Great Plants for Michigan Gardens: Bearded Iris

Bearded irises are the stars of my perennial garden in May. Their tall, frilly blooms and strap-like foliage add a perfect upright element to the garden, and they come in such a huge variety of colors that you are unlikely to ever get bored growing them.

Where to Plant Bearded Irises

When planting bearded irises, you’ll either be started with dormant rhizomes or potted plants. Either way, you’ll want to plant your irises at least sixteen to eighteen inches apart to allow for plenty of air circulation. If you’re starting with a plant, simply plant it as deeply as it was growing in its container. If you are starting with a rhizome, you really want to make sure you don’t plant too deeply. Burying the rhizome will result in weak bloom or rot. The best way to plant the rhizome is to form a mound of soil in the planting hole. Set the rhizome on the mound, and arrange the roots around it. Then, backfill the hole, covering the roots, but leaving the rhizome exposed. I know — it looks wrong. Do it anyway. Your irises will thank you later with plenty of blooms!

Bearded irises really grow best in full sun. You’ll get the most numerous, larger blooms if they get at least eight hours of sun per day. However, if you have light or dappled shade, they’ll also grow and bloom well for you. Just as important as the amount of sun, however, is the quality of your soil. Bearded irises prefer fertile, well-drained soil. Lean soil will result in less-than-stupendous blooms, and soil that stays too wet will result in your rhizomes rotting over the winter.

Here in our garden, where clay is dominant (as it is in many Michigan gardens, at least if you’re away from the coasts) we’ve found it necessary to amend the soil before planting the rhizomes. Dig out an area, and mix a good amount of finished compost into the native soil. This will help lighten the soil overall for planting, and, if you side dress with compost regularly, over time the soil will improve a great deal. Obviously, you’ll want to avoid planting bearded irises in any low areas of your property — any place that water collects and sits will just spell rot for your rhizomes.

The best time to plant irises in Michigan is in June through September — this allows the plants to get established before winter.

 

How to Grow Bearded Iris

If you’ve planted your bearded irises in good soil in a sunny spot, there’s not much you need to do, day-to-day, to keep them happy. I side-dress my irises with fresh compost every spring, and deadhead them after they’ve finished blooming in May.

One of the most important things you can do for the health of your bearded irises is to make sure you remove all of the spent leaves and flower stalks after they’ve been killed back in fall. If you leave the foliage attached to the rhizomes, it provides the perfect place for iris borers (more about these vile jerks later) to overwinter.

You’ll also want to divide your bearded irises every three to four years to keep them growing strong. Once you start seeing decreased bloom, it’s time to divide. I’ll have more on how to do that in another post.

 

Bearded Iris Pests and Diseases

If bearded irises have a rep for being a little on the fussy side, it’s not their fault — blame the pests that like to plague them instead. The main one, which I alluded to above, is the iris borer. Here it is, in all its grossness:

 

Photo by: Bob Gutowski, Flickr Creative Commons Attribution License.

Iris borers can absolutely destroy your irises. They start on the leaves, boring their way in, down into the rhizomes, and then back out again. They cause a lot of damage, and the holes they make encourage rot as well. The best way to fight them is to not leave leaves and stems available for them to overwinter in. If you find borers in your rhizomes, you can try to cut them out with a knife, then replant the rhizomes as long as there is at least one “eye” left. You can also soak the rhizomes in a bucket of water — the water will drown the borer, and then you can remove any damaged sections of rhizome, and replant.

Aside from iris borers, bearded irises also contend with a few other pests, though these generally don’t cause as much damage as the borers:

  • Slugs
  • Snails
  • Aphids

 

Here in our garden, we have bearded irises planted with shasta daisies, oriental poppies, and alliums, and they bloom together and look wonderful. The shape of their leaves adds a nice, somewhat spiky touch to the garden, so even when they’re not in bloom, they have an impact. And because they come in so many colors and sizes, you can really have a lot of fun coming up with new combinations in your own garden.