Prepare the soil:
Irises will thrive in most well drained garden soils. Planting in raised beds or on a slope helps promote good drainage. If your soil is heavy or contains clay, course sand, gypsum, and/or humus may be added to improve drainage and soil aeration. The ideal soil pH is 6.8 (slightly acidic) however; irises will tolerate a range of pH without complaint. If you wish to correct your soil pH, the first step is to have it analyzed. If your soil is acidic - “sour” - lime may be added to “sweeten” it. For alkaline soil, sulfur is added. The soil should be worked up and the garden ready to accept the rhizomes when shipped.
When to plant:
For best results, Iris should be planted in July, August or September. September or October planting may be preferred in areas with hot summers and mild winters. Regardless, it is important that the roots of the newly planted iris be well established before the growing season ends.
Where to Plant:
Irises prefer full sun, but need at least 6 hours of sunshine each day to bloom. In extremely hot climates, some mid day shading is helpful, but in most climates, irises do best in full sun. Avoid low spots where moisture can accumulate. Wet soil can promote bacterial soft rot of the rhizomes. If your soil is wet, planting on a slope or in raised bed will improve the drainage and help avoid rot problems.
How deep to plant:
A common mistake is to plant the rhizomes too deep. Irises should be planted so that the top of the rhizome is exposed to sunlight and the roots are spread out in the soil. Firming the soil over the roots and watering will help to settle the soil and anchor the plant. In very light, sandy soils or in extremely hot climates, a thin layer of soil – less than 1 inch – over the rhizome may be desirable.
Generally, Irises are planted 12 to 24 inches apart. Closer plantings – 8 inches – will provide an immediate “clump” effect, but will need to be thinned and separated more often. Irises should not be allowed to crowd where the rhizomes are forced to grow over the top of other rhizomes.
To establish a healthy root system and viable plant, newly set rhizomes need moisture. Irises should not be kept wet – overwatering is a common error that leads to disease and possible death of the rhizome. Remember – deep, infrequent watering is better than frequent shallow watering. Once they have established, Irises normally do not need to be watered except in arid areas.
Avoid using anything high in nitrogen. High nitrogen will encourage rot problems in the rhizomes. Use only those fertilizers with a low first number (nitrogen content) such as 4-10-10 or 6-10-10. Bone meal is an excellent low nitrogen fertilizer for irises. A light feeding in the early spring and again about a month after blooming will encourage health growth and good blooms. Aged or rotted manure and compost can provide excellent feed; they should be worked into the soil and not be piled around the rhizomes. Avoid using fresh manure or other high nitrogen soil additives.
Ongoing Garden Care:
Iris beds should be kept clean and free of weeds and debris. The tops of the rhizomes should be kept clear so they can enjoy the sun. After blooming, the stems should be cut off close to the rhizome. Healthy green swords should be left undisturbed, but brown and diseased leaves should be removed from the garden. Irises should be thinned and separated every 3-4 years. If the irises are allowed to become overcrowded, they can become stressed and prone to disease. Overcrowding also adversely affects the blooms – resulting in fewer and smaller flowers. Like many perennials, iris may be moved at anytime if proper care is taken. However, the best time to move them is between the time they have finished blooming and the time new growth develops. This is the reason we ship in July, August and September.