How to grow iris
Overview
Iris germanica is a bearded iris grown from rhizomes, valued for its dramatic spring flowers and architectural foliage. It needs a pronounced dry rest after flowering to prevent rot and to set next season's buds.
Varieties
- Iris germanica 'Batik' — Striking purple-and-white striped flowers, very reliable in temperate gardens.
- Iris germanica 'Immortality' — Pure white, reblooms in autumn in mild climates; excellent for cutting.
- Iris germanica 'Superstition' — Deep near-black flowers, a dramatic choice for subtropical and temperate beds.
Soil Preparation
Iris prefers neutral to slightly alkaline soil (pH 6.8–7.5). Improve drainage by adding coarse sand or gravel to heavy soils. Work in a light dressing of lime or dolomite before planting if soil is acidic. Avoid fresh manure or high-nitrogen compost.
Growing Guide
Plant iris rhizomes in full sun with the top of the rhizome exposed at or just above soil level. Space 30–40 cm apart in well-drained, slightly alkaline soil. In heavy clay, plant on a slight mound or in raised beds. Avoid planting too deep — buried rhizomes rot quickly.
Care
Feed with a low-nitrogen fertiliser (e.g., 5-10-10) in early spring as growth begins, and again just after flowering. Remove spent flower stems at the base. In late autumn, cut back foliage to 15 cm to reduce rot risk. Divide rhizomes every 3–4 years in late summer to early autumn.
Companion Planting
Pair iris with low-growing perennials like lavender, catmint, or salvia that share similar sun and drainage needs. Avoid planting near vigorous groundcovers or moisture-loving plants that will shade or crowd the rhizomes.
Common Pests & Risks
Aphids cluster on new growth in spring — blast off with water or use insecticidal soap. Snails and slugs chew emerging leaves and flower buds; control with iron-based bait or hand picking. Rhizome rot (bacterial soft rot) is common in wet, poorly drained soil — dig out and discard affected sections.
Harvesting
Cut iris flower stems at the base as each bloom opens for longest vase life. Remove the entire stem after flowering to redirect energy to the rhizome. Do not harvest rhizomes for culinary use — they are toxic.
Troubleshooting
Yellow leaves: overwatering or poor drainage — reduce water and check rhizome for rot. Brown leaf tips: wind or salt burn — shield from strong coastal winds. No flowers: rhizome planted too deep or too much shade — lift and replant at soil level in full sun. Soft, mushy rhizome: bacterial rot — cut away affected tissue and dry in sun for a day before replanting. Leaves with brown spots: iris leaf spot fungus — improve air circulation and remove affected foliage in autumn.