Our favourite hardy annuals for spring transplanting.
I honestly can't get enough of cool flowers. These hardy annuals thrive in the cooler temps of early spring and bring some color to the garden much earlier than their more tender friends!
The stunning peach Icelandic Poppies at the top of this bucket of blooms are one reason everyone loves cool flowers!
In Part I, I shared some of our favourite hardy annuals for direct seeding. In this post, I’m covering the flowers we prefer to start indoors before transplanting them into the garden.
Starting seeds indoors requires the right setup — a greenhouse or indoor growing area with lights and heat mats. Without enough light or warmth, seedlings tend to become leggy and weak as they stretch in search of better conditions. If you’re not set up for indoor seed starting, you may want to head back to part I and focus on the varieties we direct seed instead.
I'll assume you have some experience starting seeds indoors for this post. If not, I’ll be sharing a beginner-friendly post on that soon.
Why I start seeds indoors
- Get a jump on the season
- Some flowers require a long time to get established
- Some seeds are expensive, and I don't want to waste them
- I want full beds without empty spots.
- Larger transplants help me stay ahead of weeds.
Ok, and maybe I'm also a bit of a control freak 😉
Look at this beautiful bed of 'Chantilly Light Salmon' snapdragons!
When to Start Your Plants
To figure out your seeding and transplanting dates, start with your average last spring frost date.
As a general rule, hardy transplants can usually be planted out about 4–6 weeks before your last usual spring frost date. So, for example, if May 21 is your average last frost, counting back four weeks would put you at April 23.
Once you’ve calculated your transplanting date, you can work backward again to determine when to start your seeds indoors. Depending on the flower, most should be started about 4–8 weeks before planting out (see chart below).
If you’re unsure of your average last spring frost date, check out these average dates from Vesey's seeds.
Keep in mind that this is just a rule of thumb, and you may need to adjust based on your location. For example, if you still regularly experience hard freezes in late April, you’ll likely want to push your planting date back a week or two.
I’d also caution you not to push these dates too far in the name of getting ahead. Plants can get set back if they outgrow their plugs or pots, and you may not end up any further ahead than if you had simply waited another couple of weeks to start. Trust me — I’m speaking from experience. 😅
Once you’ve worked out your timing, you’re almost ready to go. The last thing to consider is each plant's growth habit.
Some flowers, like calendula, grow very quickly. If you start them too early, you’ll end up with oversized transplants that have already outgrown their pots and won’t perform as well once planted in the garden.
Most Sweet William are biennials and need to be planted a year before (and have a cold period over winter) they will flower. This is a bucket of Sweet William 'Amazon Rose Magic,' a first-year-flowering cultivar.
Some of my top 'cool flowers' that I start as transplants
| Flower | Favorite Variety | # weeks before planting out to start indoors |
| Snapdragon | Chantilly Lt Salmon, Maryland Appleblossom, Madamme Butterfly Broze, Potomac Lt Orange | 6-8 |
| Icelandic Poppy | Colibri | 6-8 |
| Sweet William* (first year flowering varieties) | Amazon and Sweet Series | 6-8 |
| Foxglove* (first year flowering varieties) | Camelot and Dalmation | 6-8 |
| Rudbeckia | Indian Summer, Cherokee Sunset, Sahara |
6-8 |
| Feverfew | Magic Single | 6-8 |
| Monarda | Lambada | 6-8 |
| Scabiosa Atropurpurea (annual) | Blue Cockade, Black Knight | 6-8 |
| Strawflower | Apricot, Silver Rose | 6 |
| Calendula | Ivory Princess, Orange Prince | 4 |
A field of blooming Calendula! We grow varieties such as Ivory Princess and Orange Prince. These types grow stocky, tall stems with very full blooms, which make them superior for cutting.
Before You Plant: Harden Off Your Seedlings
Even though these plants are cold-hardy, they’ll still be more tender after spending their early life indoors. Before planting them out, be sure to harden them off.
Hardening off is the process of slowly introducing young plants to the outside world so they can adjust to sun, wind, and fluctuating temperatures. Start by placing them outdoors in a protected spot for a few hours each day, then bring them back in before dark. Gradually increase both their sun exposure and the amount of time they spend outside over at least three days.
Once planted, these cool flowers can usually handle light frosts. We still like to keep frost cloth on hand just in case. Since we grow flowers commercially, we want to make sure our crop looks its best and shows no signs of damage. In a home garden, though, there’s usually no need to worry too much over a light frost.
Starting hardy annuals indoors does take a little more planning, but for us, it’s well worth it. A bit of extra effort early in the season means earlier blooms, fuller beds, and a lot more colour in the garden when spring is still just getting started.
