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There are many species of
Iris
and most of them originated in the
Northern
temperate regions. They are
monocotyledons and some
of them spread by
rhizome
while others come from
bulbs.
Like other monocots, their flower parts are usually
in groups of 3. They have 3 upright petals called
standards and 3 horizontal or recurved petals called
falls.
Illustration of flower parts.
In milder climates, there are
enough different species of Iris to keep them in
bloom practically all year round. Each plant may
only flower for 1 to 3 weeks but the sequence of
blooming species can keep the flowers coming.
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Since this is a fairly large genus of plants, the
required site conditions can vary greatly among
different types.
- Typical Site - Most of the types of
Iris
need a well drained soil to avoid root rots.
This includes the
tall bearded iris.
- Wet Site - Some iris such as the
Siberian
and
yellow flag iris can actually grow in a pond
or bog garden.
Check on the
species of iris you wish to grow.
Other site conditions would include full sun.
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The best way to learn how to
plant something is to look at growing on other
locations. Iris that grow from
rhizomes
always grow
with the rhizomes just at the surface of the soil.
Therefore, avoid the most common mistake which is to
bury the
rhizome as if it were a root. Plant these
types of iris so that the rhizome is just beneath
or at the soil surface.
For the bulb type iris, follow
the old rule of thumb for all bulbs. The depth of
the planting hole should be 2 to 3 times the height
of the bulb. Most bulbous iris are rather small so
they don't need to go very deep into the soil.
Plant the bulbs in the fall and
the rhizomateous ones may be planted in either
spring or fall. If planted in the spring, you won't
generally get any flowers that summer. Also
regardless of the season, sometimes iris will not
bloom the first year after being planted.
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In the early spring before growth
begins, clear the beds and borders of any debris
from the previous growing season. It is especially
important to remove an old foliage from iris that
were infected by leaf spot diseases the previous
year.
Once the growing season begins,
you can side dress the iris with the same fertilizer
that you use for other perennials. It is always good
to have your soil tested every 3 or 4 years to be
sure the pH and nutrient levels are adequate for
plant growth.
When the blooms fade, cut off the
spent flowers (deadhead) since there is no sense
letting the iris use its energy to produce unwanted
seeds.
Take care while weeding around
the iris so that the rhizomes don't get damaged.
This could open them up to root rots and encourage
iris borers to attack.
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Bacterial Soft Rot - This is
by far the most damaging problem of iris. It is
caused by a bacteria in the Erwinia genus
similar to the one that causes
fireblight on
pears,
apples and other trees.
For the bacteria to enter the plant, it needs
some sort of opening in the top layer of the
rhizome. This could happen during weeding,
winter injury, by stepping on the rhizome or by
iris borer feeding. Once it is infected, the
rhizome will turn to mush and have a peculiar
odor.
This type of rot is more prevalent in irises
that are under stress. This may be from being
planted too deep, poor drainage in the soil, too
much fertilizer or when clumps become crowded.
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Iris Borer - The larvae of a
certain moth emerges from the egg in the spring
and crawls to the top of the iris foliage. They
bore an opening and begin to feed as they move
downward between the layers of the leaf.
Eventually, they reach the rhizome where they
finish feeding and bore out to pupate in the
soil nearby and turn into the moth which lays
her eggs in debris near the iris and it all
starts again.
First indications of an infestation are small,
ragged notches on the edge of the leaves and the
accumulation of sawdust looking frass
(droppings) at the base of the leaf. As they
work their way downward inside the leaves, the
foliage may turn yellow and then brown. When
they have finished feeding later in the summer,
the drill their way out of the rhizome leaving
pencil lead sized holes. The larvae then drop to
the ground, pupate in the soil and turn into the
moth.
So, be sure to clean up the dead foliage and
other debris from the iris patch in the fall if
borers have been a problem. Sometimes the borers
can be felt inside the leaf and may be killed by
squeezing. Certain
insecticides may also be used
to help control this pest.
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Leaf Spot Disease - This
fungal disease is more of an aesthetic concern
rather than a serious enemy of the plant. If
there are large numbers of spots, it may cause a
weakening of the plant due to loss of leaf
surface for
photosynthesis. Again, removing debris from the
previous year's foliage will help to minimize
this problem. Also, planting iris in full sun
will help to keep the foliage dry and, thus,
discourage fungal diseases from starting.
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If your plants are selected properly and are
rated for your specific
USDA Hardiness Zone, there should be no need for
extra winter care.
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When the clumps of iris get very
crowded with newer rhizomes, they may begin to
flower less and less each year. When this becomes a
problem, it is time to divide the plant and reset
the divisions so that they allow proper spacing between
plants.
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