For many of us home gardeners, there’s nothing quite like the satisfaction of growing a plant from a tiny seed. If you’re looking for an easy win, Cosmos (also known as Mexican Asters) are the perfect choice. While they are simple to grow, starting your Cosmos seeds indoors is the best way to get a head start on those beautiful blooms.
How to Start Cosmos Seeds Indoors
Starting edible Cosmos indoors is a breeze, making it a fantastic project for gardening newbies. For your soil, you’ll want to use a low-nutrient seed-starting mix, or you can DIY it by mixing standard potting soil with a bit of sand. The sweet spot for sowing your seeds is during March and April. A sunny windowsill or a warm greenhouse works perfectly—just try to keep their environment consistent. Here’s what they need:
- Temperatures of at least 70°F (20°C)
- Consistently moist soil
- Good drainage (no soggy feet!)
When planting, only cover the seeds with a very thin layer of soil. Pro tip: Use a spray bottle to water them so you don’t accidentally wash away the seeds or the dirt. You should see little sprouts popping up in about 2 to 3 weeks. Once your seedlings hit about 3 inches tall, it’s time to prick them out and move them to their own small pots.
Moving Your Cosmos Outdoors
Before you move your Cosmos into the full sun of your garden, you’ll need to “harden them off.” Start by putting them outside in the sun for short bursts, gradually increasing the time each day. This helps them get used to the direct UV rays and prevents their delicate leaves from getting scorched. Since Cosmos are not frost-hardy, make sure to wait until the danger of frost has completely passed before planting them in the ground.
Saving Your Cosmos Seeds
One of the coolest things about Cosmos is how easily they self-seed. If you want to take the lead, you can harvest the seeds yourself after the flowering season to use next year. Just make sure the seeds are completely dry and store them in a cool, dark place. Keep in mind, though, that Cosmos seeds aren’t “true to type.” This means the new plants might look a little different from the parent plant—you might even get a fun surprise with a new flower color!
