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How to Grow

Sweet Peas
This delicate flower will add height and a whimsical feel to your garden. A few key tips will help you have success with growing sweet peas in colder climates.

How To Grow Sweet Peas

by on February 15, 2024
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Sweet peas are one of those flowers that once you grow them once, you can’t help but plant them again, year after year. They are delicate, gorgeous, fragrant and can add a ton of height and dimension to your garden. In my Zone 3b garden, our sweet peas have reached over 6ft tall. They are really one of my fav flowers for their height alone. In this post, I’ll walk you through the tricks I’ve learned over the years to help our sweet peas thrive in a short growing season.

Sweet Pea Quick Growing Notes

Flower: Sweet Peas

Latin name: Lathyrus odoratus

Difficulty level: Easy to moderate

Life cycle: Annual

Sun exposure: Full-sun

Days to bloom: 60 days

Timing: Direct sow in early Spring after risk of a hard frost is gone

Planting seed depth: Sow seeds 1/2" deep

Soil needs: Well draining soil that's been amended with compost 

Where To Source Organic Sweet Pea Seeds In Canada

There’s an assortment of fantastic Canadian seed suppliers I like to shop from, all of which you’ll find listed here in my post Where To Buy The Best Organic Seeds In 2024.

The options are somewhat endless. So how do you decide who to pick?

Personally, I love Sweet Pea varieties that are offered in a blend of colours, like this Old Spice Blend, as it will give you more variety in your bouquets. I also like to pick an early-blooming variety, like this Early Multiflora Blend, so that I can enjoy my sweet peas earlier on in our short growing season.

It’s also fun to shop from smaller seed suppliers who are breeding new varieties of Sweet Peas. I love Whistling Prairie Flowers based in Saskatchewan, Canada and, of course everyone’s fav, Floret Flower.

All this to say, there’s tons of options in Canada when it comes to buying sweet pea seeds!

My Fav Sweet Pea Varieties

Mammoth Blend — huge seed pods & flowers

Painted Lady — gorgeous shades of light pink petals

Janet Scott — champagne coloured blooms

Should You Start Sweet Peas Seeds Indoors

Over the last few years I have conducted my own little “sweet pea growing trials.” I’ve tested methods of both starting seeds indoors, with the hope of getting even earlier blooms, and also direct sowing sweet pea seeds in early Spring.

After trialing both methods, I can confidently tell you that in a short season, cool climate garden sweet peas do best when direct sown’ outdoors in early Spring.

Other gardening blogs may encourage you to start your sweet peas indoors. In fact I know many do suggest this method. However, in my trials, sweet peas always do better when direct sown’ in the garden.

Here’s why starting sweet peas indoors and then transplanting them out doesn’t work in my experience.

Sweet peas have delicate roots that don’t like being disturbed, so will often die in the transplanting process.

Sweet peas germinate well in cool, cold soil and therefore don’t need to be placed under grow lights and/or on a seedling heat mat like other flowers you’d start indoors do.

Sweet peas are heavy-feeders and can produce vigorously if properly fertilized, however their growth can be stunted when started indoors as proper feeding is more difficult when in smaller containers.

Sweet peas started indoors typically need to be pruned before being transplanted out, which just adds another tedious step to growing when it doesn’t need to be that hard.

All that to say, direct sowing your sweet peas will give you big, beautiful plants with tall vines and vigorous blooms…plus with a lot less work than starting indoors!

What Is The Best Month To Plant Sweet Peas In Zone 3 & 4

In Zone 3-4, direct sow your sweet pea seeds outdoors in early Spring when the soil is workable and any chance of a hard frost has passed. This is typically early May here in my Manitoba garden.

Sweet peas are quite cold tolerant, so even if nighttime temperatures are dipping close to freezing they’ll be okay. In fact, they might even do better!

So depending on where exactly you live and your micro-climate, the best month to plant sweet peas in Zone 3-4 is likely sometime between early April to early May.

If you live in a warmer zone, such as Zone 7 or warmer, you can even try direct sowing your sweet peas in the Fall and enjoy blooms come Spring.

Should You Soak Sweet Pea Seeds Before Planting

Yes, you should soak sweet pea seeds for 12-24 hours before planting to soften the seed coat and speed up germination. Be careful not to soak them for longer than 24 hours as it could damage the seed and lead to poor germination rates.

In my trials, soaking my seeds almost always speeds up germination and has led to more vigorous plants!

Soaking your sweet pea seeds can be especially helpful if you’re working with clay-like or other heavy-soils as it gives your seed a helping hand in establishing strong roots.

How To Soak Sweet Pea Seeds

Soaking sweet pea seeds is simple.

Simply fill up a small jar or container with room temperature water and pour in your seeds.

Place the container in a safe space away from direct sunlight. I usually just tuck mine in a corner on my kitchen counter.

Let them soak for 12-24 hours before planting directly in the garden.

Do Sweet Peas Need A Trellis

Yes! Sweet peas absolutely need a trellis or support system to grow up.

Sweet peas produce heavy, vigorous vines that can easily grow over 6-8ft tall. So whatever system you choose ensure it can account for that much growth and weight.

There’s various support systems you can use, including heavy duty netting with posts on either end, chicken wire, cattle panels or other DYI solutions (Pinterest is full of them!). A garden fence would work well too.

In my garden, I’ve always grown my sweet peas up chicken wire that I secure to the ground with two lengths of lumber on either end. This approach has worked really well for us! It’s inexpensive and easy to move to a new location the following season if you like to switch up your garden annually like I do.

Planting one row of sweet peas seeds on either side of the chicken wire will result in the entire length being completely covered in vines and flowers by the end of the season. It’s really beautiful and adds great height to the garden!

5 Steps To Growing Sweet Peas In Zone 3-4

Step 1:

After soaking your sweet pea seeds for 12-24 hours in water, drain the water and bring your soaked seeds outside to the garden.

Step 2:

Select a planting area that has full sun, well draining soil and enough room for you to add in a trellis or support system.

If you’re installing a trellis (rather than planting them up a fence or existing support system), install the trellis first.

Then, dig a shallow but long trench about 2-3″ deep on either side of the trellis. The trench should be just a few inches away from the trellis.

To determine the length of your trench, count how many sweet pea seeds you have and then plan for about 4-6″ of space between each. For example 20 seeds x 6 = a trench 120″ long. Don’t get too hung up on the math though! Sweet peas are forgiving.

Step 3:

Add a generous amount of compost to the trench. Sweet peas are heavy-feeders so giving them lots of nutrient-dense soil from the get-go will set them up for success!

I like add about a trowel full of compost every 6″ or so.

You can also add a few tbsp of an all-purpose granular fertilizer to the middle of the trench. This isn’t necessary but will lead to healthier plants throughout the season.

Step 4:

Place your soaked sweet pea seeds along the trench, spacing them about 4-6″ apart. Again, the math doesn’t have to be exact but using a tool like a Hori Hori Knife could be helpful in this case.

Push each seed gently into the soil so it stays firmly in place once covered.

Step 5:

Cover the seeds with the dug up soil until they are covered by about 2-3″ of soil.

Then water heavily. Sweet peas require consistent watering for strong germination, so be sure to water daily if not twice a day if it’s a hot spring.

Seeds will germinate in 15-20 days.

How To Care For Sweet Peas Throughout The Growing Season

Once established, you’ll notice your sweet peas will put on growth really quickly and can start climbing in as little as 1-2 weeks after germination. This is why installing your trellis or climbing structure when planting is key.

As mentioned, sweet peas love water and thrive with consistent watering. From June-August we run our irrigation system along our sweet peas and run it morning and night when temperatures are high.

I will typically top-dress my sweet peas with compost once throughout the growing season (if I get around to it!). But I find it’s not completely necessary, especially if you added compost and fertilizer to your trench at the start.

Really, what will make sweet peas grow big and bold is full sun, consistent water and a vertical growing support.

If you can provide those three things, I’m confident you’ll have sweet pea growing success!

How To Grow Sweet Peas For Cut Flowers

Cutting sweet pea flowers to add to bouquets is easy! Simply use a clean, sharp pair of kitchen scissors or garden shears to snip at the stem, leaving about 3-5″ of length if possible.

While sweet peas are a gorgeous flower (and one of my personal favs to grow), they don’t necessarily make for great cut flowers.

Sweet pea blooms once harvested will only last for 4-5 days tops in a vase with water before they start to drop their petals.

I’ve found these two tricks help keep sweet pea flowers for longer as cut flowers:

1. Harvest sweet peas with pods that haven’t full opened yet. They will open inside instead and give you a few extra days as cut flowers.

2. Add a tsp or so of sugar to your bouquet water to prolong their life as a cut flower.

And there you have it!

That’s your complete guide to growing sweet peas in a short growing season like we have here in Zone 3-4.

If you have other tips for successfully growing sweet peas in a Northern climate, I’d love to hear them! Feel free to comment below. I answer all comments and love hearing from you.

All the best with your sweet peas this season.

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Latest Comments

  1. April 12, 2024

    Can I grow sweet peas and have them grow over the edge/side of a tall garden box like a trailing vine?

    Thank you

    — Wanita Fonaldson
  2. April 16, 2024

    Hey Wanita, yes you could! That’s a great idea.

    — Maggie