Bearded iris 101
Over the years, my Niagara garden has played host to many different irises, only one or two have stayed the course, the others came, wowed me with their showy colours for a couple of years, and then began to fizzle out.
The irises became infected with a soft rot (iris borer?) that damaged the rhizomes. I tried digging them up, scraping out the rot and replanting the clean rhizomes, only to see the disease return the following year.
After a couple of years, I decided they were not worth the bother and tore most of them out. One iris, a charmer with variegated foliage and deliciously perfumed flowers (and self-sufficient habits) Iris pallida ‘Variegata’, has been with me from the beginning.
Enter a son who loves irises. He tends them lovingly in his clients’ gardens, brings spare divisions home and occasionally plants them in my garden, despite my objections. Of course, under his watchful eye, they thrive.
Old-time gardeners grew bearded irises in their home gardens, along with peonies, daylilies and lilacs. A person could bring home a division or two of any one of these plants and they would probably settle in to their new home without much of a fuss. Abandoned homesteads and historic graveyards often host heirloom plants that come back year after year without any attention.
Could it be that bearded irises unwittingly respond to love, or do they just thrive on neglect? With the irises in full bloom, let’s take a closer look at a few best practices for their culture and care.
Here in Niagara, bearded irises usually bloom in early June before the heat of the summer sets in. The best time to plant iris rhizomes is after they have bloomed and become dormant, during the months of July and August. The newly planted rhizomes need time to become established before the cool weather sets in — July and August are the ideal months for planting and/or transplanting. Potted iris should be planted at the same depth as they are growing in the pot, and can be planted at any time.
Irises love to bake in the sun — they need at least six to eight hours of direct sunlight each day — they will live (but rarely flower) if they do not receive enough sunlight. Irises also need well drained soil, adding humus or compost to heavy clay soil will help, but planting irises in a raised bed or on a slope is the best solution. Irises are very tolerant of less than ideal soils, but they cannot stand wet feet.
When planting bare iris rhizomes, build up the soil to form a little ridge. Place the rhizome on top of the ridge with the roots falling on either side of the ridge. Cover the rhizome and roots with soil, but keep the top of the rhizome visible (do not cover it with soil). Tamp the soil gently around the roots and water well. It is a common mistake to plant irises too deeply. Plant the rhizomes 30 to 45 centimetres apart, giving them a little extra ‘growing space’ so that they will not be overcrowded in a year or two, and need dividing. A little patience now will save you a lot of work later. Keep the new rhizomes watered (deep enough to penetrate the shallow root system) until the roots become established. Do not over water.
A light application of a well-balanced fertilizer with a ratio of 10-10-10 or 5-1010 in the early spring and again in the early summer after they have flowered, is recommended. Sprinkle the fertilizer around (never on) the rhizome.
After three to five years, the irises may become overcrowded and produce less flowers, this is a sign that they need to be divided. Established clumps may be thinned by removing several clumps and leaving the rest in the ground. A better practice is to dig up the entire clump, work the soil and add fresh compost, and then replant several of the largest, healthiest rhizomes. Spare rhizomes can be used to increase your stock, share with friends and family or pot them up for horticultural society plant sales.
Irises and weeds are not good bedfellows — it is important to keep the beds free of weeds and and fallen leaves so that the rhizomes can bask in the summer sun, never cover the rhizomes with mulch. Spacing the plants for good air circulation is also beneficial. Promptly remove spent flower stalks when possible.
Want to learn more about irises? Visit the Canadian Iris Society cdn-iris.ca or Chapman Iris (in Guelph) chapmaniris.com. The Laking Garden at Royal Botanical Gardens in Burlington reopened Friday and features a beautiful iris display at this time of the year.