The vibrant and elegant blooms of irises are lovely and learning how to fertilize iris properly can produce spectacular results. While irises aren’t particularly fragile plants, they do need to be cared for properly for a full season of colorful flowers.
When to Fertilize
Irises should be fertilized in the early spring. To make sure they have the right amount of nutrients for the best blooming results, fertilize them shortly before their blooming season. Irises that are malnourished may be stunted and fail to produce blooms. Irises should receive another feeding in the fall, before winter hits. This will help protect the plants throughout the winter. If your irises are showing signs of poor health or malnutrition, they may need a bit more fertilizer. Check the roots of the iris. If the soil has been damp, you may have rotten roots. By gently removing the damaged roots, replacing the plant and fertilizing, you can revive the plant.
Choosing a Fertilizer
Irises should be fertilized with 5-10-10 or 5-10-5 fertilizer, about 1 to 2 tablespoons. Do not apply the fertilizer directly onto the rhizome, as it can burn the delicate roots. Manure and other high-nitrogen fertilizers are not recommended for fertilizing irises as they can contribute to rhizome rot. Bone meal is also recommended to be applied when the irises are planted. This is a slow-release source of phosphate. Triple phosphate and other rapid-release phosphate options can burn the rhizomes and are not recommended.
How to Apply Fertilizer
The fertilizer should be gently dusted around and in between the plants. Heavy application is not necessary and may damage the plants.