Fertilizing Iris

Iris is a wonderful ornamental plant in the garden that supplies a long period of flowers with very little maintenance from the gardener required. A simple plan for fertilizing all types of irises encourages a healthy root system and larger and longer-lasting flowers during the blooming period. Irises thrive in neutral pH soil and do not require more than one or two applications of fertilizer a year. 


How To Fertilize Iris

Irises of all types thrive in neutral soils with low levels of nitrogen. Nitrogen is needed to keep the foliage robust and reliably green, although high levels of this macronutrient encourage heavy leaf development. Profuse foliage often attracts aphids and other sap-sucking pests to attack the new growth. If left untreated the plant can suffer from abnormal growth and flowering. 

Irises appreciate a granular, slow-release fertilizer applied before and after the normal blooming period. Spread the fertilizer in a ring around the plant, near the root zone, and avoid getting the feed on the rhizome or foliage. Gently scratch the fertilizer into the top layer of the soil and water the root zone well. Every time the plant is watered, some of the fertilizer will wash into the soil and be available to the root system. 


Best Time To Fertilize Iris

Fertilize irises twice a year. First, apply feed as the new growth emerges in the spring before the flower buds form. Feed again directly after the plant has finished flowering. The second feeding helps prepare the plant for better blooming in the next year.  

Best Fertilizer For Iris

Slow-release fertilizers are great for feeding perennials planted in the ground. They slowly release nutrients at every watering and last for up to 3 months or more. Iris will perform best with a low NPK ratio around 1-2-2. Look for organic fertilizers marketed for blooming perennials or tomatoes and roses. Dr. Earth Rose and Flower Food has a good ratio of NPK and is a sustainable way to feed ornamental plants.

Iris Fertilizing Tips

  • Low-nitrogen fertilizer encourages blooming without excess foliage
  • Feed iris with a slow-release fertilizer 
  • Apply the fertilizer one month before flowering and again directly after flowering is finished


-Always wear protective gloves and a face mask when handling chemical fertilizers.

-Closely follow all directions and storage guidelines that are on the fertilizer label.


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 Author Robbin Small - Published 4-18-2023