How to Grow Irises

How to Grow Irises

You may have thought bearded Iris were only blue or purple. Or perhaps you may have thought they were difficult to grow. Today’s hybrid bearded Iris come in a rainbow of colors, and they’re one of the easiest perennials to grow.

With a minimum of care they will reward you with beautiful blooms year after year. Here are a few suggestions for growing Iris. Proper care is simple and quite easy. Treat your garden and yourself to some of these fine irises flowers.

When to Plant

For best results in Canada, Iris should be planted in mid-July or August. It’s important that the roots of newly planted Iris be well-established before the growing season ends. In areas with an early onset of winter early planting may be preferred (mid-July). Some of the more moderate areas may plant later (mid to late August).

Where to Plant

Iris need at least a half day of sun. In extremely hot climates some shade is beneficial, but in most climates Iris do best in full sun. Be sure to provide your Iris with good drainage, planting either on a slope or in raised beds.

Soil Preparation

Iris will thrive in most well-drained garden soils. Planting on a slope or in a raised bed helps ensure good drainage. If your soil is heavy, add coarse sand or humus to improve drainage. Gypsum is an excellent soil conditioner that can improve most clay soils.

The ideal soil pH is 6.8 (slightly acid), but Iris are tolerant in this regard. To adjust the pH of your soil, lime may be added to acidic soils or sulfur to alkaline soils. It is always best to have your soil analyzed before taking corrective measures.

Irises Planting

Irises Planting

Iris should be planted so the tops of the rhizomes are exposed and the roots are spread out, facing downward in the soil. In very light soils or in extremely hot climates, covering the rhizome with one inch of soil may be desirable. Firm the soil around each rhizome and then water to help settle the soil. A common mistake is to plant iris too deeply.

Distance Apart: Iris are generally planted 12 to 24 inches apart. Close planting gives an immediate effect but closely planted iris will need to be thinned often. Plants spaced further apart will need less frequent thinning.

Watering: Newly set plants need moisture to help their root systems become established. Specific watering information depends on your climate and your soil type, but keep in mind that deep watering at long intervals is better than more frequent shallow waterings. Once established, Iris normally don’t need to be watered except in arid areas. Over watering is a common error.

Fertilization: Specific fertilizer recommendations depend on your soil type but bone meal, superphosphate and 6-10-10 are all effective. A light application about a month after bloom will reward you with good growth and bloom. Avoid using anything high in nitrogen, as nitrogen encourages rot problems.

Thinning Old Clumps: Iris need to be thinned or divided before they become overcrowded, generally every 3-4 years. If Iris are allowed to become very crowded, the bloom will suffer. Some varieties may crowd others out and disease problems may be aggravated.

Old clumps may be thinned by removing the old rhizomes at the centers of the clumps and leaving new growth in the ground. Alternately, you may dig up the entire clump and remove and replant the large new rhizomes.

General Garden Care

Keep your Iris beds clean and free of weeds and debris, allowing the tops of the rhizomes to bask in the sun. Bloom stems should be cut off close to the ground after blooming.

Healthy green leaves should be left undisturbed but diseased or brown leaves should be removed. During early/late autumn cleanup the foliage may be cut back to approximately 6 inches. This will help the sun to reach the rhizomes and allow better air circulation around the plants.