Iris Flower Fertilizer. 06072020 During the early spring you need to fertilize the irises especially when they begin to grow. During the early growth of bulbs you need a fertilizer rich in phosphorus because it helps in root development and plant growth.
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This is the middle number on the fertilizer bag.
1 In the spring about a month before bloom apply a light application of fertilizer around the Iris clumps. The first number represents the nitrogen content which gives the plant its pretty green leaves. Jen - pardon to all of you who hear me say this often if you have Japanese or Siberian iris do NOT use lime on them as it is poisonous to them. 10052010 Irises grown for competition can be fed again in late summer and mid-autumn with 1 tablespoon of fertilizer.