Colorado gardeners are so familiar with Bearded Irises (Iris germanica) that we tend to forget there are any others. It’s true that Bearded Irises do exceptionally well in our climate and soils, but they won’t bloom for several more months. Two smaller relatives—Iris reticulata and Iris danfordia—are blooming now. Why not grow them as well?
Iris reticulata and I. danfordia are collectively known as Dwarf Irises. You may also see them labeled miniature irises or rock garden irises. Iris danfordia is a sunny yellow with brown specks; I. reticulata comes in shades of blue, purple, lavender, maroon, white, and yellow. It has bright yellow and/or white markings on the petals. This species has a number of named cultivars, including ‘Harmony’ (deep cornflower blue) and ‘J.S. Dijt’ (very deep purple). All the photos on this page are I. reticulata. (Hybrid irises typically sold as “Dutch Iris” are larger, and bloom later in the summer.)
Both species have a three-part arrangement of petals and sepals, borne on a short stem rising from the ground, and narrow, green leaves with parallel veins. They have a delightful scent reminiscent of violets. Note that I. danfordia bulbs are poisonous.
These irises are grown from bulbs planted in fall. Pick a spot in full sun, and bury the bulbs about three inches deep, making sure the point is up and the roots are down. It’s a good idea to cover the area with three inches of mulch to keep down weeds and protect the soil from freezing and thawing during the winter. The bulbs are hardy to USDA Zone 5; if you’re concerned about colder temperatures, add even more mulch, but rake it off in early March so the soil can warm.
Dwarf irises require excellent drainage; bulbs sitting in constantly wet soil will rot. Digging three inches of compost into the soil at planting time can help drain heavy clays. If possible, allow the planting to dry out somewhat over the summer. If you’re planning on a single season of bloom, no fertilizer is needed. However, if you are hoping for some flowers in future years, apply nitrogen (and phosphorus, if needed) immediately after bloom. Be sure to let the fading foliage remain until it’s completely brown.
The plants are fairly short, reaching only three to six inches in height, with large flowers that dominate the small clumps of foliage. Because of their diminutive size, consider scattering them under deciduous trees, grouping them in the front of borders, and adding them to rock gardens. One way to achieve a natural spacing is to gently toss the bulbs into the area where you want them, then plant them where they fall.
The catalogs paint a glowing picture of expanding clumps and years of flowers. That happens in some parts of the country, but not necessarily here in Colorado. It’s true that if the bulbs’ needs are met, they’ll divide after blooming. However, these newly divided bulbs probably won’t rebloom the following year. They’re simply not big enough. It takes several years for these small bulbs to grow to blooming size. Happily, these bulbs are relatively cheap. Just assume you’re planting annuals. Who knows—you may be pleasantly surprised.