Not every sunflower is a perennial that can shrug off a deep freeze. In fact, many of our favorite varieties have to be replanted every single year. It’s a bit of a balancing act: if you start them too late, you’ll be waiting forever for those iconic yellow blooms, but if you put them out too early, a late frost will take them right out.
Wait Until Mid-May for Outdoor Safety
Whether you’ve got a tiny sprout or a plant that’s already gained some height, keep this in mind: annual sunflowers (Helianthus annuus) are definitely not cold-hardy. Since temperatures can still dip below freezing through mid-May (what we gardeners often call the “Ice Saints”), you should wait until after that danger zone to move your sunflowers outside. If you’re sowing seeds directly into your garden beds, you can usually start around late April.
Since annuals don’t really start their outdoor growth spurt until mid-May, it takes a little patience before they hit their peak blooming season. That’s why I always recommend starting them indoors to get a head start.
Sowing Directly in the Garden
If you’re planting seeds directly in the ground, wait until late April. Even if spring gives us a few gorgeous, warm days early on, the soil takes a lot longer to warm up. Don’t let a sunny afternoon trick you into planting too soon!
Pro Tip:
Instead of just dropping seeds in the dirt, you can pre-germinate them indoors and transplant the mini-seedlings in mid-May. This is a total game-changer because birds love to snack on unsprouted seeds, but they usually leave the little green starts alone.
Starting Sunflowers Indoors
Once the days start getting longer in early March, you can start growing your sunflowers inside where it’s nice and toasty. Here’s how to do it:
- Fill a seed tray or small pots with seed-starting mix or potting soil.
- Poke the seeds about 1 inch (2 cm) deep into the soil.
- Plant 3–5 seeds together, leaving about 2 inches (5 cm) between clusters.
- Keep the soil consistently moist.
- Place the pots in a bright, warm spot.
- Once they sprout, pick the strongest seedling in each group.
- Snip off the weaker ones so they don’t compete.
- Repot them if they outgrow their starter containers.
- Water daily and fertilize weekly.
When to Move Your Young Plants Outside
By mid-May, both store-bought and home-grown sunflowers are ready for a sunny spot in the garden. Before they move out for good, it’s a smart move to “harden them off”—put them outside for a few hours at a time on nice days to get them used to the direct sun.
You can also grow sunflowers in containers. Dwarf varieties are especially perfect for balcony gardening.
If late April or early May is looking unusually warm and the forecast is clear, you can take a gamble and plant them a little early. Just keep a close eye on the weather! Be ready to cover them up or bring pots back inside if a surprise frost heads your way.
