Growing Irises

There are three main categories of irises. 

  • Bearded (Rhizomes, Native to Mediterranean Europe, Asia)
  • Non Bearded (Rhizomes, Native to North America, Europe, Asia)
  • Bulbous (True bulbs native to Mediterranean Asia and Africa)

Generally, most people think about and grow Tall Bearded irises. If planted shallowly, in well drained soil and full sun, they are quite trouble free only requiring weeding and the occasional application of pelletized lime to maintain soil pH.  When given dry, sunny spaces, they thrive on neglect.  But if rain and/or sprinklers keep them wet, and weeds retain the moisture, they can quickly succomb to bacterial soft rot. 

Conversely, non-bearded iris (Louisiana, Siberian, Japanese, Pseudacorous, and Virginica) are all considered to be swamp irises.  While they do not require submersion in water, they grow more robustly where water is plentiful.  These also prefer acidic soils, so liming is not necessary.  Additionally, some shade and supplemental water during dry periods is greatly appreciated.

Generally, Iris rhizomes are planted 12 to 24 inches apart.  The closer they are planted, the sooner they will desire dividing to prevent overcrowding, increase air circulation, and/or make space for new varieties. 

Bulbous iris (florist varieties), like conditions similar to bearded irises.

Regardless of type, irises dislike high nitrogen fertilizers.  We typically lightly apply a 6-12-12 fertilizer in March and also around June 1.