Growing Cosmos from Seed

Once upon a time, back when gardeners planted seeds, nurtured seedlings and watched them grow into stunning beauties (figures A and B), cosmos swayed proudly in gardens across the land. Then along came the era of instant gratification with already-blooming plants in pots, and things that don't transplant well—like cosmos—fell from flowering favor.

But in true fairy-tale fashion where patience is a virtue and old things become new again, cosmos are enjoying a renaissance among seed-sowing gardeners. "Cosmos is one of those old-fashioned flowers that people remember from grandmothers' gardens," says garden expert Renee Shepherd. "They're easy to grow and fill the garden in nicely."

A prolific bloomer, cosmos transplants can grow much too large in tiny nursery pots and become root-bound. The easiest, cheapest and perhaps most satisfying solution is to plant a seed and watch it grow. "It's easy to start from seed," says Shepherd. "You'll get wonderful results, and from one little packet of seeds, you can have a whole yard full of plants."

First she slides the stick across the soil to form a shallow trench and plants according to the packet instructions (figure D). Then she pinches the soil over the seeds and applies the "Shepherd sowing secret," which is to assure good seed-to-soil contact by lightly pressing it firm. Finally, she gives the seeds a gentle drink of water.

"It's always such a thrill when little seeds produce lots and lots of young seedlings," says Shepherd, "but you really need to take out the extra seedlings just as the packet suggests. They'll really thrive and be more healthy if they have enough room to spread their roots."

"These shorter cosmos will only grow to about 21 to 22 inches, and they're perfect for growing in containers," says Shepherd (figure H). "They'll grow over a long season and are great for a patio, a fire escape or even a boat."

Here's one additional tip to keep your cosmos in bloom. "After your cosmos have their first flush of blooms, cut them back for another one," she says. To do this, take a branch with many finished flowers, go a third of the way down the plant and cut them off. Pruning is an easy way to prompt new growth and tidy up the plant. Afterward, fertilize, water and await a whole new crop.

As generous reseeders, you can either save the seed for next year's garden (remove the dried flower heads to get the seeds) or let nature scatter the seeds for you.