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KPOV – The Point
Gardening: Get Good At It
“Growing Lilacs and Irises”
August 4, 2015
In the spring, have you ever driven past a long-abandoned homesite and wondered at
the huge lilac plants growing in the rubble of an old foundation? If you look closer, you
may also see irises, still flowering among the tall grasses and brush. I like to think a
pioneer woman carried the sapling and the tubers over the long Oregon Trail to her new
home, bringing some of the life she left so far behind.
My garden has both irises and lilacs - I appreciate long lasting plants and love the color
and fragrance of these two traditionals. Planted in a sunny bed, they both seem very
happy to be the first blooms to appear after a cold winter. Since lilacs need such little
attention and irises can grow undisturbed for almost 5 years, they’re perfect for a lazy
gardener like me!
Most people know the bearded iris but there are more 200 types of iris including some
North American natives. They grow either from rhizomes or bulbs. The bearded iris and
the Siberian iris grow from rhizomes. The Dutch and the reticulate iris grow from bulbs,
planted in the fall. While bearded irises are easy-to-grow, long- lived perennials, they
need to be divided every 3 to 5 years. Now is a good time to plant, divide & transplant
iris since they like hot, dry weather. If not divided, the plants become overcrowded and
flower production decreases.
Plant irises in fertile, well-drained soils with 6 or more hours of sun. The best flower
display will have at least 3 tubers in a group.
To divide irises, first cut back the leaves to about one third their height, lift the entire
clump & use a sharp knife to separate the rhizomes. Replant them about 18” apart with
the tuberous rhizome just below the soil, untangling the roots beneath the rhizome as
you go. The irises should be in full bloom by the second year.
I really love lilacs because they’re hardy and long-lived, requiring only a minimum of
care. From the first bud color to the fading of the flowers, common lilacs, Syringa
vulgaris, typically bloom for 2 or 3 weeks. If you plant several species, you might have
blooming plants for at least six weeks. They thrive in sunny sites with well-drained soil
but don’t plant lilacs against warm, light-colored walls that could cause the flowers to
bud too soon and die in a late frost.
New shoots sprouting from the roots keep lilacs young. If you dig up a lilac sucker &
include some roots, the transplant will be a clone of the original plant.
If your lilac never flowers, the problem could be
 a shady location (maybe overhanging tree branches need to be cut back),
 or - it’s a young plant - less than 7 years old (just be patient),
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or - it was feed too much nitrogen (be sure the lawn fertilizer isn’t falling under
the lilac),
or - it was pruned just before flowering, removing the buds. (Always prune lilacs
immediately after the flowers fade),
or - the shrub might need a renewal pruning to encourage blooms on younger
branches and discourage insects. (Remove about a third of the older branches
every year).
I love the heart-shaped lilac leaves but some people think the plant looks unkempt after
blooming. If you’re in that group, plant your lilac at the back of a sunny bed and enjoy
the blooms before the rest of the shrubs leaf out.
For more information on growing lilacs and irises or any other gardening topic, call the
Master Gardeners at 541-548-6088 or visit our website: gocomga.com and click on the
KPOV tab on the orange bar. This has been Gardening: Get Good At It on KPOV: The
Point.
Resources
Iris publications:
http://www.ipm.iastate.edu/ipm/hortnews/1993/6-30-1993/iris.html
“Siberian Iris” - http://www.gardening.cornell.edu/homegardening/scene51d1.html
“Time to Divide Iris” - https://web.extension.illinois.edu/cfiv/homeowners/000722.html
Lilac publications:
Montana State University Extension MontGuide: MT199805AG: Growing Lilacs in Montana.pdf
(includes a detailed table rating hybid lilac varieties)
“Growing Lilacs: - https://web.extension.illinois.edu/cfiv/homeowners/020511.html
“Growing Lilacs” pdf document http://extension.unh.edu/resources/resource/591/Growing_Lilacs
“Lilacs” pdf document - WSU Extension, Spokane County