Irises in Containers

by Tom Waters

Irises are not usually thought of as container plants, but they can grow quite well that way, and there are a number of advantages to doing so.

Two Iris pumila cultivars,
'Wild Whispers' (Coleman, 2012) and
'Royal Wonder' (Coleman, 2013),
growing happily in a large container

The irises I choose to grow in containers are mostly dwarf bearded irises and the smaller arils and arilbreds. Tall bearded irises look out of place in even the largest containers, and a light container soil mix may not give them the support they need when top-heavy with bloom. The smaller irises, however, are naturals for container culture. They bring the plants closer to eye level for viewing, and allow them to be moved from place to place for best effect. If attractive containers, like oak barrels or terracotta pots are used, the effect can be quite lovely and dramatic.

There are additional advantages to container culture. I tend to put rare or choice plants into containers when I first acquire them, as it makes them much easier to weed and care for. A small iris that might get lost in an overgrown summer garden and succumb to neglect, is kept safe in a container where it can get the attention it needs.

Two forms of the exotic oncocyclus species Iris paradoxa
in a large container with a gritty soil mix

Arils are another good candidate for container culture in climates where summers are too wet to grow them successfully in the ground. The container can be stored in a warm dry place through the irises' summer dormancy period. It is also possible to provide a coarse, well-draining soil mix that would be difficult to maintain in the open garden.

As a hybridizer working with dwarfs and other small irises, I also appreciate that containers make the blooms more accessible. It's much nicer to pull a chair up to a container than to crawl around on the ground to harvest pollen or make a cross.

Most of my containers are inexpensive plastic models, in the largest size possible (two to three feet in height and diameter). Even the smallest irises enjoy a wide and deep root run. I fill them with various soil mixes, depending on what I have at hand, but I usually use a mix of my garden soil (a somewhat sandy silt) and commercial potting soil, sometimes with addition of compost, coarse sand, or even small gravel. The irises do not seem too picky about the exact composition of the potting mix. I like to use a top dressing of gravel as a mulch. It also looks nice, especially if a few rocks are positioned on top to make a miniature landscape.

Even in a container with enriched soil, irises will not go forever without dividing them and refreshing the soil mix every few years. Keep an eye out for overcrowding or declining vigor. Also, it is important to keep to a regular watering schedule; how frequently you water will depend on your climate, but the only time I have lost an otherwise healthy plant in a container was when I accidentally let it get bone-dry in the summer. Containers are less forgiving in this way than garden soil.

If you've never grown irises in containers, give it a try this year! You may find it offers both esthetic and practical rewards.

Iris reichenbachii blooming profusely in a container