Iris hollandica, commonly known as Dutch iris, is a species of flowering bulb that blooms for a few weeks in April or May. Blue and blue-purple flowers are among the most common flowers, along with yellow, white and bi-colored blooms. Growing the bulbs is fairly straightforward to do, provided you select an appropriate planting location and offer basic care as the bulbs establish themselves.
Select a location for your iris bulbs where they will receive full sunlight. Plant the bulbs in the autumn and set them into holes about 5 inches deep. Space the bulbs 4 to 6 inches apart or plant up to eight bulbs per square foot. Bulbs range in size from 3 to about 5 inches in circumference. If you plant in a container, use potting soil with a balanced mix of soil, peat moss and perlite. Plant the bulb so you have at least 1 to 2 inches of soil between the bulb and the bottom of the container. The Dutch iris is an annual, so you'll need to plant new bulbs each season.
Iris hollandica grows well in climates as cold as USDA Hardiness Zones 9 to 10. If you cover the ground with mulch, the bulbs can survive in Zone 8, as well. Keep the soil well-watered throughout the springtime growing season but not water-logged. Expect blooms once the shoots reach heights of about 6 inches, though the plant may reach an overall height of 20 inches.
To thrive, the Iris hollandica requires a cycle of very warm, cool and warm temperatures. The first stage should be 75 to 85 degrees Fahrenheit, the second should be 35 to 50 degrees, and the final warm stage should range between 50 and 60 degrees. In most locations, this corresponds to the summer, winter and spring. If you want to grow the flowers indoors in a container, you can simulate the changes in temperature by using a refrigerator to mimic cold winter temperatures. Instead of waiting until spring, you can force your iris to bloom indoors in early winter.
If you want to plant an assortment of flowering herbs alongside your iris, good companion plants include lavender, echinacea and pittosporum. For a grouping of flowering bulbs, crocuses, daffodils, hyacinths and tulips are all spring-blooming. In addition, they all respond well to forced indoor blooming should you wish to grow an indoor flower bed. However, when arranging cut flowers, avoid putting irises in the same vase with daffodils, as mucilage from the daffodil stems can interfere with the irises' blooming.
- North Carolina State University Cooperative Extension: Iris Hollandica
- Clemson University Cooperative Extension: Spring-Flowering Bulbs
- Clemson University Cooperative Extension: Forcing Bulbs Indoors
- National Center for Biotechnology Information: Phytochemistry -- Daffodil Flowers Delay Senescence in Cut Iris Flowers;