Summary: Learn how to grow fine iris plants with these simple tips, including preparing the soil, fertilizing, ensuring proper drainage, and managing diseases and pests to achieve a stunning display of irises in your garden.
If you expect iris plants to arrive this month, you’ll want to warmly welcome them. Give them a bed adequately prepared, good soil, and correct planting. (6 Tips for Getting Iris Off To A Good Start.) If you already own some that have finished blooming, they deserve thanks for lifting and dividing or other care.
- Iris plants prefer well-drained soil rich in humus and a moderate amount of complete fertilizer.
- Good drainage is essential for healthy iris growth; raised beds can help improve drainage in heavy soil.
- Diseases like rhizome rot and fungus leaf spot can be managed through proper care and preventative measures.
- The iris borer is a common pest that can be controlled with regular spraying of Malathion.
- Various types of irises, such as bearded, Siberian, Japanese, Louisiana, and Vesper irises, offer a wide range of colors and growth habits.
Iris like good soil with plenty of humus and a reasonable amount of iris plant food. The ideal soil is where 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.
Preparing the Soil for Irises
Where this is not available, you can recondition with compost, old cow manure, or dry manure with superphosphate and bonemeal added.
As soon as the iris 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 the roots.
Growing iris in a garden of mixed plants presents a slightly different cultural problem from that of iris grown in nursery beds, mainly feeding irises. 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.
Fertilizing Iris Plants
Many growers shun fertilizers with high nitrogen content. It produces soft growth, which tends to increase rhizome rot. We use “commercial” fertilizer of 4-8-7 or 5-10-10 ratio each spring during the 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 amounts of bonemeal and superphosphate are applied in about the same proportions. These feedings are the same as those given to the public garden.
Perfect drainage for iris is essential.
Related: How To Lengthen The Iris Flowering Season
Ensuring Proper Drainage For Iris Soil
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.
Fibrous roots should be well spread out; the rhizome should 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 taste.
We make over iris that need it immediately after blooming, and we mulch for the winter all those planted in the current season with pine needles, vermiculite, or salt hay. The leaves are not covered. Mulching of established clumps is not imperative but seems beneficial in our Massachusetts climate. We apply the mulch just before freezing weather is expected.
Managing Diseases and Pests
In New England, most growers have to combat two diseases, rhizome rot and fungus leaf spot, and one serious iris pest, the iris borer. Scorch and mustard seed fungus diseases prevalent elsewhere rarely occur here.
Decay 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 the rotted area is cut off when it does occur.
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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.
Controlling the Iris Borer
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.
After that, spraying must be done once a week until blooming time. It is 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 rush must be present to intercept them.
Following bloom, the clumps must be inspected, and crowded ones divided and reset. Most iris varieties need division every two or three years, or the rhizomes overgrow, starvation begins, and disease is introduced. Intervals between necessary divisions depend on the varieties, and the spacing is given to them at planting time.
Types of Irises and Their Characteristics
Bearded Irises get their name from the thick line of fine hairs lining the outer petals or falls. Beardless Iris, lack these hairs. They flower throughout the United States and often are the main garden attraction.
There are endless possibilities for combining different varieties for a unique garden effect. Light colors tend to stand out more than dark colors. Planting a few well-chosen varieties in clumps can create a more impactful display.
Irises have surface rhizomes and broad, sword-shaped leaves. Their flowers come in a range of sizes and colors, blooming in May and June. They prefer a sunny, well-drained location but can also grow and flower in partial shade. They need good cultivation to achieve the best results.
Siberian Irises, which bloom in early June, are known for their flat, open flowers on tall, slender stems. These Irises come in white and various shades of blue and range in height from two to four feet.
They thrive in naturalized areas near streams or open meadows. They also grow well under ordinary garden conditions. Plant them in spring and divide them when the clumps become too big.
When Japanese Irises blooms in July, they display large, gorgeous flowers in various shades of white, lavender, deep purple, blue, lavender-pink, and more.
These Irises have been grown for centuries in Japan. They need rich soil that is moist in summer but not wet in winter. They are many named varieties. The best plan is to buy them by sight or grow them from seed.
Louisiana Swamp Irises, also known as Beardless Irises. They represent species and hybrids of these species, both natural and artificial. They occur in bogs and swamps in Louisiana but thrive in other regions with the right conditions. The flower color range is extraordinary, and they grow under a wide variety of conditions.
They grow much further north than their native range. For the best results, they need soil rich in humus and plenty of water during their growing season. During the winter, they need drier conditions.
In the south, light shade is a plus. In the North, they grow best in full sunshine. Many fine-named iris hybrids are available. Both hybrids and species of Louisiana Iris have adapted for gardens in warm climates.
Iris Dichotoma (Vesper Iris)
When growing the Vesper Iris (Iris dichotoma) you can set your watch! The vesper blooms from late July to frost at 3 PM every day. With selective breeding plants are now taller and produce more flowers than in the past.
The bright-colored flowers are arranged in a candelabrum-like branching pattern. The plant is easy to grow and thrives in a variety of soils and in partial sun. It is hardy and can survive winters without protection.
It is ideal for impatient gardeners as it:
- Multiplies rapidly
- Blooms soon after planting
- Is a paradise for pollinators
- Is great for gardeners looking for something different.
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