What Kind of Fertilizer to Use on African Iris?

Soil Enrichment

• Though African irises tolerate poor soil, they much prefer fertile, well-draining soil rich with organic matter. For best results, incorporate organic materials into the soil before planting your African irises. Usually, 3 inches of peat moss, 3 inches of compost and 1 inch of perlite is sufficient to enrich the soil and improve its drainage; till the organic matter into the soil to a depth of 6 inches. The African irises absorb nutrients from these materials and use them to form an extensive root system in their new location.

Mulching

• Mulching the soil around African irises is beneficial for the plants in many ways. A thick layer of organic mulch helps the soil to retain moisture, which is particularly helpful during the spring and summer, when African irises are actively growing and blooming. It also inhibits the growth of unwanted vegetation at the planting site, reducing the need for weeding. As the mulch decomposes, it acts as a slow-release fertilizer, providing the African irises with a steady stream of essential nutrients.

Chemical Fertilizers

• African irises require at least two applications of fertilizer each growing season to ensure they have the nutrients necessary to produce their showy blossoms. Apply the first application in the early spring, before your African irises present new growth; use a balanced, water-soluble fertilizer, applied according to label instructions. Fertilize African irises a second time when they start to set their buds; this time, use a water-soluble high-phosphorus fertilizer.

Organic Fertilizers

• African irises also respond well to organic fertilization methods. Feed your plants with an application of leaf-mold, aged-manure, bone-meal or alfalfa-meal fertilizer in the early spring. Once the African irises start to set flower buds, apply a single application of a high-phosphorus organic fertilizer, such as ground rock phosphate or guano phosphate. Always apply fertilizer products according to the application instructions on the packaging; though organic, an excess of fertilizer can still damage your plants.