Iris bulbs should generally be planted about 4 to 6 inches (10 to 15 cm) deep to encourage reliable flowering the following year. For example, the Royal Horticultural Society recommends planting bulb irises up to 15 cm (6 inches) deep, spaced about 5-7.5 cm (2-3 inches) apart
. Dutch iris bulbs specifically are often planted about 4 inches (10 cm) deep and 2-4 inches apart
. For dwarf iris varieties like Iris reticulata, a slightly shallower depth of around 3 to 4 inches (7.5 to 10 cm) is appropriate, especially when planting in the fall
. When planting bearded irises, which grow from rhizomes rather than bulbs, the rhizome should be placed so the top is exposed or just barely covered by soil, rather than deeply buried
. In summary:
- Standard bulb irises: plant 10-15 cm (4-6 inches) deep
- Dwarf iris bulbs (e.g., Iris reticulata): plant 7.5-10 cm (3-4 inches) deep
- Bearded iris rhizomes: plant with tops exposed or just below soil surface
Ensure good drainage at the planting site to prevent bulb rot, and water well after planting
