When to Start Cut Flower Seeds in Zone 3 (Real Dates from Our Charlie Lake Flower Field)

Quick answer

In zone 3, you start cut flower seeds by counting back from your last spring frost. Ours at Charlie Lake BC is May 15. Cool flowers like snapdragons and lisianthus start first, because they can go out before that date with frost cloth ready. Hot flowers like cosmos and zinnias start later, in April and May, because they wait until frost has passed. Below are our real seed starting dates and the dates our first stems were ready to cut.

Let's talk about seed starting for a minute.

In zone 3, the answer to "when do I start my seeds?" always starts in the same place. Your last spring frost. Every seed starting date on our farm comes from that one date, so let's start there.

What is a last frost date, and how do I find mine?

Your last spring frost date is the average date of the last 0°C night where you live. Ours at Charlie Lake is May 15. Every seed starting and planting date you'll ever need is counted forward or back from it.

It's an average, which means half the years frost comes a little later. Some years Old Man Frost shows up well after May 15, so we always keep frost cloth close by in spring.

To find yours, look up the climate records for the weather station nearest you. In Canada that's Environment and Climate Change Canada's Canadian Climate Normals. In the US it's NOAA. Write the date somewhere you'll see it all winter.

Does my growing zone tell me when to start seeds?

Not really. Your zone is about winter. It tells you how cold it gets, which decides things like whether a perennial will come back or whether you need to dig your dahlias in the fall. In zone 3 we dig ours every year.

Your frost dates are what set your seed starting calendar. Two gardens in the same zone can have different last frost dates.

Is it a cool flower or a hot flower?

This is the "but" nobody tells you.

Cool flowers handle frost. Snapdragons, larkspur, bachelor's buttons and Iceland poppies can be planted out before your last frost, with frost cloth ready. Because they go out early, they also start indoors early.

Hot flowers can't handle frost at all. Cosmos, zinnias, celosia and sunflowers wait until all risk of frost has passed. Start them too early and they sit in their trays far too long.

Some flowers sit in between. Strawflower goes out on or after our last frost, once nights stay above about 10°C.

Get this one thing right and most of your seed starting dates fall into place.

How many weeks before last frost do I start seeds indoors?

Every flower needs a set number of weeks indoors before it goes out. Count back that many weeks from the day you'll plant it out, not always from your last frost.

Here's how that works for a few of the flowers we grow:

Cosmos: start indoors 4 to 6 weeks before your last frost. For us that's early to mid April. They go out on or after May 15.

Zinnias: start 3 to 4 weeks before planting out. They go out 1 to 2 weeks after last frost, once the soil is about 16°C and nights stay above 10°C, so we start them late April to early May. Plant them out young so the roots don't get rootbound.

Strawflower: start about 6 weeks (4 to 8) before planting out. It goes out on or after last frost.

Snapdragons: start 6 to 8 weeks before planting out. As cool flowers they go out before our last frost, so they start early. Harden them off before they go out.

Lisianthus: start 12 to 16 weeks before planting out, and keep them below about 24°C. Yes, really. They're slow.

Which cut flowers can I direct sow in zone 3?

Some flowers go straight into the flower field instead of starting indoors. The trick in zone 3 is waiting until the soil can be worked, not just until the snow is gone.

At Charlie Lake our soil is usually workable in late April, about 3 weeks before our last frost. We direct sow our ammi as soon as the soil can be worked. Direct sown flowers bloom later than transplants, so plan for that.

When will my cut flowers bloom in zone 3?

Here's when some of our first stems were ready to cut, counted from our May 15 last frost:

A few things stand out. The cool flowers we planted out early gave us our first stems in June. The hot flowers came in at the end of July. Lisianthus took the longest, which is why it needs such an early start. Our first fall frost is around September 15, so in zone 3 every week of picking counts.

The honest part

Nothing really went wrong in my first seed starting season. But it took months of work before I sowed a single seed.

I had to research every variety. I built my crop plan on paper and used a free planning calculator, hoping it was right, to work out how many seeds to sow. I wrote that down, planned my next succession and did it all over again. Then I turned seeds into trays. Then I made a calendar of what to sow, how many seeds or trays, on which day, and hoped none of my numbers got lost in all the translating.

On sowing day I had sheets of paper that always ended up wet, soaked and dirty, while I tried my best to keep myself and my team organized.

It was a lot of hoping and praying!

That's exactly why I built Stemwise, a cut flower planning app that does this math for your zone, your frost dates and your beds. Stemwise is coming soon. You can start today with a free plan for your first bed at mystemwise.com.

Questions growers ask

Can I start my seeds too early?

Yes. Seedlings that sit in their trays too long get rootbound. Count back from your plant out date and start on time, not early.

What if frost comes after I plant out?

Cool flowers can handle it, so keep frost cloth ready to cover them on cold nights. Hot flowers can't, which is why they wait until all risk of frost has passed.

Can I fall plant cool flowers in zone 3?

Not here. Fall planting only works where a flower is winter hardy for your zone. In zone 3 we plant our cool flowers out in early spring instead, before our last frost.

Do I need to start everything indoors?

No. Some flowers, like our ammi, are direct sown into the flower field once the soil can be worked. Others do best started in trays.

About Cory
Cory Franklin is a retired RN who had never grown a flower before she started Franklin & Co. Flower Farm, a zone 3 u-pick flower farm in Charlie Lake, BC. She is also the founder of Stemwise, a cut flower planning app. She shares what really happens in her flower field, real dates and all, so you can grow with less guessing.

More from our flower field

• Flowers That Truly Thrive on a Zone 3 Flower Farm
• Stock Flowers (Matthiola Incana)
• What We're Doing in February on a Zone 3 Flower Farm

When do you start your first seeds of the year?

– Cory