Dividing Irises

The month of September has rolled by quickly, and I am somewhat behind on my monthly garden task list.  September is a great time to divide and re-plant irises.  I have some beautiful white irises that need a little more room, and I will be moving some of them to a new spot in my yard.

Iris beds do well if you have thin them every two or three years.  Irises are rhizomes, which means it has a stem that grows horizontally just under the surface of the soil.  This creeping, underground stem will sprout stems and leaves upward and roots downward.  Thinning helps to promote new growth and blooms.

If you need to divide your irises this year, select a sunny, well-drained area in your yard.  I have grown irises in part shade before, but they do like to have well-drained soil.  Too much water will cause the rhizomes to rot.  If your yard does not drain water well, consider planting your irises in a raised bed.

Before digging your existing irises, cut the leaves back to one-third the full height.  Dig under the clump of rhizomes and lift the whole clump out at once.  Iris rhizomes grow close to the soil surface, and it is easy to dig them up.  Cut the rhizomes into sections.  Each section will need at least one growing point (fan of leaves), a few inches of rhizome, and some roots.  Discard any mushy or diseased rhizomes.  Be sure to keep a solution of disinfectant nearby and clean your pruning shears if you cut into a diseased rhizome.  A disinfectant solution can be one part bleach and nine parts water.  Cover with a thin layer of soil, just enough to cover the roots and lightly cover the rhizome.

Irises do not need much water.  Water thoroughly after planting, but the plants should not need additional water unless we experience a prolonged drought.  Irises do not need much maintenance throughout the year.  Trimming the leaves is only recommended when you divide irises.  The foliage is used to build up food reserves for flowering the next spring, so trimming established plants will reduce their ability to store energy.

Irises have an interesting history, and you can find some neat varieties at old homesteads and gardens.  Most gardeners are glad to share their extra irises when they start dividing and replanting, so check around if you’d like a source of free plants!

For more information about lawn and garden topics, contact Kate Whitney, Williamson County Horticulture Extension Agent, at 512-943-3300.

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