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
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
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
Are irises bulbs or
Actually, iris come in both bulbs and rhizomes - and there is a
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
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.
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.
The "Tall Bearded" (TB) are most common bearded, with an average
height of around 36".
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".
have different heights and blooming times, many bloom earlier than
"Miniature Dwarf Bearded" (MDB) - these are the smallest of the
bearded irises, growing up
to 8" in height. They require a significant cold
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
They are perfect for small areas.
"Miniature Tall Bearded" (MTB) -
usually blooming with the TBs, these 16" to 27
irises are dainty, and usually fragrant.
blooming between the SDBs and the TBs, these 16" to
27 1/2" perky irises have intermediate sized flowers,
clump well, making them idea for the smaller garden.
- also in the 16" to 27 1/2" range, these irises bloom
and closely resemble their TB cousins, but are reduced
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.
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
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
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.
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):
Senorita Frog (SDB)
Earl of Essex
Happy New Year
I Bless (IB)
Planting and Growing Bearded
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
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
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
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
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
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
- 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
- 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
For other growing information, go to AIS
Growing Information or visit one of our activities.
Planting and Growing Louisiana
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