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Growing Irises

Growing Bearded Iris


Bearded Iris Cultivation


Perennial Iris--All About Iris Gardening 

Tall bearded iris plants are the easiest of perennial garden plants to grow.  Although good results can be achieved with minimal care, the best iris culture will provide a more magnificent display.  Tall bearded irises are a clump-forming perennial of 2-foot high by 2-3 feet around of sword-like leaves.  The bloom stalks will grow above the foliage and display between 6 to 14 flowers.  The large and showy flowers are 6 inches tall.  Each flower has six petals, three upright petals called standards and three semi-flaring pendant petals called falls.


Where to Plant Bearded Iris

Irises would prefer a full day of sun, but a bed that receives a minimum of six hours a day will do.  The irises will survive in less than six hours of sun, but they will not bloom. Irises need to be planted in WELL-DRAINED locations.  If necessary, raise the iris bed slightly to ensure that water does not stand in your beds.  Good air circulation is also essential to prevent foliage diseases and rhizome rot.  The best results are achieved with sunlight and air circulation down to the rhizome.


Soil Preparation

This is the most important factor in growing irises.  A well-prepared iris bed will result in better growth and bloom.  Soil preparation is best done 2 to 3 weeks before planting irises.  Since irises cannot tolerate standing in water, they prefer loose, well-drained soil.  Dig and loosen the soil at least 10-18 inches deep.  Thoroughly break up all lumps.  Irises grow in average garden soils with a pH close to neutral (6.5-6.8).  The addition of compost and fertilizer promotes the very best growth and bloom.  Organic matter improves soil structure and drainage.  Fertilizer enriches the soil.  For new plantings, either well-rotted compost or well-rotted manure is beneficial.  For poor soil, add 1/2 cup of 5-10-5 fertilizer for every 6-7 rhizomes or ½ pound for each 5’ x 10’ area.  Thoroughly mix fertilizer into the soil.  In heavy clay soils, raised beds with lots of compost work best.  Adding sand, compost, or organic material will allow moisture to drain out quickly.  Adding 30 percent coarse sand aids drainage in heavy clay soils.  Agricultural gypsum, if the soil is alkaline, and agricultural lime, if the soil is acid, are also excellent soil conditioners that can help to loosen clay soils.  Perlite or vermiculite added to sandy soils will assist with water retention.

Planting Distance

Spacing iris rhizomes 2 to 3 feet apart allows plants to remain undisturbed for several years.  Spacing rhizomes 12 inches apart in groups of three, forming a triangle with the fans facing out and the toes pointing inwards creates an instant clump effect.  Leave 18” to 24” between each group of three rhizomes.  Irises planted in rows should be spaced 18” apart with all rhizomes facing the same direction so the increases will all grow in the same direction without overcrowding.  Closer spacing will necessitate more frequent dividing. 



Placing a teaspoon of bone meal per each rhizome will ensure your iris grows strong roots, solid rhizomes, and strong plentiful bloom stalks.  Plant your iris rhizome at or just barely below the surface of the ground.  DO NOT PLANT TOO DEEPLY. 


1.    Begin by making a shallow hole that is about twice the size of the rhizome.

2.     Take a handful of the soil and build a mound in the center of the hole.

3.     Position the rhizome on the top of the mound and drape the roots on each side of the mound. 

4.     Firm the soil around the roots and firm the soil tightly around each rhizome.  Air pockets will allow for water to collect and eventually cause rot.

5.     Water newly planted rhizomes thoroughly.

6.     Either label your irises or record the name and location of each iris so you can identify them to your friends when they bloom!

7.     Use straw to mulch in cold winter areas before it snows.  Be sure to remove the mulch after the last hard frost to prevent rot from forming as the ground warms up.

8.     Irises are perennials; they will require time to grow.

If the weather is too hot or too cold, iris rhizomes may be potted until the temperature changes before planting in the ground.  The sooner irises are planted, the better.  Be sure that the pot your select has enough depth to support the roots and that it provides excellent drainage.



Newly set plants need moisture so they can grow a new root system.  They should be kept moist but not waterlogged until the new roots have been established.  This usually takes between 2 to 4 weeks. Four new leaves indicates that the new roots are established.  Once established watering should be reduced until the winter or fall rains set in.  Avoid overhead watering of your irises because this encourages leaf spot.  During dry spells, your irises will benefit from a good deep watering about every 3-4 weeks.  Irises need water every other week during the spring either through spring rains or by supplementing.  Reblooming iris require more frequent watering to encourage the development of blooming stalks and flowers in the summer and fall seasons.




Irises should be fertilized about 6 to 8 weeks before bloom in early spring and again after bloom is finished.  A good way to remember this is to fertilize around Valentine’s Day, mid-March, and in summer.  The summer application helps keep the plants looking good in your garden and is especially important for the reblooming irises.  Use a light balanced fertilizer such as 5-10-10 and bone meal or super phosphate.  It is very important not to use any fertilizer that is high in nitrogen because too much nitrogen can lead to problems with rot.  The fall application is best 0-10-10 and bone meal and superphosphate.  Phosphorous encourages root development and potassium improves the overall health of the iris plant, and helps defend the plant against diseases, as well as helps the iris plant withstand very cold or hot weather.  Apply a light application of fertilizer as a top-dressing dusted around and between plants.


General Garden Care

Keep the garden as clean as possible.  Groom your plants several times a year.  Cut and remove brown, spotted, and damaged leaves.  Discard; do not compost these leaves.  Remove the limp outside foliage as the iris grows.  Keep the rhizome clear of all garden litter, including weeds, grass, and dead iris leaves.  Only the bloom stalks should be cut, not the iris leaves.  Cut the stalks close to the ground.  Do not allow any dead leaves to remain around the plants especially in the winter.


Reblooming Iris Culture


To flower again, rebloomers require a little more fertilizer than once bloomers.  Fertilize with a low nitrogen fertilizer (5-10-5) mixed 50/50 with superphosphate 0-45-0). Dust fertilizer around and between the plants, careful to avoid direct application on the rhizome in spring and after spring bloom.  Apply a liquid foliar fertilizer one or two times in September.



Rebloomers also require a little more water than once bloomers.  Rebloomers need to be adequately watered once every other week if rain is insufficient.