When to Cut Back Irises

A popular ornamental spring flower, did you know that there are over 300 different types of iris? These different varieties come in a range of different shapes and colors, from large border filling specimens to smaller container plants.

Part of the Iridaceae plant family the iris is not only visually attractive it is also easy to grow and care for. One of the most important aspects of caring for these attractive plants is knowing when to cut back irises. This helps to keep the plants healthy and promotes regular flowering displays.

If you are unsure, or have never done this before, our guide to when to cut back irises is designed to explain how and when to prune your plants to guarantee large, colorful floral displays year after year.

Knowing when to cut back irises helps to keep the plants healthy and productive.  

Why You Should Learn When to Cut Back Irises

Learning how and when to cut back irises benefits your plants in a number of different ways.

Firstly, knowing when to cut back irises can help the plants to maximize the amount of energy stored in their bulb or rhizome. This energy is vital for flowering the following year.

Correctly knowing how and when to cut back irises also helps to protect the plants from fungal and bacterial diseases such as powdery mildew. This unsightly disease is most common on overcrowded plants with moist or wet foliage.

Iris foliage is prone to both fungal and bacterial disease. 

Iris plants are also vulnerable to developing blight, soft rot and leaf spot. Many of these issues can cause brown spots to form on leaves or for foliage to become discolored. If allowed to develop, some diseases can cause the rhizomes to turn to mush.

Keeping the plants neat and tidy helps to prevent most of these issues. Pruning also helps to improve air circulation around the plants; this, in turn, again helps to prevent fungal issues from developing.

If your plants show any signs of disease, cut back irises and discard the affected foliage. Do not place it on a compost heap.

Cut away the foliage as close to the base of the plant as possible. Remember to clean and sterilize your tools after use.

Allowing the foliage to overwinter on the plant also provides hiding places for potentially harmful insects.

The Macronoctua Onusta or brown moth likes to lay its eggs on dead foliage for overwintering. In the spring, usually April or May, the larvae of the iris borer hatches.

These destructive pests eat the leaves of your irises, causing them to become yellow or slimy, before boring down into the plant’s rhizome. This can cause root rot to develop. Affected plants can also emit an unpleasant, putrid smell.

Knowing when to cut back irises, as well as how to do it correctly, helps to keep your plants healthy and problem free.

Learning when to cut back irises is pleasingly easy and rewarding.  

When to Cut Back Irises After Flowering

Deadheading is an important part of garden maintenance. When it comes to caring for irises, pruning and removing the spent flower stalks helps to keep the plant’s sword-like leaves healthy and productive.

Most varieties of iris send up a flower stalk which produces several flowers incrementally over the course of a few weeks. Unlike some flowers, deadheading a spent bloom will not encourage a new flower to develop. Instead, allow all the flowers to form on the stem before cutting away the entire stalk once flowering has finished.

There is no need to deadhead each individual flower as it fades.

Not only are stalks without flowers or wilted blooms unattractive, they can also take away energy and nutrients from the plant. Allowing spent flower stalks to remain on the plant can cause the iris to waste energy on seed head production.

The energy wasted in the seed production process could otherwise be stored in the bulb or rhizome and used to power foliage and flower production next year. The more energy stored in the rhizome, the better the foliage and floral display the following year.

Some varieties of iris such as the Bearded iris produce a second floral display in mid to late summer or early fall. Once the flowering cycle is complete for the year, use sterile hand pruners or clippers to cut back the spent flower stalks. Again, cut as close to the base as possible.

Allowing seed heads to form is a waste of energy.

When pruning, try to make angled cuts. This encourages water to run off the stalks preventing mildew and rot from developing.

When to Cut Back Diseased Irises

Regularly check your flowers for signs of disease or infestation. Should any parts of the plant’s foliage look unhealthy, use sharp pruners to cut back the leaves. Make your cuts as close to the base of the plant as possible.

The sword-like foliage should be green and healthy.

Only cut back the diseased or damaged leaves. Healthy leaves can be left in place.

Do not place diseased leaves on the compost pile. This can infect the compost and, if used on your garden, cause more harm than good.

After pruning, clean your tools. Again this prevents the accidental transfer of disease around the garden.

When to Cut Back Irises in Late Summer or Fall

The best time to cut back irises is in mid fall when flowering has finished for the year but before the frosts and cooler temperatures of winter arrive. At this stage of the year you can ‘fan trim’ the plants.

The leaves of the iris can continue to photosynthesize as long as the temperature remains over freezing. However, allowing the large leaves to remain in place well into winter can make your garden look untidy. It can also make the plant more susceptible to disease or infestation.

Fan trimming enables your plants to continue to photosynthesize and store energy in their rhizome or bulb whilst also keeping your garden looking neat and tidy. It also helps to maintain annual, consistent flowering.

To ‘fan trim’ you will need sterile scissors, trimmers or hand shears. Start in the middle of the foliage clump, cutting downwards at an angle along each leaf.

Cut back the center leaves to a height of 4 to 5 inches. The lower leaves can be cut back to a height of 2 to 3 inches. This creates an attractive fan shape which helps to keep the leaves healthy and allows photosynthesis to continue. It also prevents moisture from accumulating at the center of the clump.

Any dried, discolored or diseased leaves can be completely cut back. Dry or discolored leaves can be placed on the compost pile. Diseased leaves should be disposed of.

https://www.youtube.com/watch?v=L4PyRxrdfso 

When to Cut Back Irises After Frost

Once the cold weather has arrived and the first true frosts of winter have formed, the iris foliage naturally dies back. When this happens you can cut back irises more severely. Use sterile hand pruners or small shearers to cut away the dead foliage. Cut roughly half an inch to an inch above the rhizome or soil level.

Cut the foliage back after the first frosts of fall or winter.

Remember to make angled cuts. This encourages rainwater to drain away. If rain water is allowed to settle on the plant, rot can develop.

Do not pull up the dead or dying leaves. This can damage the rhizome, creating an entry point for pests or disease.

After you cut back irises for the year, it is a good time to check the health of the rhizome. To do this, run your hands over the surface of the rhizome and surrounding soil. If your iris is mature, or has a good sized clump, you should be able to feel rhizomes close to the soil surface.

Soft rhizomes are probably damaged or unlikely to develop into flowering specimens. These can be cut away from the rhizome with clean, sharp scissors. Discard the soft rhizomes by placing them on the compost heap.

When to Cut Back Irises for Propagation

The iris is most easily propagated by dividing the rhizome. The rhizome is a horizontal, underground stem that is covered with nodes. These produce flower and foliage shoots as well as roots.

As well as being an easy way to get lots of new plants, division also helps to rejuvenate older plants and prevents overcrowding. This, in turn, keeps your garden healthy and productive.

Do not attempt to divide or propagate young plants. Give your irises time to mature, dividing for the first time when they are 2 to 3 years old. After this you can divide the plants every 3 to 5 years depending on how quickly they are growing. In fertile soils you may need to divide your iris plants every 2 to 3 years.

Unlike some plants that are best divided in the winter, you should never divide iris plants during cold weather.

You should also avoid dividing rhizomes in late winter or early spring, when the plant is preparing to resume growing. Dividing now can deter growth and flowering.

Divisions are best made in the late summer or fall. Ideally you should divide the plants no later than 6 to 8 weeks after flowering has finished for the year.

To divide, use a large garden fork to carefully dig up the iris clumps. Place on a dry surface, such as a potting bench and examine the clump, deciding where to make your divisions. At this stage you can also remove any trimmed flowers that are still present.

Each division must have a thick, healthy rhizome and multiple roots. Ripe, viable rhizomes usually separate easily from the larger clump. Use your fingers to pull apart any iris rhizomes that are stuck together.

After dividing the rhizomes, brush away or rinse off any dirt to check for signs of root rot or infestation. Diseased or damaged rhizomes should be discarded. Do not place them on the compost heap.

Healthy rhizomes can be replanted in good, well-draining soil roughly 1 inch deep. Be careful not to plant the rhizomes too deeply, this can deter flowering or slow growth. After planting, cover the rhizome and water so that the top 3 inches of soil feel damp.

Dividing and thinning out rhizomes helps to keep the plants healthy and productive.  

Iris Care Tips

Easy to care for, the iris is part of the Iridaceae plant family. While most varieties grow from rhizomes, some grow from bulbs. In the right conditions and with the right care, in particular knowing when to cut back irises, these are dependable perennial plants that can be relied upon to fill your garden with spring flowers.

In addition to knowing when to cut back irises, there are some other important care tips that you should keep in mind.

Firstly, plant your selected variety of iris in a sunny spot. The majority of cultivars favor full sun, but some do just as well in partial sun positions.

The soil should be rich and well draining. There are a number of ways to improve heavy, clay soil such as working in horticultural sand or compost before planting. This helps to lighten the soil, improving drainage. Alternatively, you can successfully grow your irises in raised beds or planters.

Iris plants thrive in well draining, rich soil. However there are some subtle differences between the different cultivars. For example, Louisiana and Japanese cultivars tolerate moist soil. Both cultivars are good choices for planting close to ponds. The Siberian iris does best in a moist, acidic soil.

Many types of iris do well close to water.

Depending on the variety your iris can achieve a maximum height of anywhere between 6 inches and 4 ft. Taller varieties, particularly those growing in exposed areas, may require some support to help them stay upright. Loosely tie the plants to a Hydrofarm Natural Bamboo Plant Stake.

Most varieties of iris are hardy in USDA Zones 3 to 9. In cooler climates you can grow the plants in pots, moving them inside during the colder, winter months. Plants growing in the ground can also be protected by covering the soil with a horticultural fleece, such as an Agfabric Frost Blanket, until your last frost date of the spring has passed.

Water your plants regularly and deeply. Try not to oversaturate the soil when watering. This can cause the rhizome to develop root rot. A soil moisture sensor provides a useful way to monitor the moisture content of your soil, helping to prevent rot and over-saturation.

Once established most varieties are drought-resistant. This means that they can tolerate being deprived of water for short spells. Some varieties, such as the Blue Flag iris, require a lot of water.

Instead of watering overhead, aim to water the soil around the plant or implement a HIRALIY Drip Irrigation System. Wet foliage is more prone to developing fungal disease.

The colorful iris requires regular watering. 

In the spring, loosen the soil around your plants and apply a healthy layer of compost. This gives the plants a nutrient boost which promotes growth and flowering. If you don’t have any compost you can apply a balanced flower fertilizer such as Miracle-Gro Water Soluble All Purpose Plant Food.

If you are using a fertilizer product be careful not to apply fertilizers that are too rich in nitrogen. This can lead to rot.

Iris varieties that flower twice during the spring and early summer may appreciate a second dose of fertilizer. This is best applied once the first flowers have faded and before the second round of flowers set.

Companion Planting

A spring flowering plant, plating your colorful irises alongside other spring flowering specimens adds color and interest to the garden. Reliable spring flowering bulbs include daffodils and tulips.

To prolong the life of your flower beds, plant summer flowering plants such as delphiniums, foxgloves and peonies alongside your spring flowering bulbs. These bloom as your irises fade.

Some of the best iris companion plants are:

• Monkshood,
• Allium,
• Pansy,
• Phlox
• Violet,
• Yarrow,
• Daisy,
• Black Eyed Susan,
• Cranesbill,
• Sedum,
• Hyssop.

The iris is a reliable addition to the flower garden.

Knowing when to cut back irises not only helps to keep these plants healthy and productive, it also helps to keep your garden looking good. Your irises will reward your taking the time to learn this important skill by producing rich, colorful floral displays year after year.

Additionally, this is a transferable skill. Once you know how and when to cut back irises you will have the confidence and knowledge to be able to prune other plants, helping to keep your garden pristine and productive.