Bulbs - Knowledgebase Question

Brunswick, Ma
Question by eschenberger
March 9, 2010
I have tried and tried to get Iris growing I never get any to come up. I follow the instructions but not luck

Answer from NGA
March 9, 2010


You may be planting at the wrong time of year, or planting them too deeply. The best time to plant iris is late summer through early fall (mid-July until mid-October). Spring planting is discouraged but can be done under abnormal circumstances. Spring planting can often result in lack of bloom for a season or two and slow establishment.

For best growth and bloom, iris need at least half a day of full sun and they need a balanced, well-drained soil but are adaptable to a variety of soil types. Raised beds can help with drainage and are a must for areas with high rainfall. Iris, like most perennials, prefer neutral to slightly acidic soil (pH of 6.8 - 7.0 is ideal). Heavy clays need to be amended with gypsum or coarse sand to aid drainage. You can dig or till the soil to a depth of 10-12" and add a dash of superphosphate or bone meal prior to planting. Iris can be mulched lightly (for winter protection and weed control) as long as the mulch does not cover the rhizome. Once winter is over, you should remove the mulch.

The most common mistake made with bearded iris is planting too deep. First make a 3" deep depression about 6" in diameter. In the center make a small, fist-sized mound of soil. Place the rhizome on top of the mound so that 1/3 of the rhizome will be above the soil. Spread the roots out to support the plant, replace the soil, firmly pack around the roots to remove air pockets and water liberally. We suggest 14-18" as a good distance between rhizomes. This allows the new growth to fill the area between plants in about three to four years. For mass or clump style plantings, plant rhizomes in a triangular fashion about 6? apart. Planting in this way will require division more often than other methods.

Fertilize in mid to late April with bone meal, superphosphate, or a fertilizer low in nitrogen such as 6-10-10. Fertilizers high in nitrogen tend to cause bacterial rot and lush, but weak, foliage growth. When selecting fertilizers for irises, be sure that the 2nd and 3rd numbers are bigger than the 1st. These numbers stand for the amounts of phosphorus and potassium in the mixture. Phosphorus and potassium are the key nutrients in root and bloom production. Another dose of fertilizer at half strength after fall dividing and planting will slow release throughout the winter and early spring. Though fertilizing can only help, it is certainly not necessary for growing a garden of beautiful irises.

I hope these growing tips help you become more successful with your irises.

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