Bearded irises
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For me the highlight of mid to late
spring is the flowering of the bearded irises. Sure, their flowering period is
all too short; but the huge range of colour, and more importantly the colour
combinations, make for a marvellous show.
Although the notion that familiarity
breeds contempt can apply as much to plants as anything else, my appreciation
of bearded irises has only increased as I have become more familiar with them.
Other irises produce larger blooms, flower over a longer period or are less
exacting in their cultivation requirements, but few can match the flamboyance
of the bearded irises. Bearded irises en masse are a never-to-be-forgotten
sight.
They are superb plants for growing in
large drifts and the ease with which they multiply means that you can build up
stock quite quickly even if you start with only a few rhizomes. All you need is
a reasonably sunny area of light, well-drained soil. There is the drawback that
the iris garden will be bare for much of the year, but for that brief period in
spring you will be amply rewarded.
So what are bearded irises and how do
they differ from the other irises? The most obvious characteristics are the
strongly upright, sword-shaped foliage (rather like a shorter, broader Gladiolus
leaf) and the small tuft — the beard — on the lower petals or falls. Most other
irises have narrow, rather strappy leaves and their falls lack beards or have
very reduced beards, though they may bear fancy markings. Bearded irises grow
from rhizomes as do the crested irises and some other types, while other like
the Dutch irises grow from bulbs. There are also technical botanical
differences, though once you’ve seen bearded irises you’re unlikely to confuse
them with any other forms.
It’s worth noting at this point that most
botanists now recognise the work of the Russian botanist Rodionenko, who
divided the genus Iris into several smaller genera. Strictly speaking
the bulbous irises —Dutch and English, reticulatas and Junos — are no longer
classified as irises. Instead they are now in separate genera: Xiphium,
Iridodictyum and Juno. The bearded are sometimes called ‘true’
irises because they are considered the type form against which all others are
compared. They fall into the section Iris of the subgenus Iris of
the genus Iris, and you can’t get more iris than that!
Anyway, botanical points aside, it’s
going to be a long while before gardeners accept this reclassification.
Especially when you consider that Rodionenko first published his work in 1961.
Types of bearded iris
Bearded irises come in several distinct
forms; all have similar flowers but vary in plant size. Most growers follow the
guidelines laid out by the American Iris Society, which recognises six groups:
Miniature dwarf
Up to 21 cm high and the first to
flower.
Dwarf or standard dwarf
Up to 40 cm high, very
heavy-flowering and slightly later than the miniatures.
Intermediate
Up to 70 cm and a bit later than the
dwarf but earlier than the tall bearded irises.
Miniature tall
These are again up to 70 cm high.
They flower at the same time as the tall, and the slender-stemmed flowers are
carried well above the foliage.
Border
These flower at the same time as the tall
but only grow to 70 cm high. Like a tall bearded — strong stems and
flowers just above the foliage — but smaller in all proportions.
Tall
These are the last to flower, usually
around early to mid November in Christchurch, and may reach 1.2 m high.
They are sub-divided into groups based on coloration and pattern but
understanding the groups is really only for the dedicated iris grower.
There is also a seventh group known as
the Aril irises. These are tall plants with very large flowers that
occur in some unusual shades including some with almost metallic tones. The
arils are subdivided into onocyclus, regelia, pseudoregelia and psammiris
groups, and are somewhat fussy to grow as they need very little summer water.
The plants that result when arils are crossed with the true bearded irises are
called arilbred irises.
Colours
The range of colours in modern bearded
iris cultivars is incredible and increasing all the time. One flower can
exhibit many colours and much of the beauty of bearded irises comes from the
way the hues and tones are combined.
The American Iris Society produces an
annual list of their top 100 cultivars and while many of their plants are not
available here it does provide a guide to the trends in iris breeding. I could
list many beautiful cultivars but descriptions could not do the plants justice.
It’s probably better to let the photographs do the talking. Do bear in mind,
however, that as bearded irises have only a short blooming, hence selling,
season, garden centres do not stock a wide range. Most of the plants shown here
are only available through iris societies and specialist growers. Nevertheless
all bearded irises are beautiful, so if you can choose your plants when in
flower, there’s really no need to be to concerned about getting a particular
cultivar.
Cultivation
Beautiful flowers are all very well, but
they are no good if you can’t grow the plants. One of the most appealing things
about bearded irises is their ease of cultivation. Any reasonably sunny place
will do, provided the soil is well-drained. The soil doesn’t need to be very
deep as bearded irises are only shallow rooting, but good drainage is vital or
the rhizomes will rot.
A light, neutral to acid soil with a
reasonable level of humus is ideal. Peat or finely chopped compost can be used
to open up clay soils but don’t add coarse organic matter or poorly composted
material as it may harbour the fungal spores that can lead to rotting.
A light dressing of dolomite lime every
two years will provide calcium and prevent the soil becoming too acid, while a
general phosphate based fertiliser will supply the main nutrient requirements. Do
not use high-nitrogen fertilisers as they encourage soft growth that can lead
to foliage fungal disorders or rhizome rotting. The aim is to keep the plants
growing slowly but steadily.
Don’t plant too deeply, the top of the
rhizome should be just visible. Planting on slightly raised mounds will prevent
the tops of the rhizomes from getting wet and will aid the drainage.
Water the plants in spring if the weather
is dry, and allow them to dry off after flowering. Too much water, even excess
humidity, will encourage them to shoot in the autumn rather than the spring.
This can be fatal and has led some gardeners to regard bearded irises as fussy.
If you live in a damp, humid area, try planting close to the house where the
foliage is sheltered by the eaves, or under a tree, provided it doesn’t cast
too much shade. Aril irises thrive in a dry summer environment and appreciate a
good summer baking. They also prefer a slightly more alkaline soil, say an
annual dressing of half a handful of dolomite lime per plant.
Although bearded irises will often thrive
without any extra care, they are subject to attack from debilitating and
disfiguring fungal diseases. Under dry conditions these rarely present any
major problems, but in humid climates you may see rhizome rot, crown rot (where
the leaves join the rhizome) and the black patches caused by bacterial leaf
spot. Rust may also occur.
Good plant hygiene (removing damaged
leaves and tubers), avoiding overcrowding will go a long way to eliminating
disease. However, you may also need to spray with occasionally with a systemic
fungicide.
Insects and other pests do not cause many
problems but watch out for slugs and snails on the new shoots. Nematodes and
eelworms can damage the rhizomes, which may in turn lead to rotting. Aphids,
thrips, red spider and two spotted mites may also occasionally appear. Mild
insecticides like the fatty-acid sprays will control surface pests but you will
need to use a systemic insecticide to reach pests inside the rhizome.
Dividing bearded irises
Propagating bearded irises is simply a
matter of dividing the rhizomes, yet no aspect of iris culture is more
confusing to the beginner than knowing when and how to divide. This is not
because the process is in any way difficult, rather it is because pet theories
and strange ideas abound. The truth is there are no hard and fast rules, and as
always a lot depends on your climate and particular growing conditions.
Clumps of bearded irises should be
divided when their flower production shows signs of diminishing. This is
usually around every 3 or 4 years. It is a good idea to move them to a new bed
with freshly prepared soil in order to avoid a build-up of diseases or pests in
the old bed.
Although the rhizomes can be divided when
the last flowers have faded, most growers prefer to wait about 4 to 6 weeks
after blooming, say around late November for dwarf irises through to late
December for the tall bearded irises.
Dig up the clump (use a fork, gently
loosening and lifting to avoid damage) and hose off the soil. Once you have a
clean rhizome cluster, you should be able to see several points where strong
fans of leaves are growing. These are likely to be a the tip of the rhizome
where there will also be several fine feeding roots. Using a sharp knife, cut
the rhizome about 15–20 cm behind the leaf fan. The inside of the rhizome
should be white. You will now have a fan of leaves and a length of rhizome with
attached feeding roots. All that is required is to dust the cut with flowers of
sulphur or another fungicide, trim back the foliage to about half length, and
replant, taking care not to plant with the top of the rhizome at or just above
soil level.
Some growers prefer not to trim back
foliage, citing the fact that it does little to cut down water loss through
transpiration while reducing the leaves’ ability to photosynthesise. Although
this is true, there is a more important reason for trimming back the foliage:
to lessen wind resistance. Bearded iris are not held firmly in the ground by
their roots and fresh divisions may have difficulty if they are continually
moved around by the breeze. Even with foliage trimming, you may need to peg
down the rhizomes with wire hoops until established.
Provided you keep an eye out for any
fungal and pest problems and deal with them before they get out of control, the
rhizomes should re-establish well and produce strong flower spikes the
following spring.
Copyright Geoff Bryant
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