How to Grow Iris

Co-authored by Lauren Kurtz

Last Updated: February 25, 2023 References Approved

Irises are perfect for beginner gardeners and experienced green thumbs alike! The hardy flowers are not difficult to grow and do well in a wide range of climates, being relatively drought-tolerant and low maintenance.^{[1]
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Research source} When it blooms, the Iris's flowers are gorgeous, ranging in hue from the common purple shade to patterned white and yellow. Irises are among the easiest perennials to start and grow, so start planting today for long-lasting blooms.

Part 1

Part 1 of 3:

Planting a New Iris

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Choose a suitable species of iris. Though nearly all irises are fairly hardy and easy to maintain, some are more suitable for certain conditions than others. Depending on the climate and conditions where you plan on planting your irises, one variety may be a better choice. Below is information on just a few of the most common iris varieties:^{[2]
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- Siberian Iris: Despite its name, native to Central and Eastern Europe and Turkey. One of the most adaptable irises — very easy to grow and maintain. Do especially well in temperate climates.^{[3]
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- Louisiana Iris: Native to the hot, humid southeastern United States. In spite of this, grows well in a wide variety of conditions. However, they will not bloom well if they receive less than an inch of water or so during hot growing season months.^{[4]
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- Beardless Iris: Native to Central and Southern Europe. Do well with at least half a day of full sun. Can even survive constant sun though this is not necessarily preferable.
2
Plant in late summer. Most Irises are best planted in late summer (early fall at the latest). This gives the iris a chance to establish its roots while there is still enough sunlight to fuel its growth so that it can survive the winter. For most Iris varieties, July and August are the best months for planting.^{[5]
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- Note, however, that in areas with long summers and mild winters, you can get away with planting irises as late as September or even October — in these cases, there's usually still enough sunlight to help the plant grow its roots before winter.
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3
Pick a spot with about six to eight hours of full sun per day. Most irises thrive if given generous amounts of sunlight. You won't necessarily want your iris to be in constant sun (though they can still do well in these situations), but they can usually stand more sun than similarly-sized flowers. Try planting your irises in a flowerbed that receives the shade of a tree late in the day or on the side of your house that the sun hits in the afternoon for a good amount of light.
4
Plant in slightly acidic soil with good drainage. Irises prefer soils that are neutral to slightly acidic — a pH of about 6.8-7.0 is best. In addition, irises require soil with a good amount of aeration and drainage.^{[6]
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Research source} This is important for preventing root rot, which irises can be susceptible to if over-watered.
- For heavy, clay-rich soils with bad drainage, try adding humus or organic matter to improve the permeability of the soil.
- Planting on a slope or in a raised flower bed can help with drainage — in these cases, water will naturally run away from the iris.
5
Plant the rhizome so that its top is exposed. One common mistake first-timers make when planting irises is to plant them too deep. Unlike most plants, irises do best when their rhizome — the brown, root-like structure at their base resembling a potato — is slightly exposed to the air. The plant's roots should be arranged so that they spread downward beneath the rhizome.
- Note that in very hot climates, covering the rhizomes with a thin layer of dirt (no more than an inch or so) can help protect them from drying out.
6
Plant the rhizomes so that they are spaced apart. More so than other flowers, irises have a tendency to grow together when they're planted near one another. When this happens, the plants can compete for the same soil, water and nutrients, hampering each others' growth. To prevent this, try to plant your irises' rhizomes at least one to two feet apart.^{[7]
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- Even with this preventative measure, after a few years, your irises may grow together anyway. If this happens, don't worry — you can fix this by simply digging up some of the rhizomes and replanting them farther away to "thin out" your flowers.
7
If the growing conditions are unfavorable, pot the iris. Depending on where you live and what time of the year it is, conditions outdoors may not be suitable for growing new plants. Rather than plant your irises in the soil outside when they're not likely to do well, instead, get them started in a pot. This allows you to carefully control the amount of time that the plants are exposed to the weather outside until it improves and you can transfer them to the garden. If conditions are very bad, like, for instance, if there's heavy frost, you can even keep the plants indoors 24/7.
- For most irises, a 12-inch pot will work well. Exceptionally small irises can do well in 6-to-8-inch pots.
- Regardless of the size of pot you use, make sure it has good drainage — at least one big hole on the bottom (or several smaller ones) for the water to drain out of.

Part 2

Part 2 of 3:

Caring for a Growing Iris

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Water generously after planting. After you plant your irises, give them a thorough watering. If conditions are dry, water every 7 to 10 days or as needed during the morning or evening.^{[8]
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Research source} Assuming you planted your irises in the late summer or early fall, you may stop watering your plants as soon as the weather cools and it begins raining or snowing.
- One common mistake to avoid with your irises is over-watering. If the rhizome or roots are held in contact with moisture without being given a chance to drain, root rot can set in. This fungal condition can be potentially fatal for the iris and easily spreads to nearby plants, so prevention is key.^{[9]
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2
Taper watering off as the plant becomes established. Over time, your plant will require less and less watering on your part. Once the weather takes a turn for the cooler in the fall, you can stop watering until the next summer growing season. In general, your iris should require less watering with each subsequent summer — for climates with mild summers, it's possible
- The exception here is for areas with very hot, dry summers. In these cases, some watering may be necessary every summer to keep the iris from drying out. Though irises are quite durable, they can't survive in extreme conditions without help.
3
Keep rhizomes uncovered and roots well-aerated. As the iris grows, you'll want to periodically check to make sure that the rhizome hasn't become covered with dirt, organic matter, or other debris. If it has, gently brush it off without moving the plant itself or disturbing its roots. In addition, make sure that the soil still has good aeration and drainage — if it doesn't, add humus or organic matter as needed.
4
Trim brown or dying leaf matter and the flower stalk. Unlike high-maintenance garden plants, iris leaves don't require pruning or trimming for good growth. In fact, leaving the leaves undisturbed even after the growing season allows the iris to gain more nutrients from photosynthesis for next year's growth.^{[10]
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Research source} In general, the only sort of trimming you should need to do for iris leaves is to remove brown, dead leaf tissue that has already died — this provides no benefit to the plant.
- Note that, before winter, you may also want to cut the flower stalk to its base. If the flower dies during winter and falls at the base of the plant, it can cause rot to spread to the rhizome as it decays.

Part 3

Part 3 of 3:

Maintaining an Iris Year-Round

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Protect the plants in preparation for winter. As the plant's roots establish themselves throughout the late summer and early fall, you may want to put some thought to how you plan to protect your irises once the weather grows cold, especially if you live in an area with exceptionally cold winters. Snowfall can naturally protect the soil from the cracking and heaving that can occur during very cold weather and dislodge the rhizomes.^{[11]
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- If your area doesn't reliably get snowfall, you may want to spread a loose mulch (like evergreen bough) across the ground to protect the soil. Don't apply a thick layer of mulch — this can actually trap moisture in the soil and cause rot.
- Destroy any irises exposed to heavy frost — left to rot, these plants can become havens for borer eggs.^{[12]
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Weed and protect against pests in the spring. As the weather begins to warm, you can allow any snow to melt naturally and/or remove any protective mulches you used in the winter. As new plants begin to sprout up, keep a keen eye out for any weeds near your irises and pull them out as early as possible. Use environmentally-friendly herbicides or weed killers to keep grasses and weed away from the bases of your irises.
- In addition, you'll want to be wary of any encroaching pests, especially slugs. There are many, many ways to bait slugs, from commercial products to improvised home solutions. One very easy way to do this is to make a beer trap — fill a wide-mouthed jar halfway up with beer and bury it up to the rim of the jar in the soil. Slugs, attracted to the beer, will fall in and drown.^{[13]
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3
Monitor growth and give nutrients in the spring. Irises can benefit from the occasional light application of fertilizer starting the growing season after you plant it. Don't use a fertilizer high in nitrogen — this can cause excessive foliage growth (and, eventually, rot). Water after dispensing the fertilizer to avoid fertilizer "burn". Below is a selection of fertilizers that are acceptable to use with irises:^{[14]
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- General purpose "5-10-10" fertilizer
- General purpose "5-10-5" fertilizer
- Bone meal
- Superphosphate
4
Repeat the cycle as needed! As the iris grows more mature, the amount of time you'll need to spend maintaining it should decrease drastically. Still, even when your plant has been established for years, it's a good idea to give it a check up every few weeks just to ensure that there are no problems with it. As long as the plant is receiving good sun during the growing season, occasional rainwater, and nutrients from the soil, it should be just fine. Irises are perennials, and they'll gradually spread from the roots over many growing seasons.
- Every three to five years, you’ll want to divide the irises in crowded flower beds and replant them to avoid competition for water and soil.^{[15]
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Expert Q&A
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Question

Do iris plants need full sun?

Maggie Moran
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Maggie Moran is a Professional Gardener in Pennsylvania.

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Yes. Iris plants need a minimum of between 6-8 hours of direct sunlight each day.
Question

When should you plant iris bulbs?

Maggie Moran
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Maggie Moran is a Professional Gardener in Pennsylvania.

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It is best to plant iris bulbs in late summer or very early in the fall. This would be between July and September in the U.S.
Question

How do you plant iris?

Maggie Moran
Home & Garden Specialist
Maggie Moran is a Professional Gardener in Pennsylvania.

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Home & Garden Specialist

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Ensure it is in well-drained soil and has as a minimum of 6-8 hours of direct sunlight per day. An additive of Gypsum is a great way to improve the soil quality.