Iris from C and T Iris Patch
Logo of C and T Iris Patch
 

Frequently Asked Questions

Iris Culture


Answers About Iris Culture

When do irises bloom?

Here in northern Colorado, tall bearded iris normally blooms May 25 through June 12 if the weather is average. The smaller iris classes bloom from around May 10 through June 1 - again depending on the weather.


Are certain varieties more fragrant than others?

Yes, most irises have some fragrance, however some have more than others.


Why are some varieties more expensive than others?

As a rule, the newer the variety the more expensive. A variety which came out in 2006 will be more expensive because they are not as available as varieties which became available in 1990.


Why do iris multiply?

The easiest way iris reproduce is like potatoes, they grow eyes which grow into mature rhizomes in one year. They can reproduce by seeds but that is usually not as successful.


Are there any weed killers compatible with iris?

Any chemical which kills weeds will kill irises. Pre-emergent herbicides that keep weeds from germinating are safe around irises.


Do iris need winter protection?

We recommend timely planting so new plants have time to establish good roots before hard winter weather sets in.


What do you use to mulch?

Avoid all mulches, ground cover, or manmade weed barriers to control weeds. If you cover iris with anything, your chance of soft rot increases greatly. Irises need to breathe.


Why aren't my iris blooming?

Iris need lots of sun, good drainage, and lots of good soil. Anything that puts stress on the plant can prevent blooming, such as iris clumps that are too large, lack of phosphate in the soil, and heat and drought stress. As a rule about 70% of first years´ planting blooms. Some varieties if iris are harder to get started because of breeding, just be patient.


Why are some of my rebloomers not reblooming?

Your rebloom success will depend on the fertility of your soil, local climate conditions, including the microclimates within your own garden. Some varieties take 2 or more years before they will rebloom. Some reblooming varieties will rebloom only occasionally no matter how well one takes care of them. Heat and drought stress can also delay reblooming until the weather cools off in fall similar to spring temperatures at the time of reblooming. Rainfall is also a plus.


What can I do to help my rebloomers bloom?

Make sure you have enough phosphate in your soil. You can apply a low nitrogen content fertilizer, (5-10-5), mixed with super phosphate, (0-45-0), applied mid-July. We use rabbit feed for the phosphate fertilizer which also has some micronutrients for the irises.

Do not let your rebloomers go dormant, water at least once a week if rainfall is not sufficient. Do not cut back foliage in summer on rebloomers, (as well as other types of iris unless transplanting), they may not rebloom as there is a substance produced by their leaves that stimulates reblooming stalk development.

Be aware of your climate zone. Reblooming irises that rebloom in warmer zones may not rebloom in cooler zones. Irises that rebloom in cooler zones will probably also rebloom going to warmer zones.


Why do iris change color?

If your iris are blooming a different color than originally purchased, it is because of letting your iris go to seed: the bloom stalk was not removed shortly after blooming. Bees do a wonderful job of pollinating different colors for the following year. The dominant color of iris is purple and will take over if the bloom stalk is not removed shortly after the bloom dries up. Chemical damage, overcrowding, and heat stress can be a factor in some color changes.


My iris have buds but don't bloom, the bud just turns brown and drops off?

Iris grow fast in spring before blooming. If you experience a late frost or an extremely cold night while the iris is budding, it aborts the new bud. Frost can also turn a blossom's color into white purplish streaks that are different than the color of the iris is supposed to be. Do not panic; just wait for new buds to form later on and the plant will be fine.


Why do leaves wrinkle up and look corrugated?

This is caused by unusual weather conditions such as becoming too hot too fast, drought and heat stress. Chemical damage can also wrinkle leaves, but heat is the main reason.


Why don't all irises grow the same?

Each variety is different. Some are more vigorous than others and increase rapidly, while others are slower and divide more slowly.


What is scorch?

Scorch is a brownish yellow color in the center leaf in the fan. Scorch occurs after a mild winter in colder climates. The result is stress on the plant that occurs when it starts to grow sooner than it should.


How do I care for iris once established?

Fertilize in early spring, and again in late July for rebloomers and newly divided plants. Water as needed but do not overwater. Keep your beds clean and free of weeds as much as possible and make sure to cut off bloom stalks soon after flowering.


When do I clean my iris beds?

Here in our dry climate in northern Colorado, major cleanup is in early spring. All dry and dead leaves are removed in early March, so only new growth is left.