Fewer Iris blooms?

Did winter affect Irises?

By: Sandy Feather 2014
Penn State Extension

Q. I have a large bed of irises that also has touch-me-nots and coreopsis. This year, very few of the irises bloomed, although they grew to their normal size and looked healthy. They are not too crowded. Did the winter weather affect it as it did other plants, or do I need to fertilize them? What kind of fertilizer should I use? Due to the other plants in the bed, it would be difficult to work fertilizer into the soil.

A. You do not say which kind of iris you are growing, but tall bearded and Siberian irises bloom best in full sun at least six hours a day and evenly moist, well-drained soil. Irises do not seem to have taken the hit that many other plants suffered this past winter. However, there are other factors that keep them from blooming well.

Iris bloom

Are your irises not overgrown because you divided them recently? If so, they may take a growing season to re-establish and reach blooming size again. Also, irises prefer to be planted very shallowly, with the rhizomes just at the soil surface. If they are planted too deeply, they produce all leaves and few or no flowers. Do not mulch over the rhizomes, as mulch can hold too much moisture and cause them to rot.


Competition for the Iris?

Although the irises are not overgrown, are the other plants in the bed impinging on their space? Touch-me-nots (Impatiens spp.) can grow quite tall, and they may be casting shade on your irises, and competing with them for moisture and nutrients. If you do not have room to apply fertilizer because there are so many plants in the bed, it may be time thin out the touch-me-nots and coreopsis.

Are soil deficiencies affecting the Irises?

Fertilization may be helpful but should be based on a soil test. That is the only way to tell for sure what nutrients are lacking and how much of which fertilizer will correct the deficiency. Be careful with high-nitrogen fertilizers, because they push lush foliage growth and no flowers. Soil test kits are available from your local Penn State Extension office. In Allegheny County, soil test kits are $12 for the first kit and $9 for additional kits ordered at the same time. They come with instructions for taking a good soil sample and understanding your results. Make checks payable to Penn State Extension and send to Soil Test Kit, Penn State Extension, 400 N. Lexington St., third floor, Pittsburgh, PA 15208.


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