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Bearded Iris and How to Plant Them

Maria is a master gardener and master of public health. She & her husband, known online as The Gardener & The Cook, live in coastal Alabama.

A Little Trivia about the Bearded Iris

There are over 300 species in the genus. The one most familiar to most of us is the tall (at least 28 inches) bearded iris. It's the royal standard (fleur-de-lis) of France, and is also the symbol of Florence, Italy.

These exotic-looking flowers have three large outer petals called “falls” and three inner upright petals called “standards.” The falls have beards or crests. Bearded iris are called this because of the soft hairs along the center of the falls. In crested iris, the hairs form a comb or ridge.

Depending on where you live, your irises will flower in early-to-mid spring or early summer. Some, mostly hybrids of the bearded type, will bloom again in late summer.

What We’ll Cover Here

  • When and where to plant
  • How to plant
  • How to fertilize
  • How to protect from rot

When and Where to Plant Bearded Iris

The best time to plant or transplant these beauties is anytime between July and September, but it’s typically so hot here in Zone 8a during those months, that I don't want to work outdoors, so I usually wait until October or even November.

Always position your iris beds on higher ground that is not likely to flood or have standing water, but not on a steep slope, as it will allow soil and mulch or fallen leaves to be washed over the rhizomes, essentially making them deeper and more likely to rot. That's what has happened to the iris in the photo below, and even though it appears healthy now, it's roots are slowly dying.

This iris was planted on a slope that was pretty steep, and soil has washed onto the rhizome, essentially putting it underground.

This iris was planted on a slope that was pretty steep, and soil has washed onto the rhizome, essentially putting it underground.

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How to Plant

  • Loosen the soil to a depth of about 10-to-12 inches, then mix in 2 to 4 inches of compost.
  • Bearded irises have rhizomes (fleshy roots) that should be mostly exposed.
  • Plant the rhizomes singly or in groups of three with the fans toward the outside of the group, and 1 to 2 feet apart, depending on the size of the rhizome.
  • Dig a shallow hole 8 to 10 inches in diameter and 3 to 4 inches deep. Make a little ridge or mound of soil in the middle and place the rhizome on the ridge, spreading the roots on both sides. Fill the hole with soil to cover the long roots, and gently press until it is firmly in place. After doing this, I usually lift up slightly on the plant, then press the soil down around the rhizome again. When you’re done, water thoroughly.
This group of irises needs to be cleaned by removing the dead leaves, separating the pups from the main plant.

This group of irises needs to be cleaned by removing the dead leaves, separating the pups from the main plant.

How to Fertilize

The best fertilizer for flowering (and fruiting — think tomatoes) is with a high middle number (phosphorus, a.k.a., potash). Look for a fertilizer with the numbers 2-8-4 or 5-8-4 or 8-15-8 – something like that. The high phosphorus content promotes strong roots and increases productivity, that is, flowering and fruiting.

Be sure to avoid applying high-nitrogen fertilizers, as this will result in lush leaves, but will not help the flowers. Nitrogen is always the first number. To learn more about fertilizers and the three numbers, check out my article entitled Organic vs. Chemical Fertilizers, and Those 3 Little Numbers.

Beautiful re-blooming bearded iris

Beautiful re-blooming bearded iris

How to Protect From Rot

  • Plant them in well-drained soil.
  • Avoid mulching on top of the rhizomes with any organic matter, as this will encourage the rhizomes to rot.
  • Be sure to remove any fallen leaves or other yard waste that may drop onto the rhizomes.

In Summary: Bearded Irises Have Only a Few Needs, But Those Needs Are Important

  • Irises need at least half a day (6 hours) of sun, and well-drained soil. Without enough sun, they won’t bloom. Bearded irises should not be shaded by taller flowers or shrubs. Because of this, they don't make good understory plants; and they will do best in a special bed is reserved just for them.
  • They prefer fertile soil, with a neutral to slightly acidic pH. If your soil is very acidic, sweeten it with a bit of lime. When we lived in central Florida, the soil was on the alkaline side, so I had to increase the acidity of the soil. I did this by mulching around them with pine needles, and amending the soil with used coffee grounds.
  • Irises are drought tolerant so, of course, they don't like soggy soil, which can lead to rot. Because of this, good drainage is very important for this and any drought tolerant plant.
  • Bearded irises need some "chill hours". By that, I mean they need the cold winter weather in order to thrive. So, if you live in a tropical or semi-tropical area, bearded irises will not do well.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 MariaMontgomery

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