By Jackie Carroll
If you’re looking for container plants loaded with pretty blossoms throughout summer and well into fall, cosmos is a great choice. Growing cosmos in pots is easy, and you’ll be rewarded with plenty of flowers for cut or dried arrangements, or you can simply enjoy them in their pot. Keep reading to learn more about container grown cosmos.
Container Grown Cosmos
Cosmos flowers can be successfully grown in containers. Species plants can grow as much as 6 feet tall, so look for dwarf or compact cultivars for containers.
Of the 20 species of annual and perennial cosmos flowers, cultivars of C. sulphureus and C. bipinnatus are best suited to containers. C. sulphureus comes in shades of yellow, orange and red, while C. bipinnatus blooms in pink and rose tones.
Can Cosmos be Grown in Containers of Soil from the Garden?
Two things happen when you fill a container with regular garden soil. First, it compacts, making it hard for water to drain and for air to get to the roots. Second, it pulls away from the sides of the pot so that water runs down the side of the pot and out the drainage holes without moistening the soil.
A general-purpose potting medium manages water efficiently, and most commercial potting mixes include enough slow-release fertilizer to feed the plant for the first half of the season.
If you prefer, you can make your own potting medium. Mix equal parts of good garden soil, peat moss and either vermiculite or perlite. Add some slow-release fertilizer and fill the pot.
How to Grow Cosmos in a Pot
Choose a pot at least 12 inches in diameter with several drainage holes in the bottom. Heavy pots are stable and can help prevent the plant from toppling. If you use a lightweight plastic pot, place a layer of gravel in the bottom of the pot to add weight before filling it with potting mix.
Scatter the seeds thinly over the surface of the potting soil and cover them with one-third to one-half inch of additional soil. When the seedlings are 4 inches tall, thin the plants by clipping out the unwanted seedlings with scissors. Container-grown cosmos looks best when you thin the plants to about half the distance recommended on the seed packet. When your seedlings are off to a good start, set the pot in a sunny location.
Water container-grown cosmos when the soil is dry to a depth of two inches. Drench the soil and then allow the excess water to drain through. After about 20 minutes, empty the saucer under the pot. Cosmos doesn’t like excess moisture and the roots may rot if the pot is left sitting in a saucer of water. Pots that sit in sunny locations dry out quickly, so check the soil moisture daily.
Cosmos plants react to rich, fertile soil or an abundance of fertilizer by growing tall and leggy. When growing cosmos in pots, a light feeding with slow-release fertilizer lasts through the entire season. If you prefer, you can use a liquid fertilizer mixed at one-quarter strength once every week or two. If the plants start to look lanky, cut back on the amount of fertilizer.
Pinch off dried leaves and faded flowers to keep the pot looking neat. Regular deadheading encourages the plant to produce more blossoms. If the stems become leggy with few flowers in mid-summer, cut them down to about one-third of their height and let them regrow.