FERTILIZER

Bearded iris do not require much fertilizer, but like most plants they need a little food to have stronger plants and nicer blooms. When planting, mix Superphosphate or steamed Bone Meal into the planting spot. Use at a rate of ½ ounce per square foot three weeks before the plants are set in. Half this amount should be used if it is added just before planting time. Once established, use a low nitrogen fertilizer (such as 6-24-24, 13-13-13, 10-20-10, 5-10-10) as a top dressing as plant growth and soil conditions warrants. About one ounce (1 tablespoon) per square foot of 5 -10-10 or similar formulation can be sprinkled in a circle around each clump. It is recommended that iris be fertilized once in early spring when the plants begin to grow and (around the time the crocus bloom). Then they should be feed a second time three weeks after the bloom season is over. After apply fertilizer hose the plants clean to wash off any residue that has fallen on the plant. Depending on how much rain or watering the iris beds receive, sandy soil may require more frequent feedings due to leaching. Fertilize according to the plant’s growth and health. Any fertilizer must be in solution before the plant can us it, so water any granular fertilizer in well. Or dilute any liquid food. Which types of fertilizers is used depends on the recommendations of your county agent based on soil testing, personal preferences and gardening conditions. Do not over fertilize your iris. Over fertilization may lead to soft rot of the rhizomes. Fertilizers high in nitrogen and green manure should be avoided, especially in the fall. Fertilizers high in nitrogen will provide lush green growth in the first year, but can cause soft rot.
Organic compost and aged manures supply very little nutrients (usually about 0.8-0.3-0.6) but are excellent soil conditioners. Alfalfa pellets or meal, well rotted compost or manure can be worked in as a side dressing in early fall.