How to Grow Zinnias in Zone 3

Zinnias are one of my favourite annual flowers. They’re easy to grow, and with so many varieties to choose from, there’s always a new favourite to discover!

A couple of years ago, I planted a forty-foot row of them, and it was pure happiness. I never imagined how much joy that one colourful stretch would bring me each day as the blooms kept coming. Even now, long after that garden has faded, those zinnias still make me smile (as you’ll see in the various photos of them in this blog post).

If you’ve struggled with growing zinnias in a short growing season or cold climate like mine in Zone 3 on the Canadian prairies, don’t worry! Here’s how you can make it work and bring those cheerful blooms to life in your garden.

Fun fact: Zinnias were my wedding flower, so they’ll always hold a special place in my heart.

A woman in a white dress and wide-brimmed hat smiles while holding a large bouquet of colorful zinnias. The bouquet features shades of pink, orange, yellow, and red. She stands outdoors with a blurred green background.

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How to Grow Zinnias in a Short Growing Season

Zinnias germinate very easily! You can direct-sow them as soon as all risk of frost has passed, or you can start them indoors. If I’m starting indoors, I do it between 4 to 6 weeks before my last frost date. You can also do a late succession planting—I like to sow another batch about 4 weeks after my last frost date. That way, if the weather stays nice, I’ll have fresh zinnias when my first batch is tired and largely unusable.

Zinnias love heat! If you have a spot in your yard that’s hotter than others, zinnias might be a good candidate for that area. They aren’t too fussy about soil, but if you have dry, sandy soil like I do, they’ll definitely benefit from extra moisture.

Three white buckets filled with vibrant zinnias in shades of orange, pink, and yellow are placed on a garden path. The background is lush with green foliage and wildflowers, creating a serene and colorful outdoor setting.

Zinnias do well in both container gardening and square foot gardening. If you’re using the square foot method, I space them 4-6 inches apart. In warmer climates, you’d probably want to space them 9 inches, but here in Zone 3, 4-6 inches works just fine. For a cutting variety in a container, you’ll want to give them more space. In a 12-14 inch diameter container, I’d only plant four zinnias.

Zinnias are cut-and-come-again, and you can even root your cuttings if you want! I did this last year because I lost quite a few plants. When I pinched them, I rooted all the cuttings. It wasn’t the best year for them, so they took a while to get outside, but the cuttings still resulted in flowers!

A field of orange and pink zinnia flowers in full bloom on the Canadian prairies, surrounded by lush green leaves. The background features a blurred view of a white tent or greenhouse and some trees, creating a serene garden scene.

When harvesting zinnias, you’ll want to do the wiggle test! When you wiggle them, make sure the stems stay straight before picking.

See the wiggle test in action in the video below:

Seed Saving Zinnias

If you really love a certain zinnia variety and want to save seeds without it cross-pollinating with other types, you’ll need to be intentional. Use a dry paintbrush to hand-pollinate the bloom: gently swirl the brush in the yellow center of the flower, then brush the pollen down between the petals and into the base of the flower head. Do this when the bloom is fully mature.

If you’re hoping to save seeds, resist the urge to cut your favourite flowers! Leave them on the plant so they have time to fully mature and set viable seed. I’ve made the mistake of cutting blooms I loved, only to miss out on seed-saving because they didn’t have enough time to finish growing.

And one more thing—zinnias are not frost-tolerant. If frost is in the forecast and you’re still waiting on blooms to finish maturing, cover them with frost fabric to protect your future seeds.

Close-up of a dry, withered zinnia flower against a blurred background. The petals are curled and brown, surrounding a dark center. The overall tone of the image is warm and muted.

My Favourite Zinnia Varieties for Cold Climates

Before we get to my favourites, a couple of notes on varieties that haven’t worked for me:

I’m not a fan of the Zinderella Series because the poof never looks quite right when I grow them.
I also am not a fan of the shorter zinnia varieties bred for pots, as most of them are single-petal varieties, which just aren’t as pretty as the doubles.

Now onto some of my favourite varieties that I grow in my Zone 3 flower farm!

Benary’s Giant Mix

A vibrant assortment of zinnia flowers displays shades of red, pink, and purple. The blossoms are densely packed, showcasing intricate petal layers and golden centers. The image highlights the flowers' vivid colors and delicate textures.

Cactus Mix

Oklahoma Series

A close-up of a cluster of orange and pink Oklahoma Salmon zinnia flowers with vibrant green leaves in the background, showcasing different stages of bloom in soft, natural light.

Queeny Lime Series

A top view of a cluster of colorful Queeny Lime zinnia flowers in pink, orange, yellow, and peach hues. The flowers are surrounded by green leaves, and they are displayed against a dark background, creating a vibrant contrast.

A Note About Zinnia Breeders

Some of the most well-known and popular zinnia breeders include Floret Flower Farm, Windfall Flowers, Blomma Flower Farm, Dawn Creek Farm, Johnny’s Selected Seeds, and Fleurelle Flower Farm. All of them have lovely new introductions each year.

I always suggest signing up for their email lists to see when their newest varieties come out. Packets are often $20 or more, but it is so worth it to support their breeding programs and for the beautiful blooms!

Two blooming zinnia flowers with light pink petals and yellow centers rise from green leafy stems in a garden bed. The plants are bordered by a strip of dark wood, with soil visible around the greenery. — Floret Originals zinnias

Have any more questions about growing zinnias in a cold climate? Let me know in the comments!

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