The appearance of iris seed pods marks the conclusion of the vibrant blooming season, presenting a choice for the gardener. A seed pod is the swollen, three-sided capsule that develops on the flower stalk once the bloom has faded and been successfully pollinated. These pods start small and green, expanding throughout the summer months as the seeds inside mature. Whether you leave these capsules to ripen or remove them determines how the plant allocates its remaining energy.
Immediate Post-Bloom Care and Removal
If propagation is not the goal, the best practice is to remove the spent flower head immediately, a process known as deadheading. This action prevents the plant from diverting energy resources into seed production. By eliminating this reproductive effort, the plant can instead focus its energy reserves on strengthening the rhizome, the root structure that fuels future growth and blooms.
The entire flower stalk, or scape, can be left in place after the flowers have faded and been removed. This green stalk continues to perform photosynthesis, contributing energy back to the rhizome. Gardeners often choose to cut the entire stalk back to the ground later in the season for aesthetic reasons or to minimize the risk of fungal diseases like botrytis.
Removing the stalk is recommended once it turns yellow or soft, usually a few weeks after the last flower has dropped. The initial removal of the withered flower and the green sheath behind it is sufficient to stop seed formation. For reblooming varieties, this redirection of energy can encourage a second flush of flowers later in the year.
Harvesting Iris Seeds for Propagation
For the gardener interested in growing new, genetically unique iris plants, the pods must be left on the stalk to mature fully. Harvest usually occurs two to three months after the flower has bloomed, typically in mid-to-late summer. A mature pod is distinguished by its color change from green to a dry, tan, or brown hue.
The most precise indicator of ripeness is when the capsule begins to crack or split open along its seams. It is important to collect the pods just before they fully open to prevent the seeds from spilling onto the soil. The seeds themselves should be firm to the touch and possess a hard, dark brown, or tan exterior.
Once harvested, the pod is cracked open, and the seeds are separated from any chaff or capsule material. These seeds should be spread out in a single layer in a cool, dry, and dark location for several weeks to cure completely. Proper drying and storage in a labeled paper envelope are important for maintaining viability until planting preparations begin.
Preparing Seeds for Planting and Germination
Iris seeds possess a dual form of dormancy, which makes germination challenging without specific preparation. The hard outer shell, or seed coat, can be impermeable to water, and the seed also contains a chemical inhibitor that suppresses sprouting. To overcome this, the seeds require a period of cold, moist conditioning known as cold stratification.
Many gardeners opt for natural stratification by sowing the seeds directly outdoors in late fall or early winter. Planting the seeds about a half-inch deep in a well-drained medium allows the natural freeze-thaw cycles and winter moisture to soften the seed coat and leach out the inhibitor. This natural process mimics the conditions the seeds would experience in the wild, leading to germination in the following spring.
For a more controlled approach, artificial stratification involves placing the seeds in the refrigerator for 6 to 14 weeks. The seeds should first be soaked in water for up to two weeks, changing the water daily, to begin removing the germination inhibitor. The soaked seeds are then placed in a sealed bag with a moist medium, such as peat moss or vermiculite, and kept chilled.
After the chilling period, the seeds can be sown in pots filled with a sterile seed-starting mix and kept in a warm, bright location. The combination of initial soaking and the subsequent cold period is necessary to break the deep dormancy of the seeds. While iris grown from rhizomes bloom quickly, seedlings started this way may take two to three years to produce their first flower.