Iris root rot – Success with Iris begins with good hygiene

Photo Credit: Photobucket Healthy Iris roots
Like a mantra in my mind, I still recall my late grandmother words “Cleanliness is next to Godliness” and whilst thanks to my gran, personal hygiene has never been a problem for me! Many of us seem to struggle with keeping our Gardens soil sanitised and therefore free from soul destroying pests and diseases that can annihilate a favoured flowering crop or harvest. 

In a world where we all want the latest, newest, strongest garden plants and flowers, adding interesting cultivars to our growing collection of plants is as common place as shopping for groceries.

Our favoured garden centre, online marketplace or friends garden can often be a rich source of new plant material, often greatly appreciated and planted into our own garden soil with little consideration to the problems we may be inviting for the future.

Iris Root Rot

Garden pests and disease often lay dormant and hidden from sight during much of the year waiting for the perfect conditions to begin to devour our cherished roots, leaves and flowers of our garden flora. Introducing new plants, roots and bulbs should be addressed with some caution and whilst building and sharing your plant collection with others is widely encouraged you are going to want to be sure you are both giving and receiving healthy plant material.

Photo credit: Photobucket
Iris rhizome is typical for suffering from damage from a nocturnal brown moth that lays its larvae near your Iris. These caterpillar larvae are responsible for boring into your Iris roots leaving small pin pick holes where the roots used to anchor the rhizome to your garden soil. Feeding on the tasty starch filled iris roots the larvae quickly devours much of the storage mechanism that supports future growth and ultimately flowers from your chosen Iris variety.

Iris Root Rot

Left unchecked Iris borer will turn your Iris bed into a rotting, smelly mess of decomposing rhizomes that will never recover and may even affect nearby tubers and bulbs, so it is really important that when maintaining your Iris beds and borders that you learn to identify the telltale signs of iris root rot and how to minimize it’s spread.

Remove the old flowering stem from the rhizome to help prevent rot.
Remove the old flowering stem from the rhizome to help prevent rot.

Perhaps you have enjoyed Iris flowers for the last few years in your garden and suddenly you are away from a decline in flowers, of course simply overcrowding may the cause, but if on investigation your Iris leaves are also showing signs of wilt or decay then further investigation is necessary.

Firstly examine around the base of several rhizomes and check to see if they are firm and still well anchored to the soil! If however they show signs of rot or even look to be shrinking in size? Then a further investigation is required and time to get out a digging spade, trowel, fork and a sharp clean knife and some Jeyes Fluid wet wipes.

Sanitation is critical at this stage and your tools must be kept free from contamination a simple bleach and water solution in a clean bucket will allow you to rinse off your garden implements before re-using in another area of the garden. Digging around the base of the infected rhizomes you will notice that the roots have failed and shrivelled away, often leaving behind a withered or soggy root that is in a stage of decay.

Removing the infected rhizomes is an essential part of housekeeping as these will not regrow and only lead to further problems.  Iris borer may be the initial cause of the problem brought on by the moth that lays the eggs in the garden soil ready to hatch caterpillar larvae that will hungrily feed up the Iris roots but once they have had their feed a bacteria rot will set in to turn your once healthy firm rhizomes to mush.

A sharp garden knife can be used to cut away the decaying part of the infected Iris root, make a clean cut into firm root and dust with a fungicide, leaving the exposed rhizome to dry and heal in the heat of the sun for a few days before replanting. This process of diving Iris roots is a traditional method of increasing flowering stems and improving the health of your plants but it is imperative that you remove all decaying matter to prevent re-infection.

Small garden tools can be cleaned and sterilised quickly with sanitised wipes often used in the bathroom or kitchen, larger garden implements should be thoroughly cleaned using bleach or Jeyes fluid and the washings disposed of in an ecological sound manner.

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Stephen Pryce-Lea

Head Gardener and International Horticultural Consulatant




“It’s a beautiful thing when a career and a passion grow together, when you find it in a Garden it’s like finding Paradise“

iGrowHort – A Head Gardener’s Horticultural Journey of love, life and learning.



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