How to Grow Fine Iris

If you’re expecting iris plants to arrive this month, you’ll want to give them a warm welcome… a bed properly prepared, good soil, correct planting. And if you already own some that have finished blooming, they deserve thanks in the way of lifting and dividing or other care.

We’ve found that our iris like good soil with plenty of humus and a reasonable amount of food. Ideal soil is that in which this flower has not previously been grown. If you’re remaking the bed or replacing older varieties with new ones, try to give them new soil. Where this is not available, you can recondition with compost, old cow manure or dry manure, with superphosphate and bonemeal added.

Perfect Drainage

Perfect drainage is essential. We find that somewhat raised beds help, and we’ve added quantities of humus, compost, old cow manure and sand to lighten our heavy earth and improve drainage still more.

Fibrous roots should be well spread out; the rhizome ought to be placed horizontally, and lightly covered with soil. We set our rhizomes 10 inches apart, with three, five or seven rhizomes in a triangular clump but you may want to use different groupings to create pictures that suit your own taste.

We make over iris that need it immediately after blooming, and we mulch for the winter all those planted the current season with pine needles, vermiculite, , or salt hay. The leaves are not covered. Mulching of established clumps is not imperative, but seems to be beneficial in our climate in Massachusetts. We apply the mulch just before freezing weather is expected.

Feeding Time

As soon as the plants start to grow, either after summer planting or in spring, we give them a moderate amount of complete fertilizer. This is worked into the soil a few inches away from roots.

The growing of iris in a garden of mixed plants presents a slightly different cultural problem from that of iris grown in nursery beds, particularly with regard to feeding. At one time, it was thought that bearded iris required only a small amount of bonemeal which was said to be “safe,” and that no other type of fertilizer was needed. There is, however, a growing tendency to treat them like other plants, with plenty of humus, and reasonable amounts of complete fertilizer.

Fertilizer of high nitrogen content is shunned by many growers. It produces soft growth which tends to increase rhizome rot. We use “commercial” fertilizer of 4-8-7 or 5-10-10 strength, each spring at the time of garden cleanup, and additional nourishment is given after blooming.

Besides the inorganic material, wood ashes and superphosphate are sprinkled around the rhizomes, equal parts with the fertilizer, three pounds to 100 square feet scratched in with a hand weeder. In the fall, equal parts of bonemeal and superphosphate are applied in about the same proportions. These feedings are the same as those given to the general garden.

Diseases and Control

In New England most growers have to combat two diseases, rhizome rot and fungus leafspot, and one serious pest, the iris borer. Scorch and mustard seed fungus disease prevalent elsewhere occur rarely here. Rot is controlled by clean culture and good drainage. We don’t experience it in iris planted on the side of the hill. Raised beds in level areas help in its control, and when it does occur the rot area is cut off.

Fungus leafspot is prevalent during hot, muggy or rainy weather. Weekly spraying with sulfur helps to prevent it. All affected leaves should be removed and destroyed.

We no longer have borers. Weekly spraying of the iris and surrounding areas with Malathion has completely controlled them. The first spray is applied following the first warm period in late March or early April. Spraying must be thorough and it is advisable to remove dead leaves beforehand. Thereafter, spraying must be done once a week until blooming time. It is absolutely necessary to spray regularly and thoroughly, for once borer larvae have entered the iris fans, sprays cannot reach them and they must be destroyed by hand. They hatch at intervals throughout spring, and the spray must be present to intercept them.

Following bloom, the clumps must be inspected and crowded ones divided and reset. Most varieties need division every two or three years, else the rhizomes overgrow, starvation begins, and disease is invited. Intervals between necessary division depend on the varieties, and the spacing given them at planting time.

by IW Fraim

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