The term “blue rain plant” is a descriptive phrase, often used to refer to various plants that produce cascading blue flowers. While several species might fit this aesthetic, the most commonly associated plant, and the primary focus for achieving a dramatic “blue rain” effect, is Wisteria. This article will clarify what plants fall under this evocative description and provide comprehensive care instructions, with a particular emphasis on Wisteria.
Identifying “Blue Rain Plants”
Wisteria is widely recognized as a “blue rain plant” for its spectacular, long, pendulous flower clusters, creating a waterfall of color. There are several popular species, including Wisteria sinensis (Chinese wisteria), Wisteria floribunda (Japanese wisteria), and Wisteria frutescens (American wisteria). Wisteria sinensis is known for its vigorous growth and flowers that emerge before its leaves, while Wisteria floribunda features even longer flower racemes, some reaching up to 7 feet, and blooms as its leaves appear. Wisteria frutescens is a less aggressive native species, typically producing shorter flower clusters after its leaves emerge.
Other plants sometimes referred to as “blue rain plants” share the characteristic of blue or purplish cascading blooms, though often on a smaller scale or with a different growth habit. Plumbago (Plumbago auriculata), also known as Cape Leadwort, is a sprawling shrub or vine with sky-blue, phlox-like flowers that bloom over a long season. Browallia (Browallia speciosa), or Amethyst Flower, is a bushy perennial often grown as an annual, producing star-shaped, purplish-blue flowers. These plants offer similar blue hues but are distinct from Wisteria in their overall form and cultural needs.
Cultivating Wisteria (The Primary “Blue Rain Plant”)
Successful Wisteria cultivation begins with site selection. It thrives in full sun, requiring at least six hours daily for optimal flowering. Partial shade is tolerated, especially in warmer southern climates, but may reduce flowering.
The plant prefers well-drained, fertile soil with a slightly acidic to neutral pH. Good drainage is important, as Wisteria does not tolerate waterlogged conditions. Incorporating organic matter improves soil fertility and drainage.
Consistent moisture benefits young Wisteria during establishment, typically requiring one inch of water weekly. Once established, Wisteria becomes more drought-tolerant but benefits from deep watering during prolonged dry periods. A 2-3 inch layer of organic mulch around the base helps retain soil moisture and suppress weeds.
Fertilization should be cautious, as excessive nitrogen promotes leafy growth over flowers. If soil is poor, apply a balanced fertilizer or one higher in phosphorus (e.g., 5-10-10 or 5-10-5 blend) in early spring. Wisteria generally performs well without heavy fertilization due to its nitrogen-fixing ability.
Wisteria is hardy in USDA zones 5-9. It can be susceptible to pests like aphids, spider mites, and scale, causing leaf yellowing or stunted growth. Diseases such as powdery mildew and leaf spot may also occur, appearing as white coatings or dark spots. Regular inspection and good air circulation help manage these issues.
Pruning and Training Wisteria for Optimal Blooms and Growth
Pruning is essential for managing Wisteria’s vigorous growth and encouraging abundant flowering. Without it, Wisteria becomes an unruly mass of foliage with few blooms. Pruning directs the plant’s energy towards developing flower buds, not excessive vegetative growth.
Wisteria requires two main annual pruning sessions: one in summer and another in winter. Summer pruning, typically in July or August after flowering, involves cutting back the current year’s long, whippy green shoots. Reduce these to five or six leaves from the main branch or framework. This controls plant size and promotes flower bud formation for the following season.
Winter pruning occurs during the dormant season, usually January or February, when the plant is leafless. Shorten the summer-pruned shoots to two or three buds from the older wood. This encourages flowering spurs and ensures blooms are not obscured by foliage. Winter is also ideal for removing dead, damaged, or overcrowded branches.
Training Wisteria onto a sturdy support structure is crucial due to its heavy, twining stems. Pergolas, arbors, or robust trellises are suitable, as they withstand the plant’s considerable weight. When training, select a few strong main stems near the base and loosely tie them to the support as they grow vertically. As the plant reaches the top, guide lateral stems along horizontal beams, tying them at intervals for even coverage and the desired ‘raining’ effect.
Important Considerations for “Blue Rain Plants”
Wisteria is toxic. All parts, especially seeds and pods, are toxic to humans and pets if ingested, causing severe discomfort. Exercise caution, especially around children and and animals.
Wisteria’s vigorous growth can be both a benefit and a challenge. While rapid growth quickly covers large structures, some species, particularly Chinese and Japanese wisteria, can be aggressive and invasive. Their strong twining stems can girdle and damage host trees or structures if not properly managed. Responsible planting involves selecting less aggressive species like American wisteria and maintaining consistent pruning to contain spread.
Wisteria can be propagated through softwood cuttings in late spring or early summer. Seeds can also be used, though plants grown from seed may take many years to flower and may not reliably produce desired characteristics. Layering is another viable propagation technique.