When to Plant
For best results, plant your iris from July through September. You want to establish the new rhizomes before winter sets in. Plant at least 4 to 6 weeks before frost in areas with harsh winters.
This is also the time to dig and divide any existing crowded clumps.
Where to Plant
Bearded iris love the sun and need at least six hours of sun to flower. Plant your iris in a well-drained location. Iris rhizomes will rot if left in standing water. You may need to create raised beds or plant on a slope to ensure good drainage.
Soil Preparation
Iris will thrive in most well-drained garden soils. Planting on a slope or in raised beds helps ensure good drainage. Our local soil generally is clay soil. Add organic matter (compost) to improve soil drainage. This allows roots to have the air and water they need to thrive.
Planting Depth
Plant your iris so the tops of the rhizomes receive light from the sun. Spread the roots out and downward in the soil. If you have light soil or your climate is scorching, you may cover the rhizomes with an inch of soil. If planted too deep, iris may not flower.
Firm the soil around each rhizome. Water to settle the soil. Keep the soil moist, not soggy, until the plant shows leaf growth.
Planting Distance
Iris are generally planted 12 to 24 inches apart. Create an immediate clump by planting three rhizomes of one variety in a triangle. Point the rhizomes inward spaced about 8 inches apart. Iris planted closer together will need dividing more often.
Watering
Recently planted iris need moisture so they can grow a new root system. Keep these rhizomes moist, but not soggy, until you see leaf growth. Your climate and soil will affect how often you water. Deep watering at longer intervals is better than frequent shallow watering. Established plants don’t need watering unless in arid areas. Avoid overwatering your iris.
Fertilizing
Iris may thrive without feeding depending on your soil type. Any application of fertilizer should be light. Use a balanced fertilizer (such as 5-5-5). Avoid using anything high in nitrogen. Nitrogen encourages root rot.
You may fertilize:
- At planting – work a bit of fertilizer into the planting hole below the rhizome’s roots.
- Early spring, very late fall, and after bloom – work fertilizer around and between plants.
Dividing Iris
Over time, iris rhizomes become crowded. This can lead to reduced flowering. Some varieties may get crowded out. Crowding can also lead to disease. Dividing the clumps can help restore the health of the plants. You need to dig and divide the clumps every 3 to 4 years.
Dig the clumps up with a rounded shovel or a spade fork. Dig well under the rhizomes. Separate the rhizomes with a sharp knife. Cut off spent rhizomes and any diseased parts. Trim leaves back halfway into a pointed fan shape. Trim the roots down to 4 to 6 inches. Soak the rhizomes for 10 minutes in a 10% bleach solution. Rinse and let rhizomes dry in the shade. Replant the largest rhizomes.
General Garden Care
Keep your iris beds clean and free of weeds and debris. Garden litter around your rhizomes could induce rot or disease. Cut bloom stalks off close to the ground after blooming. Don’t trim green healthy leaves. Cut off and remove any brown or diseased leaves.
