Cosmos

Cosmos bipinnatus · Flower

Quick answer: Water: Every 7–10 days in dry spells (estimated); drought tolerant once settled; about 1 in every 1–2 weeks (estimated). Light: Full sun, at least 6 hours. Soil: Poor to average, well-drained, pH 6.0–8.0. Pets: The ASPCA plant list has no separate entry for Cosmos, and it is not generally known as toxic to cats and dogs. Eating a lot of any plant can still upset the stomach. If in doubt, ask your vet.

A light, airy annual with feathery leaves and simple daisy-like flowers. It actually prefers poor soil and little care. Bees and butterflies love it, and it often reseeds itself for next year.

Care at a glance

Light

Full sun, at least 6 hours

Water

Drought tolerant once settled; about 1 in every 1–2 weeks (estimated)

Soil

Poor to average, well-drained, pH 6.0–8.0

Temperature

Best 65–85 °F (estimated); frost tender

Spacing

12–18 in apart (estimated)

Container

10–12 in deep, 2 gallons

Bloom

7–10 weeks after sowing until frost (estimated)

Lifespan

Annual; often self-seeds

When?

Sow outdoors after your last frost when the soil has warmed, or start indoors 4–6 weeks earlier. In mild areas this is usually late April to May; in colder areas late May (estimated).

Step by step

1. Sow seeds 1/4 in deep; they sprout in 7–10 days (estimated).
2. Thin seedlings to about 12 in apart.
3. Pinch the tips once plants are 12 in tall for a bushier shape.
4. Skip most fertilizer; rich soil makes tall, floppy stems with few flowers.
5. Stake tall varieties in windy spots.
6. Remove faded flowers regularly; leave the last ones to drop seed for next year.

Common problems

Pets

The ASPCA plant list has no separate entry for Cosmos, and it is not generally known as toxic to cats and dogs. Eating a lot of any plant can still upset the stomach. If in doubt, ask your vet.

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