About Iris

Growing Iris in our area

In our area, we have seen many old iris blooming in March and April.  Many of these that grow like "weeds" are old varieties, and don't need any care.  

The modern hybrid varieties are very fancy, and need more care.    We who grow many varieties have great fun and a longer blooming season, with early, mid and late blooming iris giving us beautiful blossoms from about mid March through early May.  A few varieties rebloom, in late May or during the fall season. 

In general, irises are hardy and can be transplanted anytime.  The best time for planting is in late summer when they are semi-dormant.  This gives them time to establish through the fall and winter, with higher probability for blooming the following spring.

Below is some general information about iris varieties classification and iris planting and growing.

For more local information, please visit some of our events and ask questions.

Are irises bulbs or rhizomes?

Actually, iris come in both bulbs and rhizomes - and there is a difference.

Dutch iris, iris reticulata and iris danfordia (there are others) are bulbs. Bulbs are modified BUDS surrounded by thick fleshy layers,  like an onion. They are normally globular in form. They often have either a smooth papery outer layer or one that looks more fiberous. Roots emerge from the bottom (basal plate) when the bulb is actively growing. Offsets are produced off this basal plate. Bulbs tend to "stay put" where you plant them, spreading very slowly over many years.

Bearded iris (Germanica), Louisiana iris, Siberian iris, iris tectorum, iris cristata, spuria iris and aril iris (there are others) are rhizomes. Rhizomes are thickened STEMS that grow horizontally just below the
soil surface. Rhizomes are normally elongated. They are solid, and may be smooth (Germanica, aril) or appear to have segments ringed with fiberous 'hairs' (Louisiana, spuria, Siberian). Roots are produced along the length of the lower surface. Offsets are normally produced at the growing points on the heel of the rhizome, but can occur anywhere along the rhizome. Rhizomes creep along under the surface and can spread rapidly, depending on the type of iris and the cultivar.

Both bulbs and rhizomes (along with croms and tubers) provide the plant with the same service of storing nutrients for growth, only they do it a bit differently.

Iris Classifications

There are a wide variety of iris classifications.  The general categories are bearded and beardless.  
The classification list below is brief.  For more information, you may go to some national iris web sites, or visit our local ISD events and ask questions.

Bearded iris:

The "Tall Bearded" (TB) are most common bearded, with an average height of around 36". 

Different varieties have different heights and different blooming times in our spring season. 

The "Median" types have several classification categories, and heights are less than 28". 

Various types have different heights and blooming times, many bloom earlier than TB's:

• "Miniature Dwarf Bearded" (MDB) - these are the smallest of the bearded irises, growing up to 8" in height. They require a significant cold period to prosper, and do not do well in the Dallas area.
• "Standard Dwarf Bearded" (SDB) - these are early bloomers that range from 8" to 16" in height. They are perfect for small areas.
• "Miniature Tall Bearded"  (MTB)b- usually blooming with the TBs, these 16" to 27 1//2" irises are dainty, and usually fragrant.
• "Intermediate Bearded" (IB) - blooming between the SDBs and the TBs, these 16" to 27 1/2" perky irises have intermediate sized flowers, and clump well, making them idea for the smaller garden.
• "Border Bearded" (BB) - also in the 16" to 27 1/2" range, these irises bloom with and closely resemble their TB cousins, but are reduced in size to  balance their shorter height.

The "Arilbred" types are a hybrid between the common bearded irises described above and the more exotic regelia and oncocyclus aril irises of the middle east and southern Asia. The less aril content, the more similar they are to growing TBs.   Most will grow in the Dallas area.

Bearded iris need some cool winter time to be happy for spring growing and blooming. 

Beardless iris:

The "Louisiana" (LA) are most common beardless, with height ranges similar to tall bearded.  Varieties bloom over the range of mid April through mid May in our area.  These need more moisture (see "Planting" below), and less need for cool winter.

The "Spuria" (SPU) type have some growing similarities to bearded iris, blooming with the late TBs and the LAs.  They resemble Dutch iris on steroids, growing to heights of over 40" and producing pampas grass like clumps.

Others:  "species", "Siberian", "Japanese", and a few others. 

Bulbous iris:

The "Bulbous" iris (e.g. "Dutch Iris") have a bulb-type base rather than rhizomes and bloom very early. Like most bulbs, they die back in the summer and come back in the fall/spring.

Reblooming iris: 

There are some bearded iris varieties that rebloom late spring and/or during the fall.  Not everything that is labeled a rebloomer will rebloom in Texas. Check with your local growers for varieties that rebloom here.
    Some reliable Dallas area rebloomers (all TBs unless otherwise noted):

Planting and Growing Bearded Iris 

After receiving bearded iris, it is better to plant as soon as possible.  If not, store them is a cool dry area until planting time is available.  They can survive easily being dry and cool. 

When to Plant:  Best time is August through late September.

Where to Plant:  Bearded iris need at least 4 hours of sun, and more is better.  Some afternoon shade is okay in a hot climate.  They need well drained soil, such as raised beds, and neutral pH soil.

Soil Preparation:  Iris will thrive in garden soils. Heavy clay soil must be improved by adding course sandy material (e.g. play sand, washed sand, etc.) and compost.  Some sulfur powder will help neutralize alkaline.  Prepare the soil by tilling or turning over the soil with a garden fork to a depth of at least 10 inches.  Also some fertilizer may be added in tilling of the soil.

Depth to Plant:  Plant iris so the tops of the rhizomes are at the surface, or barely covered, and the roots spread out and down on each side of a slight planting mound.

Distance Apart:  Iris are generally planted 12 to 24 inches apart.  They may be planted closer for immediate effect, but will need to be thinned out every other year.

Watering:  Newly planted iris need some moisture to begin to establish their root system.  But it should never be soggy, since it will increase possible iris rot.  Let the soil dry before next watering.  Periodic deep watering is more beneficial than frequent sprinkling.  Rebloomers will like to have a little more watering to prepare for their rebloom.

Fertilizing:  For iris in our area, we suggest a light feeding in mid October and mid February.  Bearded iris don't like excess nitrogen fertilizer, since it will promote rot.  Some suggested fertilizers are 10-20-10, or 13-13-13, or balanced organic fertilizer.  Some other fertilizer recipes are also suggested by experts.  The fertilizer is applied as a light top dressing, and possibly stirred a little into the top soil.  Iris will respond well to a minimum of attention, while they may not thrive with no attention.

Thinning:  Generally, iris need to be thinned and divided about every 3 to 4 years.  Crowded clumps may slow down blooming.

General Care:  We suggest to clean weeds and debris.  Iris don't care for mulch on the top soil.  Stalks can be cut close to the ground after bloom.  Do not cut back healthy leaves, but diseased or brown ones should be removed.  Keep diseased foliage out of the compost pile.

Iris Problems: 

1. Bacterial soft rot: this is mushy and smelly disease at the base of the plant, or sometimes on the bloom stalk.  Cut out and clean out the soft parts, and spray with a 10% bleach solution and maybe a powder, such as Ajax, on the infected area.  Also adding some sulfur powder may suppress bacteria. 
2. Fungal leaf spot: this starts as small brown spots on the new spring leaves.  It occurs generally in the spring when there may be some fungus in the ground and the air gets warmer and humid.  For this problem, spray with Daconil a few times to stop fungus growing.  Later in the season as the humidity goes down, the fungus stops growing.  To prevent this problem, spray with Daconil a few times early in the spring, or use a little bit of sprinkling fungicide with the fertilizer in February.  

For other growing information, go to AIS Growing Information or visit one of our activities.

Planting and Growing Louisiana Iris 

Louisiana Iris need at least 4 hours of sun.  These grow well in wet soil, such as a pond, so they don't need well drained soil.  That's why they were once called "swamp iris".  They prefer slightly acid soil, and they can accept more fertilizer than bearded iris.  But they actually tolerate a range of soil types, so they may be planted with some other flowers, such as daisies, daylilies, etc., as long as they can get regular watering, about an inch a week. 

For more growing information, go to: SLI Culture of Louisiana Irises