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Cosmos Seeds, Rubenza
Description
(Cosmos bipinnatus). This deep, rich, ruby-red color is very unusual in a cosmos! The single blooms open a luxuriant burgundy and mature to a faded rose. Contrasting burnished gold centers are striking and regal! The compact plants only reach 24” high. Like all cosmos, these are superb for cutting!
- Annual
- 60-90 days to maturity
- 6-8 hours of full sun
- Sprouts in 7-14 days
- Seed Depth: 1/8-1/4"
- Plant Spacing: 10"
- Ideal Temperature: 70-75 F
- Frost Hardy: No
Growing Tips, Tricks and FAQs
Growing Tips
Rubenza cosmos is a stunning easy-to-grow annual. These plants prefer full sun and poor or moderate soil, as excessively rich soil leads to lots of foliage and fewer blooms. Regular deadheading will prolong blooming from midsummer until the first frost.
When to Grow
Sow cosmos seeds after the last frost, once the soil has warmed to at least 60 F. In areas with short growing seasons, start seeds indoors 3-4 weeks before the last frost and transplant them once outdoor temperatures are consistently warm. In milder climates, cosmos can be direct sown in late spring or early summer. For the best planting time, check your region’s last frost date before sowing. If you’re unsure how to do that, check out our blog post ‘Our Experts Answer Questions, Share Resources.’
How to Sow and Plant
After the danger of frost has passed, scatter seeds directly onto light, well-draining soil. Press them lightly into the surface at a depth of 1/8-1/4 inch, as cosmos seeds need light to germinate. Space plants around 10 inches apart so that they have enough room for healthy growth. Keep the soil evenly moist until seedlings emerge, usually within 7-14 days. If starting indoors, choose a light, well-draining seed-starting mix. Maintain a temperature of 70-75 F for best germination. Harden off seedlings before transplanting them outdoors to prevent transplant shock.
How to Grow
Make sure that the plants receive at least 6-8 hours of direct sunlight daily for the richest color and most blooms. Once established, Rubenza cosmos is drought tolerant and requires only occasional watering. Avoid overwatering, as it can weaken the plant. Taller plants may need staking, especially in windy locations. If plants become too leggy, cut them back by one-third to encourage bushier growth.
How to Save
- Cosmos are insect pollinated, and there may be some crossing between varieties in the garden. You can enjoy the mixing or use caging techniques and hand pollination to avoid crossing.
- Saving seeds from cosmos is easy: simply allow the heads to brown and dry on plants and collect seeds. Store in a cool, dry, dark place over winter.
FAQ
How can I encourage the Rubenza cosmos to bloom more?
Remove spent blooms to prolong the blooming season. Additionally, you can trim back leggy plants by one-third mid-season for bushier growth and more flowers.
Is the Rubenza cosmos resistant to pests and diseases?
Cosmos are generally pest-resistant, but they may occasionally attract aphids or spider mites. Space the plants properly and avoid overwatering to help prevent fungal issues.
Will the Rubenza cosmos self-seed for next year?
Yes, if flowers are left to go to seed, cosmos may self-sow, allowing new plants to emerge the following season in mild climates.
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