The best time to plant iris bulbs is generally in the fall, from mid-August to mid-September, when overnight temperatures are between 40 and 50 degrees Fahrenheit (4-10 degrees Celsius). This timing allows the bulbs to establish roots before the winter and ensures optimal growth. Specific planting times can vary by hardiness zone:
- In cooler zones (e.g., zones 3 and 4), early August to early September is ideal.
- In moderate zones (e.g., zone 5 to 7), planting from September to October is best.
- In warmer zones (e.g., zones 8 to 10), planting can occur in October, November, or December.
For bulbous irises, planting in autumn is usual to meet dormancy requirements. In milder climates, some iris types may also be planted in early spring. Generally, it is important to avoid extreme heat for planting and ensure well- drained soil with adequate sun.
