Not so long ago, every note on the cultivation of tall bearded irises insisted that three things were necessary to grow them successfully, and one thing should be avoided.
The three “essentials” of growing irises were a sunny position, sharp drainage, and lime. Are these golden rules true today? Only partially.
It is quite true that they should be planted in full sun, although some of the more delicately colored flowers may be prevented from fading by choosing a place where they will have protection from the sun’s rays for part of the day.
Good Drainage Is Necessary
Good drainage is also necessary, but there is no need to go to extremes when preparing iris beds except on the heaviest soils.
Provided dividing old iris clumps every three years for best results, drainage is normally good, as it is in nine out of ten gardens, no special steps need to be taken.
It should be sufficient on heavy loams if the beds are raised a few inches above the general level.
The natural drainage should be sharp enough to please irises in gardens on light to medium loams. Clay, of course, is quite another proposition, as all those luckless people who have to cope with it knows.
Raising iris beds in gardens on clay may not be enough, and in serious cases of waterlogging, it may be necessary to lay land drains.
Assuming that conditions do not necessitate this major operation, it will still be advisable to do all one can to lighten the soil by digging in ashes, strawy manure, compost, peat, or even straw.
Use of Lime
The old belief that lime is necessary to irises dies hard. It is, however, now generally considered that except on the most acid soils—the kind wrongly described as rhododendron soil, rhododendrons disliking extremely acid conditions—it is not only unnecessary to add lime, but it can be harmful, as it produces conditions conducive to rhizome rot.
If very acidic conditions prevail, the gentler forms of lime should be used, such as old mortar rubble, ground limestone, or, on light soils, powdered chalk.
Use Humus
Irises, like other plants, need humus, which must be provided to make good growth, fine foliage, and flowers.
They will “row passably and make a fair show if simply stuck in the ground that has received no prior treatment, but if we want them to do their best, we must assist them.
To add humus, we may, besides digging in manure, or as well as doing so, dig in spent hops, leaf mold, or compost.
Three Top Dressings of Superphosphate
Three top dressings of superphosphate per year are often advised, the first in spring when growth is active, one in June after the flowers have faded, and one in late August or early September.
Many growers vary the dressings, using combined fertilizers (containing phosphates, nitrogen, and potash), poultry manure, dried blood, fish manure (all nitrogenous), and bone meal.
Except, however, on the hungriest soils, I think two dressings annually are quite sufficient, one in spring, the other in early autumn, as at both these times irises will be growing strongly.
Stock Dressing
The ‘stock’ dressing is superphosphate, and this is useful on calcareous soils as it helps to counteract alkalinity.
On slightly acid soils, I would prefer to use a balanced fertilizer in spring sprinkled between, not on, the plants, and for the autumnal dressing to add to the fertilizer either rotted poultry or barnyard manure (the commercial products are safe).
Top dressings are all very well, but they do not make up for any skimping in the original preparation of the soil.
Unless rain falls, all top dressings should be well watered in, following up with the hoe as soon as the surface soil is dry enough. Hoe shallowly to avoid damaging the roots, which will be near the surface.
Planted Iris Needs Care
Once an iris is planted, it needs little care, but there are one or two small things an iris lover will attend to.
Dead flowers should be removed promptly, not only for the sake of neatness and beauty but because the pulpy dead petals, particularly in a wet season, may cling to and spoil later flowers.
Flower stems should be removed after the display is over, either by snapping them off at the base by bending them over sharply or by cutting them off flush with the rhizome.
The disadvantage of the first method is that some stems are tough, the force one has to use may lift the rhizome, and then the snapping off often results in the stem coming away with a chunk of rhizome attached.
I prefer to cut them down, taking care to leave no stump, as rot may begin there and travel down into the rhizome.
Dead and dying leaves should be removed at least twice a year, in late autumn and early spring. They should be pulled away gently, not snatched, and should be burnt, as they may contain spores of disease.
Some growers cut the leaves down to about 9 inches in autumn, and this practice certainly leads to neatness as well as helps cleanliness by removing disease spores.
44659 by N. Leslie Cave