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Ask a Master Gardener: Irises that won’t bloom may be planted too deep

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A variety of factors could causes irises not to bloom. (Submitted photo)

Q: I have some Irises that have been in the ground for five years and never bloomed. They are in full sun and on an irrigation system that waters daily. What am I doing wrong?

A: It can take a little time for a plant to bloom after being transplanted, but five years is ridiculous. There are a few reasons why iris don’t bloom. Maybe one will fit your plants.

The most common reason is not enough sun, but you seem to have that covered. They need at least six hours of sun.

Iris need to be planted high. The top of the rhizome should be visible. Don’t mulch over the rhizome; it should always be exposed or it can rot or act out by refusing to bloom.

They need a little fertilizer, but too much, especially too much nitrogen, causes lots of leaf growth at the expense of flowers. This happens with most flowers. A soil test would give you fertilizer recommendations for your specific soil and plants.

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Over-watering might be a problem. Daily watering is seldom a good idea, whether for grass or garden beds. The exception is during hot, dry spells like we just had when potted plants may need daily or twice-daily watering, and freshly planted items might need water daily or every other day. But normal watering should be less often and deeper. Frequent watering causes shallow roots that cannot handle dry spells or other stressors. Or it rots roots.

Iris should be watered when the soil is dry to about three inches. So, you may want to change your irrigation settings to water longer once a week or so. In our mild climate many established iris seldom need watering.

Iris need to be divided every three to five years. By that time, they should have spread, with the middle part crowded out, and bloom reduced. Even if yours have never bloomed, healthy plants should have spread.

Since yours have never bloomed, I would dig them up, look at the roots, and check the rhizomes for rot or other issues. The American Iris Society has good pictured instructions on how they should look and how to replant at irises.org .

Now, this was all assuming your irises are tall bearded. Some kinds of iris, such as the native blueflag, can grow in very wet conditions. But my guess is yours are suffering from too much water, are planted too deep, or are over-fertilized.

Written by U of M Extension Master Gardeners in St. Louis County. Send questions to features@duluthnews.com.

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Related Topics: HOME AND GARDENGARDENING
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