Growing Cosmos from Seed

Once upon a time, back when gardeners planted seeds, nurtured seedlings and watched them grow into stunning beauties, 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.

"Before planting, Shepherd has one rule: read the directions carefully. One packet says to sow 1/2-inch deep and an inch or two apart in a sunny location with well-worked soil, but directions vary. She has two sowing methods with the first using a one-by-one stick or ruler.

First she slides the stick across the soil to form a shallow trench and plants according to the packet instructions. 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.

More relaxed gardeners can choose a less fussy planting method. Just shake, scatter and sow. Rub soil between your fingers over the seeds to cover them evenly. "Even if a few are too close or too far apart, we're going to have a nice bed of cosmos," she says. Don't worry if plants grow close together. You can thin them later, according to the instructions on your packet.

Cosmos are adaptable to almost any kind of soil, but they do need moisture to germinate. In dry, hot climates, Shepherd recommends placing a shade cloth over the bed until the seedlings begin to sprout. This happens roughly five to 10 days after planting.

"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."

Cosmos blooms continuously until the first frost. With its distinguished forms and vibrant colors, it's no wonder why so many gardeners are over the moon for cosmos, even those with small yards.

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

While compact Cosmos sulphureus are great for containers, Cosmos bipinnatus reaches six feet or higher with a tendency to topple over. Fortunately, Shepherd has a way to keep them from drooping. She has created a low-maintenance cosmos support system from garden netting attached to wood stakes. These stakes secure to notched metal posts that stretch over the entire bed. As the plants grow, the netting practically disappears.

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.