Growing Cosmos from Seed

Cosmos are colorful flowers to enjoy for just a season, but a worthy visitor to any garden. Get tips for growing this popular annual from seed.


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If you're a gardener who thinks annuals aren't worth the effort because they're relatively short-lived, here's a flower that's out of this world. Derived from the Greek word meaning "beautiful," cosmos are as dainty as they are durable and are also one of the easiest plants to grow 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 flowers and container gardens, 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. 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.

Before planting, read the seed packet directions carefully. There are a couple of sowing methods. The first, slide a one-by-one stick or ruler across the soil to form a shallow trench and plants according to the instructions. Then pinch the soil over the seeds and applies lightly press it firmly in the ground. Finally, give the seeds a gentle drink of water.More relaxed gardeners can use the second, less fussy, planting method. Just shake, scatter and sow. Rub soil between your fingers over the seeds to cover them evenly.

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

Cosmos bloom 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 these flowers in their landscaping, even those with small yards.

Cosmos will only grow to about 21 to 22 inches, and they're perfect as part of your landscaping or container gardening. While compact Cosmos sulphureus are great for container gardening, Cosmos bipinnatus reaches six feet or higher with a tendency to topple over.

To keep your cosmos in bloom, keep them trimmed. Take a branch with many finished flowers, go a third of the way down the plant and cut. 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.

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