Gardeners – American Iris Society (2024)

Iris are generally discussed in two groups: Bearded and Beardless.

Bearded have a fuzzy beard on the fall (the bloom part that hangs down). Beardless do no have this. Their cultural requirements are different although both can be easily integrated into your existing garden.

Irises are among the easiest of perennials to grow, and they give an abundance of beauty with minimum care. The iris has a thick fleshy root called a “rhizome” (pronounced rye-zome) about like a tough potato in texture. When you buy a new iris, you will probably receive a rhizome with clipped roots and leaves. It can remain out of the ground for a week or two without serious harm, but the sooner it is planted, the better.

To plant your bearded irises, choose a sunny spot in well drained soil. Prepare the soil well, by spading or turning over the soil with a garden fork to a depth of at least 10 inches. Spread fertilizer and work it into the top of the soil. If possible, this should be done 2 to 3 weeks before you are ready to plant. A well prepared bed will result in better growth and more bloom. Don’t starve your irises or make them compete with nearby grass or weeds for food and water. Many gardeners, iris and otherwise, have soil analyses made of their garden soil, then add the fertilizer of the kind and quantity the tests show the soil needs.

The soil should be light. If it is clay soil, add very coarse sand and humus. Bone meal and a good garden fertilizer, low in nitrogen, are good for irises, but manure should be used only after it has aged for about a year. Otherwise, it may cause rot. The roots must be buried firmly to hold the plant in place, but the rhizome should be near the surface. An easy way to achieve this is to dig two trenches with a ridge between them, place the rhizome on the ridge and spread the roots carefully in the trenches. Be sure to firm the soil tightly and allow enough for settling to keep the rhizome above any possible standing water. Then fill the trenches with soil, letting the top surface of the rhizome be just barely beneath the surface of the soil.

If you have several plants, plant them at least a foot and a half apart, “facing” the same way. The rhizomes will then increase in the same direction, without crowding each other too soon.

From the new parts of the rhizome, new bloom stalks will come up in later years and the flowers will be exactly as the original flower. This is called “vegetative propagation”.

In about 2 or 3 years, the new rhizomes will begin to crowd each other and you will want to divide the plant, cutting the newer parts of the rhizome free from the old, which may then be discarded. Unlike the other bearded irises, arils need to be transplanted annually.

You will have so many new rhizomes that you will share them with your friends. Perhaps you received your first rhizomes from a friend. When digging, keep all plants carefully labeled with their names, for sure identification. It is wise to keep diagrams of your planting area to double check individual labels on the plants.

This digging and separating is best done between one and two months after bloom season, usually in July or August. Soon after this the irises grow roots which help to hold the plant firmly during the winter in areas where freezing and thawing can result in heaving the rhizome out of the ground. If you live in this type of climate, a mulch of salt hay can be very beneficial.

Culture of the beardless irises differs somewhat from culture of the bearded irises. They should be transplanted in the fall or in early spring. The roots shouldneverbe allowed to dry out while they are out of the ground and they should be watered heavily after transplanting. They should be set slightly deeper than the tall bearded.

Japanese iris should be planted in a distinct “depression” in heavy soil to assist in supplying moisture to the plant.

Siberians and the Pacific Coast Natives can tolerate light shade but the Spurias, Japanese and Louisianas demand full sun.

Louisianas and Japanese require moist conditions during the summer months while the Pacific Coast Natives enjoy a very low humidity and dry soil no matter how hot it may get. All, except Louisianas, should be planted in a permanent spot where they can remain for many years as they resent being disturbed. Louisianas are strong and quick growers and therefore, should be tended to every few years. All are heavy feeders and need to be fertilized regularly.

Contemporary Views by Perry Dyer

Gardeners – American Iris Society (2024)

FAQs

Should iris rhizomes be soaked before planting? ›

Bare root rhizomes should be soaked briefly before planting. Iris reticulata and Iris histrioides bulbs can be planted much more closely together at 10cm (4in) apart and 7cm (3in) deep. You can add a mulch of organic matter each spring (but avoid contact with the exposed rhizomes as it could lead to rot).

How often do irises need to be watered? ›

Once established you should reduce the watering until the winter or fall rains set in. During dry spells (over three or four weeks long) you will need to give them a good deep watering every 3 to 4 weeks depending on the temperature. The second time the Iris needs water is in the early spring.

How long can iris rhizomes stay out of the ground? ›

Now lay the “keeper” rhizomes aside in a shaded location, a garage or cool shed is a good storage area, while the planting beds or plant- ing holes are readied. It will not damage the prepared rhizomes to remain out of the ground for two weeks.

What is the secret to growing irises? ›

For the best bloom, plant iris in a sunny location. If your climate is on the hot side, some shade is acceptable. Almost all irises need well-drained soil but there are some species that prefer more moisture than others. The ideal soil for irises is slightly acidic but irises are quite adaptable pH-wise.

What month is best to plant irises? ›

When, Where and How to Plant Bearded Iris Rhizomes: For best results, Iris should be planted in July, August or September. It's imperative that the roots of newly planted Iris be well-established before the growing season ends. In areas with hot summers and mild winters, September or October planting may be preferred.

How deep should I plant my iris rhizomes? ›

Prepare garden bed by loosening soil to a depth of 12 to 15 inches. Mix in a 2 to 4 inch layer of compost. Dig a shallow hole that is large enough to accommodate the rhizome or clump of rhizomes. The hole should be about 10 inches in diameter and about 4 inches deep.

Are coffee grounds good for irises? ›

Coffee Grounds in Soil

The issue with coffee grounds is that even though they are rich in nitrogen, they are high in acidity and caffeine. Thus, some recommend them only as an additive to soil for acid friendly plants (ex: blueberries, holly, azaleas, Japanese iris).

How do you keep iris blooming all summer? ›

Reblooming irises perform best if fertilized again after the first wave of flowering is finished. Do not overwater irises; too much moisture in the soil can cause the rhizomes to rot. Water consistently and deeply, especially during summer drought. Keep rhizomes exposed.

What is the best fertilizer for irises? ›

The American Iris Society recommends using a 'well-balanced fertilizer with an N-P-K ratio of 10-10-10 or 5-10-10', highlighting both superphosphate and alfalfa pellets as very beneficial products for feeding irises.

How many years do iris plants last? ›

Multiplying perpetually, there is no limit on a bearded iris' lifespan. They rarely if ever need fertilizer. They tolerate a wide range of soil types. In dry-summer climates they're highly resistant to disease.

Should iris bulbs be covered with dirt? ›

That depends. In light-textured soils, it can be covered by as much as one inch of soil, but for average to heavier soils, the top of the rhizome is best left exposed to the healthful influences of sun and air. Remember that the rhizome is a stem, not a root, and needs to breathe!…

How deep do you bury iris bulbs? ›

But how deep do you plant iris bulbs exactly? Plant the bulbs in holes 4” deep and 2” - 4” apart; for larger groups, dig out a trench, position the bulbs, then replace the soil and water them well.

Should I put mulch around irises? ›

Iris however also need very good drainage and resent being covered with mulch, so do not mulch over top of the rhizomes or you may invite rot. Iris need to be reset every three years or so when they become crowded.

What do you put around irises? ›

If weeds are your concern, plant the iris and then place a 3"-4" layer of organic mulch over the bed. The mulch will suppress weeds, help the soil hold moisture, and make digging and dividing your iris (every 3-4 years) a much more pleasant experience.

How many iris bulbs should I plant together? ›

Generally, bearded irises are planted 12-18 inches apart, with the fan of leaves facing the same direction. If you have multiple cultivars, plant the different types in groups of three to seven rhizomes. After planting, water your iris and keep the soil moist (but not too wet) until new leaves begin to emerge.

How do you prepare iris bulbs for planting? ›

Planting
  1. Step 1 - Choose a healthy plant / cut leaves back to 6" (15cm) ...
  2. Step 2 - Make a mound. ...
  3. Step 3- Place rhizome on top - Splay roots around the mound. ...
  4. Step 4 - Back fill to leave top half of rhizome exposed to sun. ...
  5. Step 5 - Plant in groups of three (same variety) / allow plants to 'breathe'

How do you rehydrate iris rhizomes? ›

Cover rhizomes with one inch of soil where the white-green division line on the rhizome is. Plant about 24 inches apart and give them an inch of water the first time, then 1/2 to 3/4 inches of water per week until new growth appears.

How long to soak bulbs before planting? ›

Planting Guidelines For Spring Planted Bulbs by Variety. Planting depth: Plant 5" deep. Soak bulbs for 2 hours in luke warm water before planting.

How long to soak iris seeds before planting? ›

Iris seeds can be planted at any time, but the best time to plant the seeds is during the fall/winter/ and VERY early spring months. First, soak the seeds in water (using a pudding bowl, cup, or similar) for at least 48 hours up to 2 weeks.

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