Ranunculus (Ranunculus asiaticus) are prized for their exquisitely layered, rose-like blooms. However, they are not traditionally considered hardy in the colder growing zones of the northern United States (typically USDA zones 3-6). They thrive in cool conditions but are susceptible to freezing, wet soil which causes their tuberous roots to rot. Therefore, successful cultivation in the North relies heavily on selecting the right varieties and employing specific planting strategies, primarily treating them as annuals or lifting them for winter storage.
While most ranunculus varieties share similar growing needs, some series and types have proven to be more vigorous and reliable in the shorter, cooler growing seasons of the North.
Bloomingdale Series: This dwarf strain is an exceptional choice for northern gardeners. Its compact size (8-10 inches tall) makes it less vulnerable to wind and weather damage. It blooms prolifically and is known for its early flowering habit, a significant advantage in regions with a shorter frost-free window. It performs brilliantly in containers, which can be moved to sheltered locations during unexpected late or early frosts.
Cloni Success Series: Bred for the cut flower industry, these varieties are selected for their strong stems, large flower size, and incredible vigor. This robustness translates well to northern gardens, as healthier plants are better equipped to handle temperature fluctuations. They offer the widest range of colors, including stunning bicolors, and are the premier choice for gardeners focused on creating lavish bouquets.
Techo Series: Similar to the Bloomingdale series, the Techno ranunculus are compact, early-flowering, and free-blooming. Their resilience and ability to produce a high volume of flowers on a small plant make them ideal for border edges, patio pots, and small-space gardens where they need to put on a quick and dramatic show.
The variety is only part of the equation; proper technique is crucial for success.
Pre-sprouting Tubers: This is the most critical step for northern zones. Start tubers indoors 12-14 weeks before the last expected frost. Soak them for 3-4 hours and then plant them in moist, well-draining potting mix. Place them in a cool (50-60°F), bright location. This head start allows you to transplant robust, already-growing plants outdoors as soon as the soil is workable, maximizing the growing season.
Soil and Site Requirements: Plant pre-sprouted ranunculus in full sun in soil that has been amended with compost to ensure excellent drainage. Raised beds are highly recommended in northern zones to prevent waterlogging from spring rains. Ensure the planting site is sheltered from strong winds that can damage the tall flower stems of some varieties.
Fall Considerations: In zones 6 and perhaps a protected zone 5b, a thick layer of mulch (like straw or shredded leaves) applied after the ground freezes may allow tubers to survive winter in the ground. However, in zones 5 and colder, it is safest to treat them as annuals or carefully lift the tubers after the foliage dies back. Dry them thoroughly, store them in a cool, dry, frost-free place in peat moss or vermiculite, and replant them the following spring.
