When To Cut Back Iris?

The best time to prune iris plants is in the autumn. After the plants have finished blooming in the spring, the spent flower stalks can be removed, but the foliage should remain in place throughout the summer. The leaves should be cut back to about 3 inches above the soil line in mid-autumn. The next step is removing the trimmed foliage, autumn leaves, and other debris from the rhizomes. Overwintering pests will no longer have a place to hide out (and make spring cleanup easier). It’s also the best time to introduce new iris varieties to the landscape (especially the new reblooming types).

The majority of gardeners have a daily or weekly task of deadheading their plants. When the spent flowers of some plants are removed, this encourages the growth of new blooms in their stead. However, bearded irises are an exception. It’s not uncommon for many varieties to bloom just once in the late spring. Irises, like peonies, will not bloom again until the following year, even if you deadhead them. However, there are only a few varieties of bearded irises that rebloom in autumn. Despite this, trimming spent iris flower stalks is still recommended to maintain a tidy appearance and guard against diseases such as botrytis. After all the blooms have faded, it’s time to remove the flower stalks.

Blue and Yellow Siberian Iris.

Why Is It Important To Know When To Prune Your Irises?

During the first 2-3 weeks of spring, bearded irises put on quite a show, but the plants become much less attractive once their blooms fade. For a beautiful landscape, you’ll need to remove the dead flowers. It is also important to consider disease prevention when deciding when to remove the spent flower stalks. Proper iris care can reduce or eliminate several common iris diseases, including iris pruning. Iris borer pests can be prevented by cutting back the plants when they’re at their peak.

When Do You Cut Back the Iris Flower Stalks?

Most gardeners have to deadhead their plants every day or every week. Removing the spent flowers from some types of plants encourages the growth of new flowers. There are, however, bearded irises that don’t work like this. Most types of flowers only bloom once in the late spring, which is for the year. Like peonies, even if you kill off irises, they won’t bloom again until the next year, even if you cut them off now and then. Bearded Iris blooms again in the fall, but they are not very common. If you want to keep your plants looking good and avoid diseases like botrytis, you should still cut off the flower stalks of your irises when they’re done blooming. Right now is a good time to cut down the flower stalks. A few days after the blooms have faded, cut them down.

Deadheading Iris

  • When flowers die, they don’t need to be taken out one by one as they die. Instead, cut off the whole flower stalk at the end of the blooming season.
  • Using scissors, cut off the spent flower stalks from bearded iris plants. You should follow them down to the base of the plant, where they meet the rhizome (the thick fleshy root-like structure) and cut them off there.
  • When cutting the stem, cut it at an angle if you have to. Rain and irrigation water can get on it if you cut it flat. This can cause crown rot. Angled cuts help water run off the side.
Photo showing some blue iris flowers that are growing in a spring garden border, flowering in the sunshine. Their pointed green leaves are visible in the foreground and blurred in the background.

When Should Irises Be Trimmed Back To Keep Iris Borer at Bay?

This species of moth larva feeds on the bearded iris’s rhizomes. Iris foliage becomes slimy and yellow as a result of their feeding. Often, the plant emits a noxious odor (think rotten potato). Late summer is the time of year when female moths lay eggs on irises—these eggs hatch from the foliage that they’ve sat on all winter in the spring. As soon as a new foliage emerges, the caterpillars burrow into it. Begin feeding on within, working their way to the rhizome. A single borer can demolish an entire rhizome by mid-summer, leaving behind a stinky, smelly mess.

The larvae of the Iris borer are pinkish-white and chubby. Iris borers are common when dividing irises in the late summer. Borers pupate underground in August. Adult moths emerge a few weeks later to reproduce and lay more eggs.

Iris borers can be controlled with beneficial nematodes, but you can easily prevent further infestations if you know when to cut back your irises. Irises need to be cut back in the fall because the eggs will survive the winter on the foliage. Trim the leaves back to the rhizomes and discard or bury the resulting debris. Dig up and discard any soft, rotten rhizomes you come across.

When Should Irises Be Trimmed Back To Control Disease?

There are a number of diseases that bearded irises are prone to. Botrytis, ink spot, soft rot, and leaf spot are some of the more common bacterial leaf blight and botrytis diseases. Iris foliage is disfigured by brown spots or streaks caused by these diseases. Some turn the rhizomes into mush. Plants look dreadful because of the pesticides that are sprayed on them. A gardener is caught in a pickle.

Wet weather or damp, humid conditions encourage all of these diseases, so promoting good air circulation is essential to preventing or lessening their damage. If possible, avoid watering irises in the evening and instead make use of drip irrigation or a soaker hose. The longer the foliage is exposed to the elements, the better. You can’t control Mother Nature, so you’ll have to deal with some wet foliage at some point.

Keep an eye out for diseased iris leaves, and remove them as soon as they appear (spots, streaks, or blotches). The rhizome should be as short as possible. Remove any discolored foliage that appears as soon as possible. To keep the plants looking their best, I repeat this process two or three times during June and July.

Beautiful blue irises, “Ships Are Sailing” variety. For more of my flowers (CLICK HERE)

Keeping Irises Disease-Free by Pruning

If your plants are wilting and untidy by the end of the summer, you may want to consider removing the entire plant. Cut each “fan” of leaves in half with a pair of garden scissors. As a result, the rhizomes’ air circulation is improved, and rot is less likely to occur. It is best to cut each leaf blade at an angle to avoid rainwater pooling on the cut surface, leading to decay.

Completely remove all of the foliage at the end of the growing season after a few touches of frost. Leaf debris is the primary habitat for most iris diseases. Overwintering fungal spores are reduced by removing the foliage.