Iris Care
When To Plant Iris
Where To Plant Iris
How To Plant Iris
Fertilizing Iris
Pests and Diseases
- For best results, plant iris rhizomes in July, August or September. This is also the best time, as plants are normally dormant during the heat of July and August, to divide and replant iris that have become overcrowded, usually after three to five years.
- It is important that the roots of newly planted iris be well established before the end of the growing season. Plant your iris at least four to six weeks before your first hard freeze or killing frost.
Where To Plant Iris
- Iris do best in well-drained soil. A raised bed or planting on a slope are ideal places to plant iris. Good air circulation is essential and water should not stand in beds.
- Iris require at least a half-day of direct sunlight. Some afternoon shade is beneficial in extremely hot climates, but in general iris do best in full sun. Iris will grow in deep shade, but probably will not bloom.
How To Plant Iris
- Plant your rhizomes at or just barely below the ground. Build up a small mound of soil in the center of the planting hole. Center the rhizome on the soil mound and spread out the roots on either side. Firm the soil around the roots. Newly planted rhizomes should be watered thoroughly.
- Planting rhizomes 12 to 24 inches apart is the norm. Close planting results in an immediate effect, faster clump formation, and more color, but makes dividing clumps a necessity in two to three years.
- Newly planted rhizomes need moisture so their root systems develop. Once established, irises should be watered when the top 3 inches of soil dry out. The watering frequency will depend to a great extent on your environment. Over watering is a common mistake.
Fertilizing Iris
- The soil type for your area will determine your fertilizer needs. Superphosphate or a well-balanced fertilizer of an N-P-K ratio 5-10-10 are recommended. Avoid anything high in nitrogen as it encourages soft growth that is susceptible to disease. Provide a light application in early spring and again a month after bloom. Place fertilizer around rhizomes, not directly on them. Alfalfa pellets (without salt) are extremely beneficial when incorporated in the soil around the newly planted irises. Do NOT use Feed & Weed preparations or Miracle Grow.
Pests and Diseases
- Leaf spot
- Bacterial – occurs during mild, foggy and rainy weather.
- Fungal – the more rain you have, the more prevalent it becomes. Easy to control with a fungicide like Daconil.
- Crown Rot
- Excessive moisture can lead to crown rot. It is important that you remove the rotting tissue as soon as you can. Remove the soil from around the rhizome, leaving the roots anchoring the plant. Using an old spoon, carefully scoop out all the mushy tissue. If necessary, dig up the entire plan and remove the rotten tissue. After removing the tissue, drench the wounds with a 10% solution (1 part bleach to 9 parts water) and allow them to dry for several days before covering with soil again.
- Iris Borer
- Iris borers overwinter as eggs on both iris and other types of plant debris. Eggs hatch in early May and larvae bore into leaves, often leaving a water-soaked spot. Larvae tunnel down through the leaves and eventually reach the rhizomes below ground. Larvae move into soil and pupate. Adult cutworm moths emerge and lay eggs in late August and September.
- Control: Remove old plant debris near iris plants to destroy overwintering sites for borer eggs. While important for controlling iris borer, this technique will not always eliminate iris borer problems. In the spring, watch for small (approximately ¼ inch long) larvae as they begin to tunnel into iris leaves. These small larvae can be crushed by hand. If you decide to use an insecticide for control, select a product that contains azadirachtin, pyrethrins, permethrin or Spinosad. Insecticides must be applied before iris borer larvae tunnel deep into the plant. Therefore, first sprays should be applied when new iris shoots are four to six inches long, and a second application should be applied 10 to 14 days later. Be sure to read and follow all label instructions of the insecticide that you select to insure that you use the product in the safest and most effective manner possible. Products containing the parasitic nematodes Heterorhabditis or Steinernema also have been successful in controlling iris borer larvae when used as soil drenches in June and early July.
- Aphids
- Aphids suck the sap out of plants and can transfer diseases. This may cause your iris to become deformed or die.
- How do you kill aphids naturally? Make a homemade insecticidal soap, a low-toxicity bug control solution that will desiccate the soft bodies and kill the aphids without doing harm to your plants. Simply mix a few teaspoons of Dawn dish soap with one quart of water, then spray or wipe the solution onto the leaves, stems and buds of the plant.
- You can also try planting garlic or onion plants nearby the infested plants. The smell of these plants drives the aphids away. You can plant garlic and onions in pots for mobile homemade aphid control.