Lazy Gardener’s Guide: How to Grow Irises

grow irises

Irises are a favorite of mine. The pop of color from the irises always brings a smile to my face! The best part about growing irises is that it is effortless. As a self-confessed lazy gardener, I like irises because they are one of the easiest and most beautiful flowers you can grow in your yard. Once your irises are established, you don’t even have to water your irises! It never ceases to amaze me every year how something so beautiful can be so easy to grow. I don’t have a sprinkler system and I never water my irises (their only water source is natural rainfall!) yet my irises grow back every year! And each year, the irises grow back bigger than the previous year. Below you will find everything you need to know on how to grow irises and how to propagate irises (trust me, it’s easy to propagate irises!)

Basic Facts on How to Grow Irises

Are Irises ANNUAL or PERENNIAL?

Irises are perennial plants. Irises grow back every year. The best part about irises is they grow back beautifully every year- effortlessly!

Do Irises grow best in SUN or SHADE?

Irises grow best in a location with full sun. Ideally pick a spot in your yard that receives 6-8 hours of sun to grow your irises. As sun-loving plants, irises like a lot of sun especially if the temperature is cool or cold. While it will tolerate or even love some shade during warm weather temperature; too much shade will cut back on the bloom production by retarding the ripening of rhizomes during summer months. Find a sunny spot in the garden and your irises will grow happily there!

What type of SOIL is best for Irises?

Irises prefer neutral to slightly acidic soil. Irises also like soil with good drainage and loose soil. Irises will do well in soil from light sand to clay but will rot if sitting in water saturated soil. Although, I have to confess, as a lazy gardener, I don’t do anything to my soil all year long to improve drainage and yet my irises still grow!

Are Irises DEER RESISTANT?

Irises are deer resistant. I have first hand experience that deers don’t really like irises. My backyard is often visited by a families of deer and I’ve never seen them munch on my irises!

Are Irises DROUGHT RESISTANT?

Irises are drought resistant plants. Once your irises are established in your yard, your irises don’t need to be watered. Irises can survive from just rainfall alone. As a lazy gardener, I love no-fuss, drought resistant plants like irises!

How TALL do Irises grow?

Depending on the types of irises you grow, irises can grow 8 to 60 inches tall and 18 inches wide. Bearded irises can reach 2 to 3 feet in height.

When do Irises BLOOM?

Irises bloom late spring to early summer. Some bearded irises are remontant meaning they can rebloom and will usually flower again late summer or Fall. You can encourage your irises to rebloom with organic fertilizer like earthworm castings and live earthworm.

What USDA HARDINESS ZONE is best to grow Irises?

Irises will grow in USDA hardiness zones 3-9. I live in USDA hardiness zone 7 in coastal Connecticut and have successfully grown irises for almost a decade now.

Step by Step Guide on How to Plant Irises

Below you will find step by step on how to easily plant your irises

  1. Find a Sunny Spot: Finding a sunny location is the most important step to growing irises. Set yourself for success by planting your irises in a sunny location. Irises are sun-loving plants so make sure to find a spot that gets at least 6-8 hours sun.
  2. Space Out Your Irises: Plant iris rhizomes 1 to 2 feet apart. Make sure there is good air circulation around the iris plants. Also, shade the newly planted rhizomes during hot weather to prevent sun from scalding and eventual rotting the plant.
  3. Don’t dig too deep: Dig a shallow hole and make a mound in the center of the hole, the mound should be in level with the surrounding soil, set the rhizome horizontally on the mound and spread the roots down over it. Then fill the hole with soil, firmly press around the roots and water. Leave the rhizomes partly uncovered and visible on top unless the climate is hot. Planting on raised bedding is advisable if the soil is heavy. 
  4. Water Thoroughly: Make sure to water your newly planted irises thoroughly. Continue watering your newly planted irises until the first good rain. If there is a lack of rain, continue watering and make sure your watering is deep enough. Remember with irises, deep watering is better than frequent shallow watering.
  5. Apply fertilizer to newly planted irises: Incorporate alfalfa pellets (without salt) to the soil of newly planted irises.

When Is the Best Time to Plant Irises?

The best time to plant irises is between early July to end of October. Plant irises when nightime temperature is above 40 to 50 degree farenheit. It’s important to plant your iris four to six weeks before the first freeze.

grow irises

How Often Should You Water Irises?

For newly planted iris rhizomes, you need to water your irises daily so the roots will develop. With established irises, you don’t really need to water daily since irises are drought resistant. Over watering irises is worst than under watering irises. Irises can survive with just rain water alone. Of course, if you are experiencing an extended drought or especially dry summers, you can always water your iris plants when the soil looks extremely dry. When you do water your irises, water deep so the root system gets watered.

What type of Fertilizer Should You Use on Irises?

When fertilizing your iris plants, use a well-balanced fertilizer with ratio of 10-10-10 or 5-10-10 (NPK ratio). Don’t use fertilizers with high nitrogen levels on your irises.

When Should You Apply Fertilizers to Irises?

Early Spring is a good time to apply fertilizers to your irises, afterwards, you can apply fertilizers again a month after bloom. When applying fertilizers to your irises, don’t apply fertilizers directly to the rhizomes, just lightly apply fertilizers around the rhizomes.

Troubleshooting Irises with Pest Problems

Symptom of iris borer is brown streaks found on leaves. To fix the problem; dig rhizomes of affected plant and dip the rhizomes with the whole plant in a solution of 1 part chlorine bleach to 4 parts water.  Iris borer are only occasional. Fungal disease is another problem, this can be dealt with by dusting the affected rhizomes with sulfur powder or other fungicide that will not kill earthworms.

When Should You Divide Irises?

Irises will become crowded after 3 to 5 years. Your overcrowded irises will benefit from dividing. Another way to know when it’s time to divide your irises is when you start noticing your iris plants not blooming as many flowers as previous years. If you notice reduced flowers, then it is time to divide your irises. The best time to divide spring flowering irises is usually late summer. This gives the rhizomes enough time to establish a good root system before winter.

How to Divide Irises

Below you will find step by step instruction on how to divide your irises. Dividing your irises will help your irises grow happily.

Step 1: Start by trimming the foliage of your iris plant back to 8 to 12 inches making it easy to handle the iris plant.

Step 2: Use a garden fork and shovel to lift the iris rhizome clump together with the roots out of the ground. I like to use a garden knife to help make it easier to divide irises. If the soil is dry, water your iris plant the day before dividing or right before dividing your iris plant. Examine the iris rhizomes carefully for disease, if fungal disease is noticed, dust the rhizomes with sulfur or other fungicide before replanting.

Step 3: Cut healthy iris rhizomes into pieces, which is usually along the exterior area of the rhizome clump, making sure that each piece should contain at least one fan leaves. You may discard old, woody pieces of iris rhizomes or plant them in a corner.

Step 4: Replant the divided healthy iris rhizomes immediately. Set the divided iris rhizomes right at the soil’s surface so that their tops are partially visible or thinly covered with soil. Use well-drained soil so that the rhizomes won’t rot. If you are replanting your irises in the same plot where the irises were dug out, you can improve your soil by mixing plenty of organic matter such as compost and earthworm castings. It’s also beneficial to add live earthworm into the soil before you plant your irises.

How to Re-Bloom Irises within a Year

Irises normally blooms in the spring, but some irises, if treated very well by giving them an extra dose of organic fertilizer like earthworm castings and live earthworm will rebloom. Watering regularly, especially during summer dry spells will help your iris to rebloom during autumn. Not all irises have the capability to rebloom. Bearded irises will rebloom again from late summer into fall. The following iris varieties will rebloom the second time in the year during autumn: purple-and-white ‘autumn tryst’, bright yellow ‘harvest of memories’, silvery white ‘lo ho silver’, pale yellow ‘baby blessed’, and pure white ‘immortality’.

bearded iris

Types of Irises to Grow

There are two types of Irises. One type of iris are rhizomes classified under Rhizomatous Iris. The other type of iris are true bulb irises classified under Bulbous Iris.

Rhizomatous Iris

Irises whose bulbs are Rhizomes are not true bulb irises. The Rhizomatous irises have flat, sword-like, leaves or foliage that overlap each other to form a fan shaped foliage. It may either have the showy bearded flowers or beardless flowers.

Tall bearded iris

Tall bearded iris have large, wide-petal blooms on branching stems that are two and a half to four foot tall. There are tall bearded iris that are reblooming or remontant type. These variety of bearded irises that rebloom will flower again during summer, autumn or winter.

bearded iris
Bearded Iris

Medium and Dwarf irises

Medium iris have flowers that are similar to the tall bearded iris except the flower size is smaller in proportion when compared to the flowers of the tall bearded iris. There are four basic types of medium and dwarf irises:

  • Border bearded iris: The Border bearded iris is approximately half the size of the tall bearded iris, its stems are around 15 to 28 inches high.
  • Miniature tall bearded iris: The stem of miniature tall bearded irises are the same height as border bearded irises. Though its stem is the same height as the border bearded iris, its stem is pencil-thin-like with tiny flowers of 2 to 3 inches width, it has more stems per clump, limited colors, and same bloom time as the tall bearded iris. 
  • Standard dwarf bearded iris: Standard dwarf bearded irises are basically a cross between tall bearded iris varieties and miniature dwarf varieties, its flowers are around 2 to 3 inches in width.
  • Intermediate bearded iris: Intermediate bearded iris are basically a cross between tall bearded varieties and standard dwarf varieties, its flowers are around 3 to 5 inches in width.
  • Miniature dwarf bearded iris: True to its name, miniature dwarf bearded iris are the shortest of all the irises on earth, it is around 2 to 10 inches in height. Well established miniature dwarf bearded iris plants can produce a rich volumes of blooms. 

Exotic Aril & Aribred iris

The aril’s name comes from the collar-like white cap or aril on their seeds.

  • Oncocyclus iris: The oncocyclus iris have large flowers- 4 to 7 inches in width. The oncocyclus iris flowers come in a variety of colors consisting of gold, silver, lavender, maroon and gray. Stems are around 1 foot in height.
  • Regelias iris: Regelias iris have smaller blooms than oncocyclus iris. The stem size of regelias iris is 1.5 to 2.5 feet in height.
  • Oncogelias iris: Oncogelias iris is a hybrid of oncocyclus iris and regelias iris.

Beardless iris

The flower of beardless irises have no beard on the falls. The roots of beardless iris are more fibrous than fleshy. Some varieties of beardless iris are Japanese iris, Louisiana iris, Siberian iris and Spuria iris.

Bulbous Iris

Bulbous Iris bulbs are more bulb-like than rhizome-like, its leaves are fan like, grasser and rounder in cross section.

Dutch iris

Dutch iris are hybrids developed by the Dutch from several Mediterranean species. They are hardy to –10 degree F/ -23 degree C.

Spanish iris

Spanish iris is a species native to Spain. Spanish iris is similar in appearance to the Dutch iris except that it is shorter, slimmer and has smaller flowers and blooms 2 weeks later than the Dutch iris.

English iris

English iris was first grown as an ornamental plant in England. English iris flower stems reach 1.5 feet tall with two velvet-textured blooms of maroon, blue-purple, blue or mauve. English iris flowers look like Dutch irises though a bit larger with broader falls. 

Reticulata iris

Reticulata iris has a netted outer covering on the bulbs, the plant is slim and small, usually below 8 inches tall.

How to Use Organic Soil Mix and Earthworms to Grow Irises

If you are looking to improve the quality of soil for your irises, you can try the following simple mixture below for your irises. Then you can add live earthworms to help your irises grow!

1 part peat moss

1 part other organic material such as earthworm castings, compost, leaf mold or nitrogen stabilized bark

1 part builders’ sand

Mix the above organic materials to amend your soil. Plant your irises and water thoroughly. Dig a small ½ inch hole beside the planted area the day after planting and put a dozen live earthworms into it, then cover the earthworm with soil so that birds won’t come and pick them up right away. The introduction of earthworm castings or earthworm itself into the surrounding soil of the iris plant will give you years of blooms each year.

Fact Sheet: How to Grow Irises

SIZE:                8 to 60 inches tall, 18 inches wide.

BLOOM:           Spring, summer, autumn, winter

LIGHT:             Sunny,  filtered sun, light or part shade during hot summer.

TIME:               Plant iris bulb in spring or iris rhizomes between mid-summer to mid-autumn.

COLORS:          Almost every color including multicolor.

SOIL:                Average well drained soil

DEPTH:            Depending on particular species

HARDINESS:    Heat tolerance- AHS zones 9 to 1; Cold tolerance- USDA zones 3 to 9

PESTS:             Iris Borer

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