Easy Steps To Plant Cosmos Seeds, Indoors and Out

cosmos seedlings in plastic pots

Getting seeds started in the spring is a surefire way to shake off winter and look forward to the growing season. If you’re new to starting your own seeds, then cosmos are an easy way to get started. Cosmos seeds are cheap, with a packet of 50 seeds usually costing just a few dollars, and the planting process is very straightforward.

Start cosmos seeds indoors 4-6 weeks before your last spring frost in seed trays, then transplant them into the garden once the risk of frost has passed. To direct sow cosmos seeds, scatter the seeds lightly over the garden bed, and they will sprout in 7-14 days.

With either method, you’ll soon have tall cosmos plants waving in the breeze and handfuls of flowers ready for the vase.

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Planting Cosmos Seeds

You can choose to start seeds early indoors or wait a bit and plant them directly in the garden. Starting indoors will pay off with earlier blooms, but planting them in the garden will simplify your spring season since you don’t have to tend to seedlings indoors or have a setup for your seed trays.

Choose the method that makes sense to you, and in just a week or two, you’ll have cosmos seeds sprouting.

If you don’t have seeds yet, many fantastic seed companies online offer dozens of cosmos varieties. If you need some online seed companies to check out, here’s an article with some of my favorites: 10 Best Places To Buy Quality Flower Seeds Online

Starting cosmos seeds indoors

To start cosmos from seed indoors, you need just a few supplies. The process is similar for almost all seeds, so you may already have some of these supplies on hand.

  • Seed trays or old plastic containers such as milk jugs, paper cups. or deli containers. make sure whatever you use has some drainage holes to let out excess water.
  • Seed starting mix made of compost, perlite, and vermiculite. This type of mix is light, fluffy, and holds moisture well. You can buy bags of pre-made seed starting mix, or make your own. Garden Betty has a great article showing you how to make your own mix with an easy recipe.
  • Seeds! I like to buy my seeds from Johnny’s Selected Seeds and Baker Creek Heirloom Seeds.

I’ll describe all the steps, but if you prefer to watch a video, check out this complete tutorial from Danielle at Northlawn Flower Farm.

  • Make sure the seed starting mix is pre-moistened, or mix in some water so it’s wet but not saturated. If you squeeze a handful of the mix, it should stick together but not drip water.
  • Fill the seed trays, cups, or whatever container you are using. Gently press the soil into the container.
  • Grab your seed packet, and place one seed per tray cell on the soil. If you’re using old food containers that aren’t neatly divided, then place a seed every 1-2 inches on the soil surface.
  • Cover the seeds with another quarter inch of seed starting mix, then pat it into place over the seeds.
  • Mist the soil to settle the seeds in place. Don’t water the soil directly with a watering can. The flow is too strong for brand new seeds.
  • When the soil needs to be watered more heavily, bottom water by setting the container in a dish or pan of water for several minutes. The seed-starting mix will wick water up through the drainage holes.
  • Place the seed trays or containers under a row of shop lights, with the light just two inches above the soil.
  • If you don’t have a light set up, then make sure to put your seedling tray in the sunniest possible location to make sure they don’t get leggy, or overly long, as they reach for the light.
  • If you’re starting seeds in the garage or a cold area, consider a heat mat to warm the soil.
  • Mist the seed trays with a spray bottle once or twice a day to keep the seeds moist while they germinate, and you should see sprouts within a week or two.

You will need to tend to your seedlings every day for the next 4-6 weeks to keep the soil watered and to monitor the lights, raising them as the plants grow taller. The lights should be about two inches above the plants to keep the light strong but still give them room to grow.

Direct sowing cosmos in the garden

If you prefer to sow cosmos seeds directly in the garden, then your planting process is a snap. Here’s a helpful video from Beautiful Nest Home & Garden, with the steps below:


The steps for direct sowing cosmos seeds.

  • Once the soil has warmed up in the spring, clear the growing area of any weeds or debris so the seeds can make good contact with the soil.
  • Rough up the soil surface by scratching it with a rake or your hand. This creates a loose surface that holds the seeds in place.
  • Lightly scatter the seeds over the soil so that a seed lands every few inches or so. You need enough seeds to account for the ones that won’t germinate, but you don’t want so many that they overcrowd each other. If they all sprout, you can thin them out later.
  • Once the seed is down, cover them lightly with about a quarter inch of soil, then press your hand over the soil to make firm contact with the seeds.
  • Use a watering can or hose with a gentle stream to water the seeds.
  • Keep the seedbed moist until the seeds start to germinate in 7-14 days.

If you need a list of other flowers that are easy to start from seed, I have a list of some of my favorites in this post, 10 Easy Cut Flowers To Grow From Seed: With Seed Photos

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