How to Grow Irises

We are lucky enough to have some fabulous gardening neighbors. They just drop off whatever they happen to be thinning in their gardens. {We have only been here for 6 months and they already know me so well!} One such neighbor dropped off some irises late last week so I thought I would show you how to plant them. Its fairly straightforward, but there are a few tricks that will make for happier, healthier plants.

Irises are some of the easiest flowering perennials that you can grow. They are both deer resistant and drought tolerant. Irises can be grown in a wide range of zones {3-9} with only a minimum amount of care. With hundreds of varieties in almost every color, and several sizes, they are sure to find a place in everyones garden.

First lets take a look at the parts that make up an iris. Totally complex right?! Knowing these three parts will make some of the descriptions easier to decipher farther down.

Parts of an Iris
For the best blooms choose a location that is in full sun, meaning 6 or more hours per day, with well-drained soil. In hot climates they can handle some afternoon shade. There should never be standing water in the bed. Irises are pretty darn forgiving but they will do best in slightly acidic soils. {a pH of 6.8 is ideal} If the soil is heavy you will want to add organic matter to improve drainage. Work the soil well and deep, at least 12 inches down. It is beneficial to mix well rotted compost in to the soil to feed the irises over time.

One of the most common mistakes is planting irises too deep. {These are not tulip bulbs, people!} The rhizomes need to be partially exposed above the soil surface. The exception would be if you live in a hot and dry climate then you may plant the irises just below the surface but no deeper than 1 inch. You will want to space the plants 1 to 2 feet apart, irises like their space and don’t appreciate being crowded.

To plant an iris: dig a hole about 10 inches wide by 4 inches deep and build up a mound in the middle. The top of the mound should be just about level with the soil surface. Place the rhizome on the mound, with the leaf fan to the outside of the bed, and arrange the roots around the mound. Fill the hole leaving part of the rhizome exposed, and water in thoroughly.

Iris mound
The iris rhizome sitting on top of the mound with it’s roots arranged around it. Fill in the hole leaving part of the rhizome above the soil surface.

In the spring use a balanced fertilizer, like a 10-10-10, but avoid anything with a high nitrogen content. {Nitrogen is the first number and is mainly responsible for the green growth} Apply it lightly AROUND the rhizome but not directly on them. Irises will also benefit from another fertilizer application about a month after they bloom.

Over watering is another common mistake that is made. Once established, you can let the top few inches of soil dry out in-between waterings. Keep in mind that less frequent, deep watering is better than frequent shallow watering.


The amount of blooms will decrease over the years as they become too crowed. Most irises will need to be divided every 2-5 years. The best time to divide and transplant irises is the mid to late summer, soon after they have finished blooming. They go dormant in the heat of the summer around July or August. Go ahead and dig up the whole clump, give them a good wash with the hose and inspect for damage. Discard any rhizomes that are soft or have holes from iris borers. You can then cut or carefully break the rhizomes apart so each piece has at least one fan of leaves. Trim the leaves so you leave about 6 inches intact, this helps reduce the workload on the roots. Follow the directions above to plant the rhizomes back in the same bed or in a new location.

iris borer damage
Over all irises are hardy but they do have one arch-nemisis, the iris borer. The iris borer hatches as tiny caterpillars from eggs that were laid on the leaves the previous year. They then climb up the leaf, bore into it and eventually down into the rhizome. By then they are 1 ½ to 2 inch pinkish caterpillars that can eat large portions of the rhizomes. Check the rhizomes every time you divide them for holes or mushy spots and destroy any iris borers you find. You can minimize the number of borers by cleaning up your iris beds in the fall. After a hard frost remove all of the leaves, stems, and nearby plant debris.

Irises are beautiful, hardy and long lived plants. Every gardener should make room in their garden for this wonderful plant.

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Iris square

3 thoughts on “How to Grow Irises

    1. Hi Frances! Irises require full sun (6-8) hours per day. If you were to plant them in the shade they would probably struggle and never bloom.

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