What to Do With Irises in October – 6 Tips to Get Them Winter-Ready and Ensure Gorgeous Spring Flowers
Not all irises need the same fall care. Knowing what to cut back, what to leave alone, and how to protect their roots makes all the difference.
In most gardens, October is a pivotal transition period for perennials as they go from active growing and flowering to winter dormancy. As early-season bloomers, irises can look pretty tired by fall, but that doesn’t mean they don’t need care.
October iris care is all about preparing plants for dormancy and ensuring they’ll emerge healthy and flowering next spring. From preventing rot to managing pests and diseases, good care now ensures healthier growth next year.
Here, we’ll focus on October chores for bearded irises, the most commonly grown type, with notes on how care differs for Siberian and Japanese irises. Essential fall care includes trimming foliage, cleaning up around plants, dividing as needed, and managing mulch appropriately by iris type.
1. Trim Back Declining Foliage
Depending on where you live and garden, some or all of your iris foliage will be giving up the game by now. Much of the foliage will be yellow or dying. Use clean, sharp shears to remove spent leaves. For precise trimming around healthy foliage, try the Fiskars Titanium Micro-Tip Pruning Shears, available at Home Depot. Their narrow blades make it easier to snip away dying leaves without damaging neighboring growth.
In general, trim established plants back to about six to eight inches (15 to 20 cm). Leaving leaves intact can cause winter damage that collapses onto the rhizomes, increasing the risk of rot.
Leave any healthy green leaves intact, as they are still photosynthesizing and gathering energy for the plant to use next year. In milder climates, you might still see a lot of green leaves, so you’ll need to delay trimming until the plant has more yellowing leaves.
2. Clear out Garden Debris
It’s very important to remove debris from around and under your irises before winter. Remove all fallen and dead leaves, stems, weeds, and other plant material and compost it, or, if diseased, dispose of it in the garbage.
This chore is crucial because leftover material can increase the risk of plants getting diseases or being infested with pests later. The iris borer lays eggs in dead foliage, which overwinter there and hatch in the spring. Removing debris also opens up airflow, reducing the risk of fungal infections.
If iris borers have been a problem in your garden, make a note to tackle them again in spring. A spinosad-based insecticide, such as Bonide Captain Jack's Deadbug Brew, available on Amazon, can help control newly hatched larvae before they burrow into the plants. Apply when new iris shoots reach around 4–6 inches tall (10–15 cm).
3. Check Rhizomes for Rot
Bearded irises store energy in fleshy rhizomes near the soil surface. They may rot if moisture levels are too high. It’s a good idea to check for and manage any areas of rot on rhizomes now, so they don’t get worse over winter. Brush back the soil from the tops of the rhizomes and inspect them for spots that look soft, mushy, or dark, or that have a bad smell.
Use a sharp, clean garden knife to cut out rotten areas until you reach healthy, firm rhizome tissue. A tool such as the Fiskars Big Grip Garden Knife, available at Amazon, is also handy for carefully lifting affected rhizomes to inspect them more closely. Disinfect the blade between cuts to avoid spreading infection. If a rhizome is severely rotted, it’s usually best to remove and discard it.
If you find a lot of rot, check drainage around the plants and make sure water isn’t pooling. Japanese and Siberian irises also grow from rhizomes, but these are generally less exposed than those of bearded irises. You can still check around the crowns for signs of rot or damage caused by excessive moisture.
4. Divide and Replant Irises
Fall is generally a good time to divide bearded irises. However, October might be too late in some areas. In milder climates (zones 7 to 9), you can divide irises now. In colder areas, October is likely too late to move irises and expect them to establish before winter.
If you are dividing an iris now, lift the clumps carefully. A sturdy digging tool, such as the Radius Garden Root Slayer Shovel, available at Home Depot, has a serrated blade that makes it easier to dig around dense, established clumps. Take care not to damage the rhizomes as you lift them. Separate the rhizomes, ensuring each one has a healthy fan of leaves. Plant the divisions in suitable areas right away, making sure they have good drainage and that the rhizomes remain near the surface. Siberian and Japanese irises are best divided in spring.
If it’s too late to make divisions now, you can still plan ahead by identifying large clumps that could benefit from a spring division. Target bearded iris clumps that are spreading into dense patches, have a bare center, or have not produced as many flowers as in previous years.
Label or photograph the clumps you plan to target in spring, so you don’t forget. It’s not always easy to identify the overgrown irises in spring. The best time to divide next year is after flowering.
A little fall care goes a long way toward establishing healthy, flowering irises in spring. It’s easy to forget these early bloomers come fall, but don’t make the mistake of ignoring them. Irises need fall care to ease their way into winter in good health.
5. Avoid Mulching, or Mulch Lightly
Bearded irises are different from many perennials in that they generally should not be mulched over in winter. The rhizomes need to remain near the soil surface and slightly exposed to air and sunlight to stay dry and avoid rotting. Never cover them in heavy layers of mulch or compost.
If you have very cold winters, you can apply a thin layer of more breathable mulch to prevent frost heaving. Use pine needles or clean straw, like CleanStraw Longleaf Pine Straw Mulch from Walmart. Other types of irises can benefit from a more typical layer of mulch to retain moisture and as protection against cold.
6. Stop Feeding and Adjust Watering
Growth is slowing and stopping this time of year as irises prepare for winter dormancy. This means they no longer need fertilizer. Stop feeding irises now to avoid promoting fresh new growth that will only expend energy and freeze in winter.
You can also slow down your watering routine as temperatures drop, especially if your area is getting more rain. Rather than following a fixed schedule, check the soil every few days for moisture and water as needed. A Yamron 4-in-1 Soil Moisture Meter, available at Amazon, can help you monitor moisture levels and avoid overwatering. Newly transplanted divisions will need more consistent moisture as they establish roots, but take care not to leave the soil waterlogged.
Iris Care Essentials
