The ‘Blue Moon’ Wisteria (Wisteria macrostachya ‘Blue Moon’) is a deciduous woody vine prized for its spectacular display of fragrant, lavender-blue flowers. This American native cultivar, often called Kentucky Wisteria, is much more manageable for the home gardener than its aggressive Asian cousins. It exhibits exceptional cold tolerance, thriving reliably in USDA Hardiness Zones 3 or 4, making it one of the hardiest wisterias available. This selection is also known for its reliable, earlier flowering habit and its ability to rebloom in the summer, providing a longer season of color.
Site Selection and Support Structures
Selecting the correct location is the first step toward cultivating a healthy and vigorously blooming ‘Blue Moon’ Wisteria. This vine requires a minimum of six hours of direct sunlight daily; planting in full sun ensures the best flower production, as shaded conditions reduce the number of blooms. The soil should be well-drained and slightly acidic, ideally with a pH range between 6.0 and 7.0. Amending the soil with compost will improve its structure and fertility.
When planting, dig a hole two to three times the width of the root ball but no deeper than the container. If the plant is grafted, the visible graft union should be positioned slightly below the soil surface to encourage the scion to develop its own roots. After placing the root ball, backfill the hole with soil, tamping gently to remove air pockets, and water thoroughly.
Because ‘Blue Moon’ is a vigorous climber capable of reaching 20 to 30 feet, it requires a permanent, robust support structure from day one. A sturdy arbor, pergola, or heavy-duty trellis is necessary to bear the considerable weight of a mature vine, as it can break weaker supports. The vine naturally twines counterclockwise, so it should be loosely tied to the support initially, training a central leader to establish the main framework.
Watering and Fertilization Schedule
Young ‘Blue Moon’ Wisteria plants need consistent moisture to develop a strong, deep root system during their first two seasons. Deep watering once a week is recommended, especially during dry weather, ensuring the entire root zone is saturated. Once established, the vine becomes drought-tolerant, relying mostly on natural rainfall. Supplemental watering may still be needed during prolonged summer dry spells.
The most important factor in fertilization is avoiding high-nitrogen formulas, which promote lush green growth at the expense of flower development. Wisteria is a legume and naturally fixes its own nitrogen in the soil through a symbiotic relationship with bacteria. Instead of nitrogen, the vine benefits from a fertilizer high in phosphorus and potassium, which support blooming and overall plant health.
Applying a high-phosphorus product, such as superphosphate or a balanced fertilizer with a high middle number (e.g., 10-20-10 or 0-10-10), in early spring helps stimulate flower bud production. This application should be scratched lightly into the soil around the base of the plant before new growth begins. Bone meal is a slow-release organic option that also provides the necessary phosphorus to encourage a spectacular floral display.
Pruning for Optimal Flowering
Pruning is the most important practice for ensuring heavy, consistent flowering and controlling the vine’s aggressive growth habit. ‘Blue Moon’ Wisteria requires two distinct pruning periods: a summer prune and a dormant winter prune. This two-step process directs the vine’s energy toward creating flower buds, known as spurs, rather than producing long, leafy tendrils.
The first pruning occurs in mid-to-late summer, about a month after the initial flowering period finishes. The long, whippy, new vegetative shoots that emerged are cut back sharply. These growths should be reduced to five to six leaves from the main, established woody framework. This initial cut reduces the bulk of the foliage, allowing more light and air to reach the inner structure and concentrating energy into the remaining buds.
The second, more precise pruning takes place during late winter dormancy, typically in January or February. This involves returning to the shoots cut back in summer and further reducing them to two or three buds. These remaining short spurs are the locations where the following season’s flower clusters will form. This consistent, severe reduction of new growth forces the vine to stop producing long, unproductive runners and focus on developing the short, thick flowering wood.
Maintaining a strong, well-defined woody framework is the goal of this annual, two-part pruning regimen. Any dead, diseased, or crossing branches should be removed during the winter pruning to improve the overall structure and health of the vine. Consistent training and pruning also prevent the vine from becoming a dense tangle of stems, which makes future maintenance difficult and reduces air circulation, preventing disease issues.
Addressing Pests and Bloom Failure
While ‘Blue Moon’ Wisteria is robust, it can occasionally encounter typical garden pests, including aphids, scale insects, and the potato leafhopper. Aphids are small, soft-bodied insects that cluster on new growth, causing leaves to curl and leaving behind a sticky residue called honeydew. Scale insects appear as small, hard bumps on stems and leaves, sucking sap and weakening the plant.
Minor aphid infestations can be managed by spraying the affected areas with a strong jet of water to dislodge the insects. For persistent issues with aphids or scale, an application of insecticidal soap or horticultural oil, such as neem oil, can be effective, provided it coats all surfaces of the pests. Ensuring the vine has adequate air circulation through proper pruning helps deter common fungal diseases like powdery mildew.
The most common concern is the failure of the wisteria to produce blooms, which can be attributed to several factors beyond improper pruning. If a young vine is not flowering, the cause is often simple immaturity, as even this cultivar may take three to five years to become established and bloom. A non-blooming vine may also be receiving too much nitrogen fertilizer, which encourages excessive foliage growth.
The lack of blooms can also result from insufficient light, so ensuring the vine receives full sun exposure is important, especially if surrounding trees or shrubs have grown larger. Late spring frosts can damage newly formed flower buds, leading to a year with few or no flowers. In this case, wait for the plant to recover and set new buds for the following season.