- Thanks Billie
Gray for an informative overview of iris culture. Her first bit of advice was on choosing iris from a
catalog, "do not just depend on the photograph; read the
description, too". The advantage of buying your iris locally is
they are acclimatized. Many iris out of our area are better off to
age first before planting (let them sit and dry) until new roots
show and they become hardened off. Choose nice, fat firm rhizomes.
When choosing a location to plant, remember large iris rhizomes need
a lot of sun and good drainage. When planting, trim off old
shriveled leaves and trim roots with scissors. Make a mound, drape
roots over mound and pull soil up. Leave the top of the rhizome
barely exposed to the sun; do not plant deep. Spacing is best at
12"-24" apart. Try to get three of the same variety and plant them
in a triangle together.
Water well in the Spring and after planting, then let dry off for
about six weeks. In the summer, they do like to dry out between
watering, then in August and September resume plenty of water again.
It is best to water early in the day, so plants dry out during the
day. However, Japanese Iris do not like to dry out.
You should have continuous bloom each year, if you follow a division
program every 3-4 years. When you divide, discard the center with
the bloom stalk (mother rhizome) because it will not bloom again.
The two on each side are the ones that will provide the bloom next
When cleaning the iris in the Fall or Spring, old leaves can be
taken off by cutting or pulling. However, a word of caution.
Tearing an iris can release toxins. If you tear, wait until Spring
when leaves are dead. Do not injure the rhizome, as any cut or
injury will allow bacteria to enter and start to rot. Be careful
when you are weeding, too.
Low nitrogen fertilizers are best, including bone meal and
phosphorus. Feed iris early in the Spring and again after bloom. A
5-10-10 once a year is good, too. Something like Osmocote pellets
or another timed release fertilizer with a high middle number as a
top dressing. Iris respond well to Epsom Salts, about 2 tablespoons
around each plant in the Spring.
As far as insect attacks, we don't have a lot of problems in our
climates. Borers are rare, some aphids and some thrips but sprays
such as insecticidal soap will help control this. She didn't
mention deer, but I find an occasional chomp from them.
Rot and leaf spot are more bothersome for our area, mostly because
tall bearded (TB's} don't like wet feet or overhead sprinkling. If
you do find rot in a rhizome, take it out. You can destroy the
rotted rhizome and save the increases on the side; the white roots
at the back or heel are the productive ones. Cut the rot with a
clean knife, not serrated. Don't replant right away; instead let it
ripen or callus for a few days first. Do not leave it on the ground
where it will get watered. It's better not to replant in the same
space. If you do want to replant in the same space, remove some
soil and add fresh soil. Treat a fungus with two unbuffered aspirin
tablets per gallon of water.
Leaf spot is a series of blotchy spots on the leaves. This
infection is splashed on the plants from overhead watering, because
it harbors in the soil. If lesions are severe, you may need to cut
the plant all the way down. You can treat it with a copper sulphate,
Bordeax mix. Pea gravel around the plants, about 3" deep, can help
prevent organic material from causing the disease. The pea gravel
also prevents heaving in the winter.