Cornflower
Centaurea cyanus
Classic wildflower with intense blue blooms that attract bees and butterflies. Edible petals make a striking garnish.
Overview
Companion Planting
Cosmos
ZinniaToxicity
Listed as non-toxic by the ASPCA for dogs, cats, and horses. Petals are edible for humans and commonly used as a garnish and in herbal teas.
Planting Tips
1 cm of water per m² equals 10 liters. Use the Watering Calculator for exact amounts.
Care Tip: Deadhead spent blooms regularly to prolong flowering. Thin seedlings to 20-25 cm apart for good airflow. Tall varieties may need staking in windy sites.
Common Pests
Aphids
Symptoms: Clusters of small green or black insects on stems and buds; curled or distorted new growth; sticky honeydew residue and sooty mold.
Treatment: Dislodge with a strong water spray; apply insecticidal soap or neem oil if infestation persists.
Prevention: Encourage natural predators such as ladybugs and lacewings; avoid excessive nitrogen fertilization that promotes soft growth.
Leaf Miners
Symptoms: Winding, pale tunnels or blotch mines visible within leaves; affected leaves may yellow and drop prematurely.
Treatment: Remove and destroy mined leaves promptly; apply neem oil or spinosad for heavy infestations.
Prevention: Use floating row covers early in the season; remove plant debris in autumn to eliminate overwintering pupae.
Spider Mites
Symptoms: Fine stippling or bronzing on leaves; tiny webbing on leaf undersides; leaves dry out and drop in severe cases.
Treatment: Spray foliage with a strong jet of water; apply horticultural oil or miticide if populations are high.
Prevention: Maintain adequate moisture around plants (mites thrive in hot, dry conditions); avoid broad-spectrum insecticides that kill mite predators.
Common Diseases
Powdery Mildew
Symptoms: White, powdery coating on leaves, stems, and buds; affected leaves may yellow, curl, and drop.
Treatment: Remove heavily affected foliage; apply sulfur-based or potassium bicarbonate fungicide. Neem oil can also help in early stages.
Prevention: Ensure good air circulation by spacing plants adequately; water at soil level rather than overhead; choose resistant varieties when available.
Rust
Symptoms: Orange-brown pustules on leaf undersides; yellow spots on upper leaf surfaces; premature leaf drop and weakened plants.
Treatment: Remove and destroy infected leaves immediately; apply a fungicide containing myclobutanil or sulfur.
Prevention: Avoid overhead watering; provide good air circulation; clear plant debris at end of season to reduce spore carry-over.
Gray Mold (Botrytis)
Symptoms: Fuzzy gray-brown mold on flowers, buds, and stems; affected tissue becomes soft and water-soaked, then turns brown.
Treatment: Remove and discard all affected plant parts; improve ventilation around plants. Apply a copper-based fungicide in persistent wet conditions.
Prevention: Avoid overcrowding plants; water at the base in the morning so foliage dries quickly; deadhead fading blooms promptly to eliminate infection sites.