed tray was placed on a heated seed mat throughout the experiment.

Heated Seed Tray Germination Results
Heated Seed Tray Germination Results

With the heated seed tray, it is a very clear win for just regular old planting in terms of germination rate. All 8 of the regular seeds planted in the heated seed tray germinated.

Now let’s have a look at the results from the other seed tray which wasn’t heated at all. The seeds trays were side by side and used the same compost. The only difference was one was on a heated mat and the other not.

Normal Seed Tray Germination Results
Normal Seed Tray Germination Results

And surprisingly there is actually a lot of difference here in the performance of the different levels with soaking the seeds for 48hr in water before planting actually providing the best germination rate.

Now I will combine the results of the two seeds trays to give an overall result for each different method of sowing sweet peas.

Overall Results Germination Rate
Overall Results Germination Rate

So the overall winner when the trays were combined is sowing the seeds straight into the soil without any soaking beforehand.

Germination Time

So now we have looked at the germination rate it is time to look at the germination time, the amount of time from sowing until the seed has germinated and is poking above the soil.

Heated Seed Tray Days to Germination
Heated Seed Tray Days to Germination

In the heated seed tray, the soaked seeds germinated the quickest with the 48 hour soaked ones germinating fastest of all but remember only 50% of them did germinate at all!

Regular Seed Tray Days to Germination
Regular Seed Tray Days to Germination

Onto the regular non-heated seed tray and the regular straight into the soil seeds germinated the quickest here.

One thing that does really stand out though is that the seeds in the heated tray did germinate a lot faster than the non-heated ones. In the heated tray, they averaged 7.2 days while in the non-heated they averaged 8.2.

while that doesn’t sound like much it is skewed a little by the stratified (frozen) seeds which took forever to germinate. If we take those out of the results then it is 6.3 vs 7.9 days.

So what’s the winner?

I think what this shows more than anything is that the method for starting your sweet pea seeds doesn’t make too much of a difference in the end. You can soak them, plant them straight away or even freeze them and the difference will still be fairly negligible in the long run.

One takeaway though for me is that the heated seed tray does make a difference and that soaking doesn’t make much of a difference. So for ease of use, I would say planting the seeds straight away into a heated seed tray makes the most sense.

For more information on growing sweet peas from seed make sure to check out my comprehensive guide.

Paper towel

this method really didn’t work for me as the seeds didn’t do anything. If I planted them then I am sure they would germinate and grow but it’s a pain to keep wetting the towel and you don’t seem to gain anything. Definitely the most labour intensive of the methods and with no gain.

Seeds on tissue after 2 weeks
Seeds on tissue after 2 weeks