Growing cosmos is a total breeze, and honestly, it’s one of the most rewarding flowers for any gardener. Whether you start them indoors or sow them directly in your garden, you’ll see results fast. There’s nothing quite like watching these “Mexican Asters” take off from tiny seeds to beautiful blooms!
Where to get your cosmos seeds
You can easily pick up a packet of seeds at your local garden center or order them online. Now, if you’ve grown cosmos before, you might be tempted to save the seeds from your own plants. While those seeds will definitely sprout, they usually aren’t “true to seed.” This means the new flowers might look a little different in color or height than the parent plant—but hey, sometimes a little garden surprise is fun!
Starting cosmos on your windowsill
If you want a head start on the season, starting your edible cosmos indoors is the way to go. This process, known as pre-cultivation, also works great in a greenhouse. Since cosmos aren’t winter hardy, they really need a cozy temperature of around 68°F (20°C) to wake up and germinate.
You can get started as early as March or April. Here’s what you’ll need:
- A low-nutrient seed-starting mix, or
- Standard potting soil mixed with a bit of sand.
Just barely cover the seeds with a thin dusting of soil. Give them a gentle misting with a spray bottle to keep things damp but not soaked. Keep that soil consistently moist, and in about two to three weeks, you’ll see those cute little sprouts popping up.
Sowing cosmos directly in the garden
If you’d rather skip the seed trays, you can sow them straight into the ground. Just make sure to wait until after the last frost (usually mid-May) so the tender seedlings don’t get nipped by the cold. Keep in mind that direct-sown flowers will bloom a few weeks later than those started indoors. Use a light, sandy soil mix if you can, and make sure the patch stays evenly moist while they’re getting established.
One cool thing about cosmos? Even though the plants themselves won’t survive the winter, the seeds they drop are tough as nails. They’ll often “self-seed” and pop up all on their own next spring. If they happen to sprout in a spot where you didn’t want them, don’t worry—they handle being transplanted like champs!
