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Planting, Growing, and Caring for Irises
Planting
Irises bloom best in full sun, meaning at least 6 to 8 hours of sunlight daily. They can tolerate as little as half a day of sun, but it鈥檚 not ideal. Without enough light, they won鈥檛 bloom well. Bearded irises must not be shaded out by other plants; many do best in a special bed.
Provide well-draining, fertile, neutral to slightly acidic soil. Loosen the soil to 12 to 15 inches deep, then mix in compost or aged manure. Good drainage is critical: Irises prefer 鈥渨et feet, but dry knees.鈥 They will not tolerate wet soil in winter. Learn more about preparing the soil for planting and organic soil amendments.
When to Plant Irises
- Plant most irises in late summer to early fall, when nighttime temperatures remain between 40掳 and 50掳F (4掳 and 10掳C) or above. This gives them plenty of time to get established before the coming winter.
- Tall bearded iris varieties are best planted closer to fall because they tend to go dormant in early to mid-summer.
- If you receive bare rhizomes or irises in a container at some point earlier in the year, plant them as soon as possible. It鈥檚 better to get them in the ground rather than wait until the 鈥渋deal鈥 time.
How to Plant Irises
- Plant bare-root rhizomes (the thick stems) horizontally, with the top exposed and only the roots underground. In areas with particularly hot summers, set the rhizome just below the soil surface.
- Dig a hole 10 inches in diameter and 4 inches deep. Make a ridge of soil down the middle and place the rhizome on the ridge, spreading the roots down both sides. Fill in the hole and firm it gently, leaving part of the rhizome and the foliage uncovered.
- Plant singly or in groups of three, 1 to 2 feet apart, depending on the fully grown plant鈥檚 size.
- Soak Siberian iris rhizomes in water overnight before planting, then set them 1 inch deep (2 inches, if the soil is sandy), 2 feet apart. Over a period of years, they will form clumps; divide when blooms get smaller and vigor declines.
- Do not mulch around the rhizome, as this may encourage rot.
- Water thoroughly.
Growing
How to Grow Irises
- In the early spring, remove winter mulch and old foliage to allow for fresh growth.
- Fertilize in early spring, scratching an all-purpose fertilizer around the plants. Avoid high-nitrogen fertilizers. 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. Unlike bulbs, which thrive deep underground, bearded iris rhizomes need a bit of sun and air to dry them out. If they鈥檙e covered with soil or crowded by other plants, they鈥檒l rot.
- Taller irises may need staking, or they will fall over.
- Deadhead (remove spent blooms) consistently. Bearded Irises flower sequentially on buds spaced along the stems.
- After blooming is finished, cut flower stems down to their base to discourage rhizome rot, but do NOT trim the iris鈥 leaves. The plant鈥檚 foliage carries on with photosynthesis and generates energy for next year鈥檚 growth and flowers. Only prune off brown leaf tips, if desired.
- After a hard frost in the fall, cut foliage back hard, remove any foliage that appears spotted or yellowed, and dispose of all debris in the trash.
- If iris foliage is hit with heavy frost, remove and destroy it to eliminate borer eggs. See your local frost dates.
- For winter protection, cover the rhizomes with an inch or two of sand topped with a light layer of evergreen boughs, applied after the ground freezes and removed when the forsythias bloom in the following spring.
- Iris borer, a common iris pest, overwinters as eggs in spent leaves. Signs include vertical streaks in the leaves. If apparent, look for the pests and squash them! If you see rot in the rhizome, dig it up and remove the affected parts. See pest tips below.
Dividing Irises
Over time, it鈥檚 not unusual for plantings of irises to become overcrowded, which causes the rhizomes to lose vitality and stop blooming. When this happens (usually every 2 to 5 years), it鈥檚 time to divide and replant healthy rhizomes in fresh soil.
When to divide? Do this task after flowering finishes, and then trim the foliage back to six inches.
- Shortly after blooming (usually around midsummer), carefully dig up (lift) the clump of irises. You鈥檒l find that the original rhizome that you planted (the 鈥渕other鈥) has produced several offshoot rhizomes.
- Separate these rhizomes from the mother with a sharp knife and discard the mother, as it will no longer produce blooms.
- Inspect the rhizomes for any rotting tissue, soft spots, or other signs of disease, removing and discarding infected parts or entire unhealthy rhizomes.
- Plant these fresh rhizomes in a new bed, replant them where they were before (after adding new soil), or share them with friends and spread the joy of irises!
Types
The tall bearded irises, Iris germanica, come in many flamboyant colors. They are generally planted in the fall. Rebloomers (remontant) varieties include:
- 鈥业尘尘辞谤迟补濒颈迟测鈥: fragrant white flowers that appear in early summer and again in late summer; hardy to Zone 4
- 鈥楩eed Back鈥: fragrant dark purple flowers; Zones 4 to 9
- 鈥楨arl of Essex鈥: white flowers, with purple edging; Zones 3 to 10
- 鈥楯ennifer Rebecca鈥: mauve pink flowers; Zones 4 to 9
Credit: Pixabay
Siberian irises, I. sibirica, also come in a range of colors. They have a more delicate beauty than the stately bearded irises, but are equally as rugged. They also tend to be more pest and disease resistant.
- 鈥楤lueberry Fair鈥: ruffled blue flowers; Zones 3 to 8
- 鈥楩ond Kiss鈥: white flowers with pink flush; Zones 3 to 8
Credit: Pixabay.
Japanese irises, I. ensata, bear huge, flat blooms. These heavy feeders thrive on moisture during the growing season and do well around ponds; move to drier ground for fall and winter.
- 鈥楥辞丑辞鈥: pink flowers with golden flush; Zones 4 to 9
- 鈥榁补谤颈别驳补迟补鈥: dark purple-reddish flowers; Zones 4 to 9
Credit: Pixabay.
Catherine Boeckmann
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I'm confused. I have a box of 10 Tall Iris Hollandica Mixture bulbs (extra large size), and the box states that I should be planting between April-June for the Toronto, Ontario area after the danger of frost has passed. In reviewing the information on your website, you recommend that bulbs be planted in the fall, so I need clarification on when I should be planting these bulbs, spring or fall?
Our guidance above suggests planting in mid to late summer. (Not sure where you’re seeing 鈥渇all鈥 on this page.) We do not know where you purchased yours/what brand they are but we checked a few experts and they suggests that [Dutch] Iris Hollandica be planted in fall鈥攍ike daffodils and tulips. (Like those bulbs, these iris are expected to bloom in early spring.) We can see how a conflict could develop. As a final answer, we recommend following the guidance on the iris container. Presumably, that is the truest advice. If you have any further questions, perhaps there is a source and contact mentioned on the packaging?
I happened upon a box of iris bulbs (they aren't rhizomes, but bulbs like tulips) on sale at a big box store. Without thinking, I planted them in large containers a few days ago. They were starting to sprout when I planted them. Then I found out I should have waited until Fall to plant them. Should I dig them up now? Or leave them where they are. They've received a fair amount of water, since we've had some rain since i planted them. Thanks.
I just found and bought today a set of Miss Saigon bulbs. When I got home I began to wonder if it's already too warm for them to grow and bloom. Days here in the Tampa Bay area are already in the 80s. Should I just hold onto them for later in the year? I'm able to find much information about bulb planting this far south. Our days never really get "cold"...
As Dutch Irises (like 鈥楳iss Saigon鈥) tend to bloom from late March to early June, it would probably be best to hold onto your bulbs and plant them in late fall, when it’s (hopefully) a little cooler.
My iris dividing turned out almost all white blooms when the rhizomes originated from plants of several other colors..... need to know is there a tip or trick to fix this problem?
I planted a variety of colors, purple, yellow and white. They are ALL white when they bloomed. I dug them myself from my parents supply. Why would they change color? I really wanted Purple and some yellow.
We have beautiful plants but very few blooms. Any suggestions?
There are several common problems that could be preventing your irises from blooming:
- Overcrowding: Irises that are clumped too tightly together may stop blooming and will benefit greatly from being divided. Simply dig your irises up鈥攂eing careful to leave most roots intact鈥攁nd separate the plants鈥 rhizomes from one another with a sharp blade. Each division should consist of a sizable rhizome, several roots, and at least one fan of foliage. The best time to divide and replant irises is mid-summer, as this gives the irises a good chance to reestablish themselves and (hopefully) bloom in subsequent springs. Freshly replanted irises should be given ample water for several weeks after they are planted.
- Lack of sunlight: Irises bloom best when they receive at least half a day (6 hours) of full sun. If your irises are receiving too little light, they may not flower.
- Over-fertilization: Too much nitrogen can encourage irises to grow foliage instead of flowers. Lawn fertilizers contain large amounts of nitrogen, so avoid exposing irises to these.
- Too much or too little water: Irises prefer well-draining soil, so make sure your irises are not getting swamped with water, which can lead to root or rhizome rot. Irises do not need to be planted very deep in the ground and should be allowed to dry out a little before their next watering. Depending on your local climate, irises can be watered once or twice a month in the summer.
Dealing with one or more of the above issues should get your irises back to blooming. Good luck!
This week I dug up a plethora of iris from a flower bed at my church that will be bulldozed in mid-May due to construction. These iris should bloom in late May and have nice long leaves and the beginnings of emerging buds on a few. If I transplant them now in my garden, in mid-April, will they bloom? Or should I store them and wait to plant in the fall? I live in the Eastern shore of Maryland.
