Weekly Express-News Article
By Calvin R. Finch, PhD, SAWS Water Resources Director, and Horticulturist
Saturday, November 3, 2007
“Iris, Great Choice for San Antonio”

Iris are desirable plants for San Antonio landscapes for a number of reasons.  They are very tough and qualify as xeriscape plants.  Pests are not a problem.  Even our largest garden pest, white-tailed deer, do not eat them in most situations.  The blooms are beautiful and the foliage is attractive.  Iris beds make a good groundcover in full sun with the swordlike foliage providing a different look and texture than most groundcovers.

There are many versions of iris, but the two selections that are best suited for area landscapes seem to be the cemetery iris and the bearded iris.  The cemetery iris are the plants that seem to survive and bloom on every old homestead and cemetery.  They have blue or white flowers that appear in February or even January some years.  They make the best groundcovers, because the blades are shorter and they provide a more dense cover.

Bearded iris are the big plants you see blooming in April with large orchid like blooms of white, yellow, blue, purple, maroon, salmon, brown and many bicolors.  Many have very pleasant fragrances.

November is the best time to thin iris beds so it is an ideal time to score the extra rhizomes that are removed from the gardens of friends and neighbors.  Retail nurseries also sell rhizomes now through the spring.  They can also be purchased as container plants.  The advantage to purchasing the container plants is that they will bloom the first spring.  They rhizome planted iris may also bloom the first spring, but it is less certain.

New beds should be located in full sun.  Iris respond to soil enriched with two inches of compost and a cup of slow release lawn fertilizer incorporated into every 50 square feet of the bed, but they are not fussy about soil.  Plant the rhizomes so that the top surface is level with the soil surface.  Iris rot if they are planted too deep.  Iris are also one of the few plants that do not seem to benefit by mulch.

Control Bermuda grass with one of the contact herbicides specific for grasses.  Fusilade, Vantage, Over the Top and Grass be Gone are some of the brands that work well.

If you have an established bed of iris, consider thinning it.  Iris are great plants for San Antonio landscapes, but for best performance they do need to be thinned out every 4 or 5 years.  Identify the best looking plants in the bed and mark them to stay in place.  Leave one of the smaller cemetery iris every foot and the larger bearded iris every 1.5 feet.  Dig up the rest.  It is not a difficult job because iris rhizomes are on the surface of the ground.  You do not have to be overly careful to retain the roots, because the rhizome will grow new roots.  Discard rhizomes that have been hollowed by insects or show any rot.  Large rhizomes can be broken apart at any joint to form new plants.  It is best not to break the rhizomes into pieces smaller than 3-4 inches if you want them to bloom within one growing season.  The blades (leaves) on the parent can be trimmed to 4 inches tall if you want to store them or find it easier to replant.

You can start new beds with the rhizomes thinned from the old bed or distribute them to friends.  The rhizomes store well in a brown paper sack in an air conditioned room or even a shed.  The individual rhizomes can even be planted in 1 gallon containers until you find them a new home.  Iris are popular plants at plant exchanges such as the Festival of Flowers in May.