Irises are perennial flowers celebrated for their striking, orchid-like blooms and vibrant colors. Most varieties do not bloom all summer; they follow a distinct, relatively short annual bloom cycle. However, modern hybridization has introduced specific types, known as rebloomers, that can extend the flowering season far beyond the typical spring display. Understanding the difference between these two categories is key to enjoying irises for a longer period.
The Typical Iris Blooming Season
The vast majority of irises, including popular Tall Bearded varieties, are monophasic bloomers, flowering only once per year. This peak season typically occurs in late spring to early summer, generally spanning from May through June, depending on the climate and cultivar. Individual flowers on a single stalk open sequentially, each lasting only a few days before fading. The entire flowering cycle for one established clump is brief, lasting around two to four weeks in total. Most garden irises spend the rest of the summer storing energy in their rhizomes for the following year’s display.
Identifying Irises That Bloom More Than Once
Varieties that extend the bloom season are classified as Remontant irises, a term derived from the French word meaning “to ascend again.” These rebloomers possess a genetic trait allowing them to produce multiple flushes of bloom stalks within a single growing season. Unlike standard irises, which require winter cold (vernalization) to initiate the next bloom cycle, Remontant irises bypass this requirement, accelerating their growth to produce secondary or tertiary sets of flowers.
Rebloomers are most commonly found among Bearded Iris types, particularly Tall Bearded hybrids, but the capacity for repeat flowering is not exclusive to them. Some Siberian or Louisiana irises may occasionally exhibit this trait, though it is less common and reliable. Remontancy manifests in different patterns; some are “cycle rebloomers,” producing a spring flush followed by a distinct autumn flush. Others are “all-season rebloomers” that produce flowers sporadically throughout the summer and fall months. The success and timing of these additional blooms depend heavily on local conditions.
Cultivating Repeat Blooms
Encouraging a Remontant iris to produce second and third bloom cycles requires more attention to cultural practices than standard iris care. Since these plants are flowering repeatedly, they require a steady supply of resources. Prompt deadheading of spent bloom stalks after the initial spring flowering is important. This action conserves the plant’s energy by preventing it from diverting resources into seed production.
Fertilization
Remontant irises are heavy feeders and benefit from an adjusted fertilization schedule. They require additional nutrients, particularly fertilizer higher in nitrogen and phosphorus, to fuel the growth of new fans and subsequent flower stalks. Applying a balanced fertilizer, such as a 5-10-10 blend, after the first spring bloom and again in mid-summer helps ensure reserves for rebloom. Apply the fertilizer around the rhizomes, rather than directly on them, to prevent burning the storage organ.
Watering and Climate
Maintaining consistent moisture is necessary for rebloomers, especially during dry summer months. While standard irises prefer a drier period after their spring bloom, rebloomers need regular watering to support continuous growth and flower development. Allowing the soil to become too dry can trigger a dormancy period, stopping the production of new flower stalks. However, the soil must still be well-draining, as rhizomes are susceptible to rot if they sit in standing water.
The climate also plays a significant role in the success of reblooming varieties. They perform best in regions with mild winters and long, warm growing seasons, such as USDA Zones 6 and warmer. Extended warmth provides the time and energy for the plant to fully recover from the first bloom and initiate floral structures. In cooler climates, rebloom may be less predictable and often limited to a late summer or early fall appearance.