FREQUENTLY ASKED QUESTIONS
LACK OF BLOOM
IRISES HAVEN'T BLOOMED, WHY?
1 - Summer Sun. Irises require full sun for at least
half a day in summer. Insufficient summer sun does not allow proper development
of flowering. Full sun all day is desirable for most, however dark colored
blooms that flower later in the season will last better if given some protection
from the hot afternoon sun. Full winter shade is not a problem.
Even if your irises are in full sun, the rhizomes may be shaded
by mulch or creeping perennials such as violets or evening primrose. Ensure that
the soil over the rhizomes is not shaded.
2 - Winter Chill. Just as they like good summer heat, so
they like to be chilled in winter. The degree of chilling required depends on
the cultivar, but many Dwarf Bearded require actual frosts to bloom. Reblooming
irises may need less chilling than other varieties. Some people report good
success in inducing dwarf iris to bloom by putting ice on top of the plants a
number of times over winter. If you live near the waterfront in Adelaide it may
not be cold enough, similarly the western suburbs of Perth and eastern suburbs
of Sydney. Most of Brisbane would not receive enough winter chill.
Also be aware that if they are against a north facing wall, the
wall may retain enough heat at night to prevent sufficient chilling.
3 - Too Much Nitrogen. Excessive use of nitrogen rich
fertilizer can cause lush plants with little or no flowers. Bearded irises like
good supplies of phosphorous and potassium, and less nitrogen. We recommend
pelletised organic fertilizers such as Rapid Raise or Dynamic Lifter.
Alternatively use slow release such Osmocote.
4 - Needs Dividing. Irises can exhaust the soil after a
number of years, or grow too dense. Depending on the cultivar they will dividing
every 2-5 years. They should be moved to another spot or else have their soil
5 - Settling In. Sometimes when you buy a plant it may
not flower the following spring, but rather will concentrate on establishing
itself and then will flower the second spring.
6 - Mild Rot. The part of the rhizome most susceptible to
rot is the top of the rhizome where the flowering fan is. Sometimes this may
rot a little over winter and the rest of the rhizome survives and the newer
small fans along the sides continue to grow, but the fan that would have
produced bloom has died. This usually causes reduced bloom rather than total
lack of bloom.
1 - Recently Moved. Spuria irises don't like being moved
and usually will not bloom the following year. Occasionally it will take 2 years
to get bloom.
2- Lack of Summer Sun. Spurias like full summer sun.
SIBERIAN IRIS and JAPANESE IRIS
1 - Winter Chill and Summer Sun required. requirements
are as for tall bearded irises, except Siberian
prefer actual frosts.
SHOULD I DIVIDE MY IRISES?
The best time for Bearded Iris and Louisiana Iris is generally
immediately after flowering or in late autumn - early winter. If it is too close
to flowering time, bloom will be small, late or not happen at all. Moving
during summer is OK, but bearded iris don't grow much over summer so don't water
them a lot to get them to grow, you will only induce rot.
Irises that go dormant (Siberian, Spuria and Japanese and bulbs)
are best moved during dormancy. Spuria iris can be moved soon after they begin
their spring growth, but should be planted immediately and not allowed to dry
Pacific Coast Iris are fussy about when they should be
moved. They should only be moved once they have started their winter growth,
usually 4-6 weeks after the beginning of the autumn rains i.e. mid May - mid
Most species (iris I Ungicularis etc) should be moved in autumn
with the rains.
HOW DEEP SHOULD I PLANT MY IRISES?
Bearded iris should be fairly shallowly planted, with about 1-2
cm (half inch) of soil over the rhizome. Too deep and they won't get enough
summer heat or winter chill. If exposed to the sun they may develop scorch in
the Australian climate. (Books that talk about exposing the rhizome are generally
written for cooler climates where every effort is required for sufficient summer
When replanting ensure that the bottom of the rhizome makes good
contact with the soil underneath it.
Other (beardless) iris should be planted a bit more deeply,
2-4cm. If your Louisiana iris rhizomes end up above the surface of the soil, it
doesn't really matter.
TRIM MY IRISES ?
Irises need only to be trimmed when moved. The leaves are cut
back because the roots have been cut. There is no need to trim any other time,
simply remove old, spent leaves.
IRISES ROTTED, WHAT HAPPENED?
Bearded Iris are more easily killed by over-caring than
anything else. Excessive moisture, especially over summer will induce rot. Make
sure your bearded iris are well drained. Do not cover the rhizomes with moisture
holding mulch (e.g. lawn clippings, pea straw), particularly if you use overhead
watering. If rot starts to happen, remove the rotten part of the rhizome and
expose the cut surface to the sun for a few days, then replant. Excessive use of
nitrogen fertilizer can produce lush plants susceptible to rot.
Spuria iris don't like summer humidity, so don't cover
with damp mulch in summer. Some parts of Australia e.g. Coastal Sydney and
north where there is very high summer humidity may not be suitable at all.
MUCH SHOULD I WATER MY IRIS?
Bearded Iris - once every week or two over summer will be
fine. Once a clump is established, many will survive without any summer
watering. In a dry spring some watering to keep the soil slightly damp may be
required. You may put mulch over the roots, but not over the rhizome. When
transplanting in summer, water once or twice a week for the first few weeks then
no more than once a week. If your irises go completely dormant from lack of
water over summer, don't worry they will start growing again in autumn, as long
as the rhizome is still fairly firm. In pots water them 2-3 times a week in very
Spuria Iris - Should not be completely dried out until
flowering has finished. Once flowering has finished, if not watered they will
die down, go dormant and then come away again with the winter rains. If watered
every week or two through summer they will remain green until about April when
they will briefly die down , then start their winter growth.
Louisiana Iris are swamp irises so need plenty of
moisture during winter-spring. They can be mulched fairly heavily. If growing
in pots immerse the pots about 2/3 in water but not completely. They can survive
reasonable summer dryness but are best kept moist all year round. If they do dry
out rehydrate slowly rather than suddenly soaking in water.
Siberian Iris are bog irises and like good winter and
summer moisture. Once they go dormant in late summer, they can dry off somewhat.
It's OK to mulch them heavily.
Pacific Coast Iris like good moisture in winter and
spring but not boggy. In summer occasional watering is best, but some seem to be
happy with complete summer neglect.
Japanese Iris like relative dryness during winter when
dormant and plenty of moisture during the growing period over spring and summer.
If growing in pots in a pond remove from the pond during winter.
MY FLOWERS ARE DEFORMED, WHAT
Frost Damage - Frost on blooms are out will cause the
flowers to go a bit transparent and mushy. Buds that are fully formed will also
be damaged by heavy frost. The edges will be slightly curled, ruffling will be
lost and plicata colouring will speckled. Damage may persist for several weeks
after the frost. Some cultivars will be damaged more than others and it will
worse in the more exposed, lower parts of the garden.
Weed killer Damage - Glyphosate type sprays (eg Roundup)
used within a couple of months of flowering will damage the blooms. If slight
traces have drifted onto the plant the blooms will be whitish around the edges
and some ruffling lost. Heavier exposure will lead to completely deformed
blooms. Slight exposure to glyphosate will not normally kill your irises but
newly transplanted ones will be more susceptible.
Mild Glyphosate Damage More Severe Glyphosate
Damage - Dutch Iris
Very Severe Glyphosate Damage - Tall Bearded Iris
MY BEARDED IRISES HAVE TURNED WHITE
There are no proven cases of irises actually turning white,
however there are several reasons why your patch may end up being all white.
Firstly - glyphosate damage -see above. Secondly the patch has been taken over
by a white one. Some white cultivars are extremely vigorous and will overgrow
less vigorous cultivars. There may have just been a small piece left from
previously or else occasionally nurseries make mistakes and a piece of white was
mixed in with what you bought. It didn't flower for several years but multiplied
rapidly. Then, by the time it bloomed, it had taken over most/all of the patch of
THE FLOWER STEMS
WITHER IN THE MIDDLE AND FALL OVER.
This usually happens as a result of weather damage. If the
withering is mid- stem it is caused by wind and sudden weather change drying
out the stem during a period of very fast growth. Some cultivars will be more
susceptible than others.
If the stems falls over at a junction in the stem and is
brownish and mushy, water has been trapped in the little leaf at the junction
and rot has followed. Usually happens in very wet springs, especially if warm
If there is steady wind while the flower stems are growing
quickly they will tend to grow almost sideways and the straighten once the wind
Louisiana stems are naturally a bit snake-like.
Very mild silver speckling is caused by hail. Not a
problem in itself but it does seem to make the plant more susceptible to fungal
Hail - left Fungal Leaf Spot - right
Fungal Leaf Spot
Fungal leaf spot is brownish circles over the leaves.
Some people just ignore it, if severe you can spray with fungicide. Because most
irises have waxy leaves a systemic fungicide may be best as complete coverage
would not be required, however they are toxic. See your garden centre for advice.
Brown Tips happen over summer. Usually caused by dryness
and/or salt accumulation from salty water (e.g. bore) You can trim it off if it
Snail damage is sometimes caused by tiny white snails,
producing torn looking leaves. Some cultivars seem to have less waxy coating and
are more susceptible.
Pineappling - is when the leaves grow short, tight and
sort of scrunched. It is caused by climate change, often worse on new stock or
when the weather is very changeable. Will come right in time.
WHAT SHOULD I FERTILIZE WITH,
We recommend generally fertilizing with Rapid Raiser, Dynamic
Lifter or Osmocote. However irises that like very acid soil (Louisiana, PCs and
Japanese) are best fertilized with aged cow manure (the most acid animal manure)
or azalea and camellia fertilizer.
It is best to fertilize when transplanting and then at the
beginning of the growth period, a couple of months before flowering.
WHAT SORT OF SOIL AND
CLIMATE DO IRISES LIKE?
Bearded Iris and Spuria - neutral to alkaline soil is
best, needs to be well drained. If extremely acid may benefit from a little lime.
Best suited to climates with relatively dry summers and cool to cold winters.
Louisiana - need damp - wet acid soil. If your soil is
neutral or alkaline then plant in very large pots with a mix of old cow manure
and acidic potting mix. Immerse pots two thirds in water. So long as adequate
summer moisture is provided, climate is not a problem. One of the few irises to
do well in tropical areas.
Siberian Iris - need damp- boggy soil, preferably fairly
neutral. They need frosty winters to flower properly.
Pacific Coast Iris - need acid soil. Better in areas with
relatively dry summers and cool damp winters. Do well in largish pots of acidic
Japanese Iris - need acid soil. Should not to be immersed
in water through winter and need good summer moisture. Need some winter cooling.
HOW LONG CAN MY IRISES STAY OUT OF THE GROUND?
Bearded irises can survive out of the ground for several
months, if stored in a cool spot. Soak for an a couple of hours before planting.
Others are best replanted as soon as possible, although they
will survive a while if kept cool and damp. Louisiana irises can be stored in
shallow water for a few weeks.
Article - courtesy of Impressive Irises