Tall bearded iris are very easy to grow, requiring little attention and, once established, little watering. They perform best in a sunny position and prefer good drainage. The top of the rhizome should be at soil level so it is exposed to sun and cold, and hence it is important that neither mulch nor other plants be allowed to encroach on the irises' growing area. If the rhizome receives insufficient sun flowering will be affected. If you have a particularly heavy soil the addition of gypsum to improve drainage can be of considerable benefit. Bearded iris allowed to sit in waterlogged soil may develop rhizome rot which can cause the eventual demise of the plant.
Clumps should be divided every three or four years to prevent overcrowding and a subsequent reduction in flowering. Whilst theoretically iris can be divided at any time of the year, the ideal time to plant out iris rhizomes for optimum flowering the following season is November/December (after flowering) through to March/April though best to avoid the hot summer months if possible.
An autumn and spring feeding of an organic fertilizer such as Rapid Raiser or Dynamic Lifter should satisfy their feeding requirements. A handful of the fertilizer under the roots on planting or replanting is also recommended.
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