The Five Basics of Growing Iris in Containers in the Tucson Area
The container should be at least 15” deep x 12” wide. Diverse types include plastic, which is not porous, and roots will become very hot in the Summer. Concrete containers are too heavy to move but Styrofoam and bamboo are lightweight and may be painted. Talavera or a glazed ceramic is also heavy, but will hold water well, and Mexican clay will crumble with age, but provides air circulation for roots. Italian and Vietnamese clay, wine barrels and stock tanks are other good options.
The soil used in containers must be ‘potting soil’ not ‘garden soil’. Cover the bottom hole with a screen or coffee filter and fill the pot ½ full of soil. Bone meal may be added at this time. Add a 6-10-10 fertilizer (Schreiner’s Natural Based Iris Food or Comanche Acres Iris Food is good) and add soil to within 3” of the top of the pot. Any time-release fertilizer with low Nitrogen (under 10) is best. If possible, prepare your container 2 weeks in advance.
Healthy iris rhizomes are firm and may be planted in a container when you purchase them. If you are unable to plant rhizomes soon, place them in a cool, dry location - but NOT in the refrigerator. The night before planting, soak your rhizomes overnight in water which reaches to the bottom of the rhizome. This will ‘kick start’ growth. When planting, the top of the rhizome should be at the soil line, or slightly below. Iris will not bloom if planted too deep. If the temperature is over 100 degrees after planting, place the pot in a shaded location until temperatures remain under 100. At that time, move the pot to full sun. Next June when the temp reaches 105, move your iris to dappled shade.
Water the soil 2-3 times a week until new leaves appear. The soil should be slightly dry between watering. Use a moisture meter and water when the meter reads ‘dry’. Do not allow the pot to stand in a saucer of water, as it will absorb salts. Elevate your pot with stones if necessary. Drip systems work well. During the summer months, water the soil sparingly in the evenings.
From September through May, fertilizer will be required. Late September through December, apply liquid fish fertilizer monthly. January through May, apply a water-soluble fertilizer monthly, using Miracle Gro 10-51-10, Scotts Super Bloom 12-55-6, or any fertilizer with a middle number of 50 or higher. Follow the instructions on the container. Do not fertilize when your iris are in bloom, nor from June through August.
Attend our local club meetings to learn about the various iris we grow in Tucson. Please visit our website at www.tucsoniris.org for more information.