Key Points
Take a quick garden walk to spot watering or pruning needs.Don’t panic—most stressed plants can bounce back with care.Check for pests that may have moved in while you were away.
Unfussy cosmos are a low-maintenance landscaper lover’s dream. They don’t need much help to produce a profusion of colorful, pollinator-friendly blooms. However, if you’re growing cosmos and they’re only producing a few flowers or they suddenly stop blooming in the height of summer, you might be making some simple mistakes in terms of care or conditions.
Here’s how to make your cosmos bloom again (and again) right through summer to the first fall frost.
Why Cosmos Stop Blooming in Late Summer
Various culprits could be causing your cosmos flowers to fade or fail to rebloom as summer progresses. Aside from not tidying spent flowers, neglecting to adjust your care to account for seasonal changes can be a blight on blooms.
Too much shade, excessive fertilizer or water, and lack of respite from intense heat waves can all slow down or stop cosmos from blooming.
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7 Ways to Make Cosmos Bloom Again
To ensure your cosmos have a second wind when it comes to flowering, try these tricks.
Deadhead spent flowers: When the first flush of flowers fades, cut the stem with sterile shears above the first leaves to promote new bud formation. This keeps your plant focused on flower production.
Pick the best yard position: Cosmos are sun-lovers that need a minimum of 6 to 8 hours of full sun to produce plenty of big blooms.
Protect during heatwaves: Temperatures above 95°F will stress your cosmos and pause blooming. If you live in a heatwave-prone region, consider growing cosmos in containers. That way, you can move them to a cooler when the mercury rises.
Pinch for productive plants: When your young cosmos reach 8 to 10 inches tall, use clippers to remove the top of the stem, leaving just a few sets of leaves. This encourages more branches and blooms.
Weigh up your watering habits: Cosmos are drought-tolerant plants that don’t appreciate soggy soils. Avoid overwatering, letting the soil dry fully between irrigations.
Avoid overfertilization: These plants thrive in poor soils and don’t require feeding when grown in the ground. A balanced, slow-release, low-nitrogen fertilizer is best for container-grown cosmos. Too much nitrogen means the plant will focus on leaf rather than bloom production.
Prune to promote air circulation: Fungal diseases, like fusarium wilt and powdery mildew, can cause problems with cosmos bud drop and bloom development. Don’t plant seedlings too close, prune vigorously branching leaves, and water plants at the base.
Avoid artificial light: If you have security lights on all night in your yard, this can cause issues as cosmos need 12 hours of darkness to start blooming.
3 Signs Your Cosmos Will Rebloom
After taking steps to remedy an unexpected pause in blooming, these subtle clues could be a sign that a flurry of fresh flowers are on the way.
New bud formation: Can you see new, small, round swellings at the tips of your plant’s stems? This means that new blooms are forming.Fresh growth: Stressed plants stop or slow their leaf production and can experience stunted growth. If you see signs of new leaves growing and your plant is putting on a growth spurt, that’s a good sign.Plant perks up: A wilting plant that has too much sun or the wrong amount of water will start to become more upright as it recovers its vigor.
How to Keep Cosmos Blooming Until Frost
Now that you’ve got the blooms back on track, continue to make the most of the flowers until the first frosts arrive by watering deeply but infrequently, allowing the soil to dry out in between waterings.
Watch for pests, such as aphids, slugs, and spider mites, to proactively prevent bloom-limiting infestations. Plus, provide shelter from strong winds to help protect tall cosmos varieties when staking isn’t enough.
FAQ
What kind of fertilizer encourages cosmos to rebloom?
For cosmos growing in containers, you can use a slow-release, balanced fertilizer that is low in nitrogen. Nitrogen focuses on foliage growth at the expense of flower development. However, most cosmos plants grown in the ground won’t need additional nutrients. These plants thrive on neglect and do well in poor soil.
Can cosmos survive light frost?
Cosmos are annuals that typically die back once the first frost hits. Chocolate cosmos is a tender perennial. However, it’s also best to grow this variety in containers. That means you can move the plants indoors or into a greenhouse, or store the tubers before any frost arrives.
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