Beautiful bearded iris, also referred
to as German iris, have some of the most colorful flowers in the garden. The iris family contains many species, the bearded
Iris we grow in our gardens are hybrids of some of those species. Bearded iris are hardy and easy to grow and
good for beginning gardeners. For a
splash of color in late spring and early summer, plant some bearded iris in
your garden.
Bearded irises are usually
grown as part of mixed borders. Small
varieties can be grown in rock gardens or even in pots and containers. They come in every color of the rainbow and
in many different heights, from 6” to 3’ or more high. In catalogs they are generally grouped by
height, flower size and bloom time. They
are a collector’s delight with hundreds of varieties on the market. The iris names are often as colorful as
they are.
Bearded irises have thick,
“sword- like” leaves and the plants form clumps. The bearded iris flower has six petals. Three petals stand upright and these are called
the “standards.” The other three petals
droop downward and are called the “falls.”
Each “fall” has a group of hair-like growths near its base called the
“beard.” Each bearded iris variety can
be all one color- beard, falls and standards, or each part can be a different
color. The flowers appear at the end of
long stalks in clusters. Some varieties
are fragrant. Bearded iris begins
blooming in mid spring with the dwarf and intermediate varieties, and continues
into early summer with the border and tall varieties. Some new varieties may re-bloom in fall when
the season is long and mild.
Growing bearded iris
Bearded irises are hardy in
zones 4-7. The best time to plant bearded
iris is late summer or early fall. They may
be sold in pots or more commonly, as bare rhizomes. A rhizome is a long, fleshy looking thing
with roots coming out of the bottom. It
will generally have a few leaves, called a fan, that have been cut to 3-4
inches. Don’t worry if the fan is dry
and yellow, as long as the rhizome is firm and plump. Mushy, soft, or shriveled, dry rhizomes or
those with holes in them should not be bought.
Long, branching iris rhizomes with two or more fans will give you bigger
plants and are more likely to bloom the first year. About 60-70% of bearded iris bloom the first
year after they are planted.
Bearded iris need full
sun. They need well drained soil, and
do well with little water after they are established. As growth starts in early spring, iris
benefits from a small amount of low nitrogen fertilizer. For the best chance of getting re-blooming
varieties to actually re-bloom, fertilize them again after the first bloom has
finished, and give them a little water if the summer is dry.
To plant iris rhizomes dig a
trench a few inches deep and make a little mound of soil in it. Place the rhizome on the center of the mound
and fan any roots out along the sides of the mound. Then re-fill the trench. The top of the rhizome should be just barely
covered in soil. In heavy clay soil the
top of the rhizome can even be left exposed.
Bearded irises will not bloom if they are planted too deeply. Plant the rhizomes 18-24” apart. The first year after planting the rhizomes
should be mulched with straw, oak leaves or other material that doesn’t mat
down. This is to prevent them from being
heaved out of the ground before the roots are established. Remove the mulch as soon as the weather
begins to warm. Bearded iris should be
kept weed free and they are one plant that should not be mulched during the
growing season. The tops of the rhizomes
need air and sun for the plants to do well.
To keep your bearded iris
plants looking their best remove each flower as it dies. When all the flowers on a stalk are finished
blooming cut the stalk down as close to the base of the plant as possible. Remove any leaves that yellow or have spots
and streaks on them, and cut all the leaves off close to the ground after frost
in the fall. This helps keep disease and
pests from over-wintering.
Bearded irises need to be
divided every 3-4 years for best bloom.
Over time the center of the clump stops blooming and if the plants are
too crowded, all may stop blooming. Dig
up the clumps after they have bloomed, wash off the rhizomes and cut apart the
clumps. Leave a nice section of firm
rhizome with a “fan” or two. Cut the
leaves on the fan back to a couple of inches.
Discard the old, woody and dry looking pieces of rhizomes from the
center of the clump and also discard any soft, black mushy pieces or rhizomes
with holes bored in them. Then re-plant
your divided rhizomes and share the excess with other gardeners.
In some areas bearded iris
may get iris borer. A night feeding moth
lays eggs on the plants near the leaf base.
These hatch into caterpillars which first feed on the leaves, then move
into the rhizomes. They are big, fat
pink things that eat the inside of the rhizome.
This leaves the rhizomes more susceptible to bacterial rot, which turns
the rhizomes black and mushy. To keep iris
plants healthy remove damaged and diseased rhizomes, cut back and remove leaves
before winter, and don’t over water.
The rhizomes of iris are
dried and powdered to form orris root and dried rhizomes are also used to make
perfumes.
Dividing bearded iris
August and
September are good months to divide your bearded iris. As irises grow they make huge clumps of
plants and as they get crowded your blooms will get less. Many, old crowded iris beds have only a few
blooms each spring, generally on the edge of the clump. Iris should be divided every 3-5 years to
improve blooming and keep the garden bed from being overtaken. You may also
want to divide iris to give some to friends or make another garden bed. If you need to move iris to another location
in the garden August and September are also good times to do it.
Irises make
new plants on rhizomes. Many people
think these are roots, but the roots actually grow from the underside of the
rhizome. Rhizomes are actually
underground stems and you will see joints or nodes along the rhizome with
leaves (or “fans” in iris jargon), popping up along each node. Rhizomes are
tan, knotty looking and can branch off in unusual ways. There should be roots on the bottom of
younger rhizomes. Each rhizome section
with its “fan” can become a separate iris plant.
It’s pretty
easy to divide iris and any gardener should feel competent to do it. You’ll need a good sharp knife to help divide
rhizomes, some scissors to cut the iris leaves and something to put your
divided rhizomes in. You may also want
some common household bleach for disinfecting rhizomes.
Decisions about divisions
Start by
deciding what you will do with the divided plants. If you need to prepare a new site you should
get that done. Irises will “hold”
outside of the soil for a few weeks but it’s best to get them planted as
quickly as possible. Contact your
gardening friends to see if they want some divisions if you think you’ll have
too many.
New iris
divisions will have flowers exactly like the plant you divided. If you want different colors or varieties of
iris you may be able to trade your divisions for them. Place an ad or contact local garden clubs if
you don’t have gardening friends to trade with.
If you need
to hold the divided rhizomes for a few weeks wash the soil off them, let them
dry in a sunny place for a few hours then put the rhizomes in a cool dry
place. You don’t want new growth to
start until you have them replanted so don’t store them in plastic bags or
anything that retains moisture.
Here’s how to do it
Dig the
whole clump of iris up. Irises have
shallow roots and this is easy to do. Make a circle around them with a spade and
then lift them up. If the clumps are
packed together in a bed you may cut through some with your spade as you lift
them but you will generally have plenty of good rhizomes left.
Put the
clump of iris on a tarp, a board, or on cement and gently wash all the soil off
the rhizomes with a garden hose so you can see what you have. Cut the iris leaves back to about 3-4 inches;
it doesn’t matter if they are cut on a slant or straight across.
After a
rhizome section blooms it will never bloom again. Examine the clump you lifted carefully. To determine which rhizomes sections are old
you can look for the flower stem. Old
rhizomes may also be devoid of roots and have tiny holes on the underside where
the roots fell off. In a clump old
rhizomes are generally in the center.
You’ll want
to divide irises between joints, leaving each section with one or two sets of
leaves and a healthy section of rhizome consisting of 2 or more joints. You can start new plants from a single node
or section, but they will be smaller and may not bloom for 2 years. Sometimes you can snap the joints apart with
your fingers but cutting is more precise.
If the old
iris rhizomes have new sections of rhizomes with no leaves or very small leaves
on them you can save the old rhizome and replant it with the young daughter
plants. It will provide food for them
until they grow more leaves. Otherwise
discard old rhizomes that have bloomed.
Examine the
rhizomes you are keeping looking for mushy areas or large holes in the top side
of the rhizome. Large holes may indicate
iris borers and there may be a large pink worm inside the hole. Those pieces should be discarded in the
trash, not the compost pile. In the
compost pile the pink “worm” can mature into the adult iris borer moth and
infect your other plants. Soft, mushy areas indicate bacterial rot and should
also be discarded.
Next add one
cup of common household bleach, without scent added, to a gallon of water and
soak the good rhizomes for 10 minutes.
Remove, rinse with clean water and and allow them to dry in a sunny
place for a few hours. This removes
disease organisms. You can re-use the
bleach solution for several batches on the same day. If you know the name or
color of the iris you are dividing you can write that on the leaves of the
divided pieces with a marker or add a label held on with a rubber band to the
piece.
Replanting
Replant the
divided sections of rhizome shallowly, root side down, leaves up, with the
surface of the rhizome just under the soil.
Plant the rhizomes 1 foot apart.
Iris bloom best in full sun positions.
If the weather is dry water the replanted rhizomes once a week.
If you buy
irises to plant or hold your divided rhizomes try to get them into the ground
by mid-September in zones 5 and lower, the end of September for zones 6 and
higher. This will make it more likely
that they will grow well for you and bloom the first spring. Larger rhizome sections will probably bloom in
the spring. Smaller sections may take
two years to bloom. Fertilizing with a
slow release granular fertilizer in early spring helps make strong plants and
large blooms.
If you take good care of your irises and divide
them faithfully you’ll have them around for years
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