Learn Growing Cosmos in Pots in this detailed post and include the colorful, daisy-like blooms in your plant collection.
Cosmos (Cosmos sulphureus) are easy-to-grow flowering annuals; these classic cottage garden blooms attain full maturity in around two months. They germinate slowly but flower rapidly after that and continue to blossom over the fall. The colorful blooms in white, pink, golden yellow, orange, yellow, red, magenta, and chocolate hues resemble daisies that bees, birds, and butterflies love. Leaves are pinnate, bipinnate, or lobed, opposite on stems. If you want to include the cosmos and those living in the Southern U.S., grow the cosmos in pots as they are invasive.
Botanical Name: Cosmos sulphureus, Cosmos bipinnatus
Common Names: Cosmos, Cut-leaf cosmos, Mexican aster
USDA Zones: 2-11
Native Place: Central America, and northern South America, southern North America
Propagating Cosmos
Cosmos are self-seeding plants propagating them after the danger of frost has gone. Growing from seeds is the easiest method, but you can plant cosmos through stem cuttings as well. Follow the steps below:
Fill a 3-inch pot with moist potting mix, and make a 1-2 inches deep shallow hole in the soil with a pencil tip. Check for a cosmos shoot with 3-5 leaf nodes on the stem; use sterile pruning shears, cut under the last leaf node, and remove leaves.
Insert the stem into the hole in the container, and ensure the last leaf node remains above the soil line. Pack the soil around the stem. Keep the soil moist; you can see new growth in three weeks.
How to Grow Cosmos From Seeds
You can start seeds indoors 4-6 weeks before the last frost or sow the seeds directly in the garden after the threat of frost is gone. Don’t rush, as the cosmos grows fast and can be killed by a late frost. The seeds germinate in 7-21 days at 75 F, and flowers appear in about 50-60 days.
Loosen the soil to 8-inches depth, sow the seeds and cover them with 1/4 inch of soil. Space the seeds as mentioned in the packet. Thin out the plants and move extra ones to another part of the garden.
Why Select Container Growing?
If you don’t have enough space or your own yard, containers are a good option to grow cosmos plants. In limited spaces where growing food crop is necessary, they can be potted and kept near those plants for better pollination.
Potted cosmos can be easily moved to a sheltered area for improved protection from cold when the temperatures drop below 40 F. Similarly, for better flowering, you can transfer containers to sunny locations on the porch or patio.
Cosmos plants are quite drought resistant and heat-loving; their roots also grow deeper; keeping in mind that, choose a 12 inches deep and wide pot with drainage holes. Avoid using plastic or resin containers as they keep moisture for a long time, which can cause root rot and pathogens.
Ideal Growing Conditions for Cosmos in Pots
Light
Select an area that receives full sun for profuse blooming; you can grow it in partial shade but will have fewer blooms. Cosmos can thrive in the hottest conditions like indigenous surroundings, the dry regions of Mexico, and Central America.
Soil
Cosmos favors neutral soil with a pH of 6.0-8.0, though it can also be planted in poor soil. It thrives well in medium moisture, well-draining soil but performs appropriately in dry soil. Do not plant in rich soil; it can make the plant tall and flip over.
Water
When the cosmos are mature enough, they will not require water unless there is an extended drought. Check the soil daily in high heat; if the top two inches feel dry to the touch, water the plant deeply.
Temperature and Humidity
Cosmos prefer hot weather. They flourish at any level of humidity.
Cosmos Care in Pots
Fertilizer
Cosmos can manage in poor soil; hence feeding can negatively affect the plant. Excess fertilizer can lead to sturdy plants with no blooms and too many leaves. If your cosmos is struggling, then it’s to feed it.
Pruning
Cosmos plants are herbaceous and do not require pruning; the main stems are fairly woody. Remember that some cultivars can grow up to 5 feet in height, so if you are concerned about it, select a dwarf or compact variety. However, regular trimming promotes the growth of new buds.
Deadheading has to be done regularly if you are not planning to collect seeds for planting the next season.
Overwintering
Perennial varieties require some winter protection in areas where winter frequently dips below 40 F. Move the pots to a sheltered area and cover the pots with burlap or bubble wrap for extra protection. The perennial varieties flower until mid-to-late fall in areas that have cold winters. Trim the dead stems back to the rhizome after the last blossom shriveled and, wrap the container, transfer to the garage or sheltered area.
For annuals, if you let them self-seeds in pots, move the plants to a basement for winters and bring them back when spring spins around.
Repotting
Repotting is not essential with annual except you begin with small pots. Perennials require repotting periodically to keep sufficient root space.
For repotting, fill the sterile pot with fresh potting mix in the base to elevate the root system. Check the roots to ensure there is no rot, and put the root ball into a new container filled with fresh soil. Water well and place in a sunny area.
Pests and Diseases
Pests or diseases hardly impact the potted cosmos. Though spider mites, aphids, and thrips can affect the plant. Thankfully, they are also deer resistant.
Diseases rarely occur, but powdery mildew and aster yellow can interfere. Smut can become a problem as well.
The cure for aster yellow is prevention. Sufficient airflow around plants controls powdery mildew. Remove the infected foliage and dispose of them to stop the spread. Smut can be prevented by proper spacing and watering at the base of the plant.
Best Cosmos Varieties
Cosmos Species
C. Bipinnatus
It features thread-like foliage that is fine, dainty, and wispy. Generally known as ‘tall cosmos’ or ‘garden cosmos’. The flowers open in red, purple, pale yellow, and white shades with yellow centers.
C. Sulphureus
Commonly known as the ‘sulfur cosmos,’ the blooms resemble marigolds. This drought tolerant variety grows up to three feet tall.
C. Atrosanguineus
Native to northeast Mexico, this species is also popular as the chocolate cosmos. The blooms emerge on wiry stems in deep red to chocolate maroon with a matching center. They release a chocolaty fragrance and grow up to 30 inches tall and 18 inches wide.
Types of Cosmos for Growing in Pots
1. Candystripe
It features bicolored petals with crimson edges, red-pink strips, and yellow centers.
2. Choca Mocha
This atrosanguineus cultivar offers flowers in deep brown-red color with dark centers.
3. Bright Lights
It sports a mix of yellow, red, and orange hues in blooms.
4. Apricot Lemonade
This bipinnatus cultivar displays apricot-shade blooms with a lilac blush that slowly fades to a buttery yellow with pink hints.
5. ‘Sea Shell’ Series
It flaunts a blend of pastel hues in unique tubular petals.
6. Cosmic Orange
It produces semi-double orange blooms that are drought tolerant.
7. Peppermint Candy
This award-winning cultivar shows off petals in magenta and white hues.
8. LadyBird
This short cultivar opens in red, orange, yellow, or gold blooms that grow up to 18-24 inches tall.
9. Cupcake White
The 4-5 inch white blooms have a yellow center with tufted petals.
10. Daydream
It produces dark pink blossoms that fade to pale pink and yellow centers.
