Fertilizing Iris #749885 - Ask Extension

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Fertilizing Iris #749885

Asked May 14, 2021, 10:20 AM EDT

I grow tall bearded iris. In the past I have purchased 6-24-24 fertilizer from Anderson Garden's in Forest Lake. I apply the fertilizer by hand, sprinkling it on the plants, then making sure is is not on the rhizome. Can you comment on this type and method of application? Flugel's in Rosemount sells a similar fertilizer. 9-23-30 Would that be an acceptable substitution? Thanks for your thoughts. Christine Ploetz Roseville MN chris.ploetz@hotmsil.com

Ramsey County Minnesota

Expert Response

All sources I have found recommend that the nitrogen (first number) be small.  A 6-10-10 or bone meal might be better.  Here is a copied paragraph from a commercial iris farm: FERTILIZATION - Modern iris varieties may need more fertilizer than older varieties due to the increased number and size of blossoms. We fertilize in mid to late April with bone meal, superphosphate, or a fertilizer low in nitrogen such as 6-10-10. Fertilizers high in nitrogen tend to cause bacterial rot and lush, but weak, foliage growth. When selecting fertilizers for irises, be sure that the 2nd and 3rd numbers are bigger than the 1st. These numbers stand for the amounts of phosphorus and potassium in the mixture. Phosphorus and potassium are the key nutrients in root and bloom production. Another dose of fertilizer at half strength after fall dividing and planting will slow release throughout the winter and early spring. Though fertilizing can only help, it is certainly not necessary for growing a garden of beautiful irises.

Barbara Harlan Replied May 14, 2021, 2:57 PM EDT

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