Generally speaking, bearded irises will look after themselves over the winter, unless of course there’s jobs you didn’t get done in the autumn.
Irises can be divided in the autumn. If you didn’t get to them then, they can still be done now, but you may lessen the chances of a bloom this season. If dividing now, trim your leaves back by about two thirds for tall irises. Once split and replanted, the roots will die back and new roots will quickly form.
During the winter months you may notice some of the leaves dying back, going brown or developing some ‘rust’ spots. This is quite normal and it is not necessary to remove the spent leaves – the irises will discard them as they make new growth. The leaves can of course be gently removed and discarded if you want to do a general tidy-up. This may also reduce the spread of any fungal diseases. If you are particularly concerned about the rust spots, you can purchase a fungal spray which contains Mancozeb.
Michael Barnes, from the NSW Iris Society, has some great tips regarding fertilizing your irises. He suggests-
If you’re going to fertilize, remember it’s the months starting with A in which you do so. In August, I’ll be spreading a custom blend with an NPK of 13-14-12. …. Keep nitrogen levels down for your irises or you’ll end up with super foliage but less bloom spikes.
Happy gardening over the winter months – bring on spring and the blooms!