For the Love of Iris

Articles, Tips and Notes from Schreiner's Iris Gardens

The “Scoop” on Fertilizing Iris


Customers often ask us, “How and when should I fertilizer my iris?”Fertilizer_NewBag2018web2 

The short answer (continue reading for the nitty-gritty): one month before bloom season, while the tulips are blooming, apply a low-nitrogen, well-balanced fertilizer, such as Schreiner’s 6-10-10 Controlled Release Iris Food. Keep the fertilizer several inches away from the rhizomes. In late September, fertilize again. That sums it up nicely, but perhaps you would like a bit more to chew on about the “what” and “when” of feeding your Iris. Read on for a more substantial serving of info on nurturing both your soil and your Iris.

There are four main nutrients that we must maintain in the soil: nitrogen, phosphorus, potassium, and calcium. The first three nutrients are found in most mixed fertilizers, and calcium can be purchased separately in the form of limestone. Nitrogen is necessary for new cell formation in all parts of a plant. Compared to other nutrients, nitrogen is typically the most lacking. A symptom of a shortage of nitrogen is yellow-green stunted growth. Potassium (potash) is necessary for strong roots and stems as well as deep flower color. A symptom of potash deficiency is weak stems and yellowing or browning leaf tips and edges. Phosphorus is necessary for development of roots and stems. This nutrient also stimulates fruit and seed production. A symptom of Phosphorus deficiency is red or purple discoloration of leaves.

Before applying any fertilizer to your garden, do a soil test to discover what your plants actually need. The best way to know how much, and at what proportion, to add nutrients to the soil is with a soil test. Simple soil tests can be purchased at garden supply centers. Once you determine what nutrients are lacking or are in abundance, you can amend the soil to correct most problems. Your soil test may also reveal a need to correct pH or add trace minerals, for example. Completing a soil test, and making modifications to your soil based on the results, is the preferred method to determine fertilizer amounts.

Fertilization of Iris is important to obtain best results, but must be done in moderation. The only thing Iris may resent more than underfeeding is overfeeding. Nitrogen, potash, and phosphorus are essential for Iris, but excessive nitrogen promotes lush growth that is more susceptible to rot diseases. If applied in concentrated form, do not allow the fertilizer to come in direct contact with foliage and roots, as the plant may be damaged or killed. Low-nitrogen fertilizers, such as 6-10-10, are ideal for the needs of Iris.

When to apply fertilizer to Iris:

1)   In the spring, about a month before bloom, apply a light application of fertilizer around the Iris clumps. This goes for dwarf iris, too, which bloom in March. Apply a low-Nitrogen fertilizer to your dwarf iris in mid to late February. Apply the same to your intermediate and tall bearded iris in intervals coinciding with the month before their bloom cycles.

2)  At planting, sprinkle a tablespoon of the fertilizer around the newly planted rhizome. Or, if preparing a large area for iris planting, incorporate ½ lb of a low-nitrogen fertilizer such as 6-10-10 per 50 ft2 (or 1 ½ oz per 10 ft2) to your garden bed.

3)  After your Iris bloom is another time you should fertilize them. Doing so keeps them healthy and in tiptop shape for better growth for the growing cycle later in the year. Wait a month or so after blooms have finished, or in the fall, with enough time before winter so the Iris have the proper nutrition they need going into their winter dormancy.

Now that you’ve got the scoop on Iris nourishment, you can take the necessary action to feed your hungry Iris. Schreiner’s Gardens offers a specially formulated Iris food to help you provide balanced nutrition in the flower garden. Order now for summer and fall shipment.

Happy gardening!

Information sourced from:


Author: Schreiner's Iris Gardens

Growing beauty since 1925. Retail and wholesale supplier of high-quality Bearded Iris & Daylilies.

15 thoughts on “The “Scoop” on Fertilizing Iris

  1. Would you give me information regarding the separation of irises. How do I tell which part will bloom the following year, and do you just throw the other part away or will it multiply? My mother ordered from your company for years but I just never got that information from her.


  2. I have my iris in pots and most are coming up just fine. I watched the segment on garden time. I covered the roots with bark mulch in the fall. Now that they are growing should I take off some to expose the rhizomes?


  3. Thank you so very much, this was very helpful to me , I was like 😩Now I’m like 😁


  4. I like dry fertilizer to absorb in and feed my plants. With iris’s I did not know about the 2 feedings a day. I just got 4 more Iris plants before winter but did not get them in the ground. Any chance you think I can save them? They are just sitting in the containers, frozen on top my lawn in Minneapolis Minnesota , so super cold.


    • Oh my! Our apologies for the extremely delayed reply! We do not recommend 2 feedings per day on Iris. We recommend one feeding in the spring, about the time the tulips are blooming in your neighborhood; then another about one month after bloom is done. If you are planting new Iris in the summer, or dividing older clumps in the summer, that is also a good time to add a little low-nitrogen fertilizer to the newly planted Iris. Bone meal also works well with Iris. Thank you for the comment. Please accept our apologies for the oversight. We hope you had a glorious bloom season!


  5. Excellent web site yyou have here.. It’s difficulkt to find quality writing like yours these days.
    I seriously appreciate people like you! Take care!!


  6. How much area will a bag of the fertilizer cover? How is it applied? The article says IF applied in concentrated form – does that mean that it can be dissolved in water and applied generally over the iris bed, without fear of damaging the rhizomes? If so, in what concentration? How much dry product to how much water? How about a hose-end sprayer? I would greatly appreciate another article with more in-depth information regarding the actual application of the fertilizer, and I suspect many others might feel the same.


    • Thank you for the great questions. By “concentrated form”, we are referring to a granular type that is not designed to be diluted. If you choose to use the type of fertilizer that is to be diluted, we suggest you follow the manufacturer’s recommendations for ratio and method of application. The fertilizer that we sell is granular and should not make direct contact with the rhizomes. Sprinkle one tablespoon per rhizome onto the soil surrounding the plant and gently work into the soil. Water after applying. We will post more information about applying our Iris food soon. All the best!


      • Well, as much as I’d prefer to use your product, I think I’ll have to use something that can be diluted. I have three very large iris beds, with a total of nearly two hundred plants. At my age, and arthritic state, I don’t think I can do the “work into the soil” routine too well. Thanks for the reply, and happy gardening!


      • Although we do recommend to work the fertilizer into the soil, the fertilizer can still be effective if simply sprinkled on the soil around the plants and then watered in. Perhaps give a package of our product a try. Regardless, we wish you all the best and great happiness in your gardening. We welcome you to share a photo of your amazing collection in bloom next May!


      • A little more on the topic of dry vs. liquid fertilizer: A fellow local Iris breeder had the following to add to the conversation. Because of the waxy leaf surface [of Iris], not sure how efficient foliar feed would be [e.g., a liquid sprayed on through a hose attachment], but any fertilizer taken up by the roots would have to be in liquid form, such as the dry granules which become available when we water and the plant dines on fertilizer soup. Hope that helps!


  7. Thanks for the article about fertilizing iris. I knew about low nitrogen fertilizer and not using too much, but your information about the timing of the two feedings really helped!


  8. How about potasium capsels, crushed? I have lots of them and they are hard to swallow.


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