A beginner's guide to growing irises

From the stately bearded iris — long known as the flag iris — down to the tiny plants that grow from bulbs, these flowers provide a delicate beauty in any garden.  Follow these guidelines to learn how to properly grow irises so they flourish.

There are two groups: those that grow from rhizomes (thick underground stems) and those that grow from bulbs.

• The rhizomatous types develop pointed, straplike leaves that grow in fans from the ends of the rhizomes and produce stalks that bear one or more flowers. Colours include white, pink, blue, purple-black, gold, and red, as well as many combinations of these hues.
• The most popular of these types are the bearded irises, which have fleshy hairs like a beard on the outer petals, or "falls."
• In addition to the bearded irises, there are the equally beautiful Eurasian beardless (Spathula) types.

Most rhizomatous irises can be planted in the same manner, and all share the need for proper soil preparation if plants are to bloom and multiply through the years. Good drainage is essential, and full sun is generally best, although a few varieties prefer a little shade.

Almost any soil is suitable for irises, but heavy clay and light sand demand more preparation than loam and clay loam, which are the best mediums for these perennials.

Heavy clay soils can be encouraged to drain better if generous amounts of sharp sand, humus, and peat moss are added. Conversely, very sandy soils will retain moisture longer if humus and peat moss are mixed in.

• Bearded iris rhizomes should be planted between midsummer and early fall. Where midsummers are extremely dry and hot, early-fall planting can help reduce stress on the plants. Inspect the rhizomes carefully for evidence of damage by borers or rot.
• With a sharp knife, cut away decayed parts and broken roots.
• Dust all cut surfaces with sulphur, or you could soak the rhizomes for half an hour in streptomycin to discourage recurring disease.
• For best effect, plant three to seven rhizomes of the same variety in a clump.
• Plant them with the roots down either side of a ridge of soil so that the top of the rhizome is just showing.
• Face the fans away from the centre of the clump.
• Press the soil firmly around the rhizomes to drive out air pockets, which cause soil to dry out and also impede anchoring.
• Label clumps.

Before planting beardless irises, take the same precautions regarding borers and rot as you would with bearded types.

• Begin planting in early fall, except with Pacific Coast irises. These respond better to mid-spring planting, which takes less energy from the rhizomes. Spurias should be planted in mid to late fall, since early-fall weather is often too dry.
• Rhizomes of most varieties should be planted 38 to 45 centimetres (14 to 18 inches) apart and about five centimetres (two inches) deep.
• Water new plantings well, and keep them moist until rhizomes are well established.
• Apply a mulch to conserve moisture and diminish the unavoidable shock of transplanting. This is especially important with crested irises, which are planted close to the soil surface and are vulnerable to drying out.