Growing Bearded Iris: When To Plant, Trim, Feed, Divide By Month

Summary: Bearded Iris put on a colorful show in the landscape. But to enjoy the show bearded Iris needs some attention during the year. Below you’ll find tips on when to trim, feed, plant, divide, and other more to make plants grow and bloom their best!

Colorful bearded Iris bloomPin

April

Clean up around the base of Iris clumps any leaves or sticks that may have blown in during the winter. Push back any plants that have been heaved out of the soil with the spring thaw. 

Double-check labels and make sure that they are firmly in place and legible. Iris borer activity begins this month. Spray or dust plants every ten days until blooming.

May

Feed Iris this month while plants are actively growing. 

Use a complete fertilizer, a cup per clump, and sprinkle between plants, not directly on the rhizomes. No more fertilizer is needed until late August or early September. 

Watering is beneficial, especially during periods of extreme drought. Iris will withstand a remarkable degree of dryness but will grow better when given supplemental waterings. 

Avoid splashing water, and do not pour water directly into the center of the clump. A slow saturating application between plants is the best procedure. Scratch up the soil a day or so after watering to prevent caking.

June

Blooming of the tall bearded Iris reaches a peak this month. Plan to visit public parks and the gardens of iris specialists. Make notes of unusual color combinations, blooming dates, and habits of growth. 

If your iris are grouped in a perennial border, consider the addition of good plant associates for foliage contrast such as thalictrum, baptisia, thermopsis, artemesia, astilbe, columbine, and peonies. 

Enjoy the thrill of growing at least a few Iris from seed you have produced. 

Start this month by pollinating some choice blooms. Iris enthusiasts are sponsoring shows this month. Plan to enter a few of your specimen blooms and enjoy those of others at the same time.

July

Planting is done this month. 

  • Select a location that receives full sun. 
  • Well-drained soil is of prime importance. 
  • Prepare carefully, two weeks before planting to allow settling, and incorporate a complete fertilizer such as 5-10-5. 
  • When planting, spread roots carefully and set so that the top of the rhizome is just covered with soil. 
  • Space 10″ inches apart in a triangular pattern with the growing points or “noses” facing in one direction. 
  • On older plants, remove all faded flowers and water beds if extremely dry. 

In northern climates, consider dividing and resetting plants after blooming rather than waiting until September. This allows a longer time for plants to become established.

August

Dividing old clumps should be done now (or immediately after blooming) when the plants are semi-dormant. 

If not divided every few years, there will be few blooms. 

  • Cut foliage to 6″ inches and dig out the clump. 
  • Wash soil from roots with a strong stream of water. 
  • The healthy young rhizomes are found on the outer edge of the clump. 
  • Make divisions by cutting away the old rhizomes with a sharp knife. 
  • Divide to either a single rhizome or to a “double.” 
  • There will usually be more bloom the first year from a “double” division. 
  • Soil should be carefully prepared and rhizomes planted as indicated for July.

September

Harvest seeds when pods are dry and begin to split. In the South, plant as soon as the seeds are harvested. In colder areas, plant in November or just before ground freezes. 

NOTE: Planting may be deferred until spring as fall germination sometimes occurs with subsequent injury.

Plant in a cold frame 1″ inch deep and 1″ inch apart in rows 6″ inches apart. Germination will commence (from November-planted seed) in late March in the New York area. 

By June, seedlings will be ready to transplant. Space 12″ inches apart in rows 18″ inches apart. 

Clean up old Iris plants by cutting them back to 6″ inches. Remove dead leaves and debris from the base of the clump on these that the eggs of borers are usually laid.