Buying plants packed in plastic is a waste of money, writes Lesley Cox, of the Otago Iris Group, as they inevitably rot and die.
Although there are species to bloom in just about every month of the year, spring and early summer — from September through Christmas — sees a great burgeoning of the colourful genus Iris, named for the Greek Goddess of the Rainbow. There is truly an explosion of shapes, sizes and every colour and shade imaginable, from white through black and everything in between. The greatest selection is within the Tall Bearded (TB) forms, which are at their height in October and November here in the South.
For this reason, I was shocked recently to see in a few local garden centres, the rhizomes of TBs packed in plastic bags, sweating and beginning to rot. Iris rhizomes, the in-ground storage organ of the plant, should never be sold at this time of year and they should never be sold or packed in plastic or any material in which they may become damp. Rhizomes should be in the ground, in full growth of deeply delving roots and vigorous fans of green foliage carrying the stems of gorgeous flowers.
All bearded irises of whatever kind should be planted after they have flowered and the foliage has matured. For TBs, this is generally from January through April during which time they are lifted, divided, trimmed and tidied (never be afraid to root-prune, leaving about 5cm of root to act as an anchor when replanting) then replanted in a good soil which has some well-rotted plant-based compost (not too much), and a good addition of lime. Dress with a general fertilizer at planting time then in autumn with a low nitrogen, high potassium fertilizer such as sulphate of potash, or tomato fertilizer, to encourage a good blooming. My experience tells me that the fertilizers given this year will bear best results not this coming spring but the following, i.e. 18-20 months after application, so if applied each year there should be good results even if the first year is a bit sparse.
Here in the South where soils tend to be quite heavy and we usually have higher rainfall, rhizomes should be positioned at or near the soil surface (hence the need to retain some of the old roots when cleaning) where the sun can ripen them and lead into a good flowering later. I also dig in a quantity of horticultural sand when planting bearded irises, to help with drainage and to encourage new, feeding roots.
The alternative is to buy quality rhizomes from a specialist nursery at this same, post-flowering time and there are several in New Zealand which will supply tall, medium (median) or miniature forms in great variety. Most issue a yearly mail order catalogue and the Otago Iris Group will happily supply a list of sources to anyone interested. These nurseries will pack your order in clean, dry newspaper, each iris separately and named. Please don’t buy plastic-packed plants in the spring, or at any time. You would be wasting your money and doomed to disappointment as they inevitably rot and die.
