The Cosmic Crisp apple, officially known as the WA 38 cultivar, is a relatively new variety developed through the apple breeding program at Washington State University (WSU). This apple is a cross between ‘Enterprise’ and ‘Honeycrisp,’ celebrated for its remarkable crispness, deep red skin marked with distinctive white lenticels, and exceptional storage life. Successfully growing the Cosmic Crisp at home requires understanding its specific environmental and horticultural needs. Achieving a successful harvest depends heavily on meeting the tree’s requirements for temperature exposure, soil conditions, sunlight, and proper maintenance.
Defining the Cosmic Crisp Hardiness Zone
The geographic area suitable for growing the Cosmic Crisp is primarily defined by its cold tolerance and chilling requirement. Most nurseries list the WA 38 as reliably hardy in United States Department of Agriculture (USDA) Hardiness Zones 5 through 9. The tree’s cold hardiness is often influenced by the specific rootstock it is grafted onto, such as M9, M26, or MM106, which determine the tree’s mature size and overall vigor.
The most significant environmental constraint is the cultivar’s need for a period of winter dormancy, measured in chill hours. Chill hours are the cumulative number of hours the tree is exposed to temperatures between 32°F and 45°F (0°C and 7°C) during the winter months. The Cosmic Crisp requires an estimated 600 or more chill hours to properly break dormancy, which ensures a robust spring bloom and subsequent fruit set. If the tree does not receive enough chilling, it may experience delayed or uneven bud break, poor flower development, and a significantly reduced fruit yield. This requirement means that while the tree may survive in warmer Zone 9 areas, the lack of sufficient cold temperatures may prevent it from producing a harvest.
Essential Soil and Sunlight Requirements
A successful planting site must provide the correct physical environment, starting with appropriate soil and sufficient light. The WA 38 cultivar requires a location that receives full sun, which translates to a minimum of six to eight hours of direct sunlight per day. Adequate light penetration is important for this bi-color apple, as sunlight is necessary for the fruit to develop its desirable deep red color.
The preferred soil composition is well-draining, loamy, and rich in organic matter to support the tree’s vigorous growth. Poor drainage is a serious issue for apple trees, as standing water can lead to root rot and eventual tree death. Growers should aim for a slightly acidic to neutral soil pH, ideally ranging between 6.0 and 7.0, as this range optimizes the availability of nutrients. At planting, the graft union—the slight bulge where the cultivar meets the rootstock—must be positioned at least one inch above the finished soil surface to prevent the scion wood from developing its own roots.
Ensuring Fruit Production: Pollination and Pruning
Once the tree is established, successful fruit production relies on careful horticultural practices regarding pollination and canopy management. The Cosmic Crisp is not self-pollinating and requires a suitable cross-pollinator to be planted nearby, ideally within 50 feet. The chosen pollinator must be an apple or crabapple variety that blooms at the same time as the WA 38, which is a mid-to-late season bloomer, generally in flowering group 4. Recommended cross-pollinators include varieties like Gala, Fuji, or Honeycrisp, or late-flowering crabapples such as Snowdrift or Mt. Everest.
Proper pruning and training are necessary to manage the WA 38’s naturally vigorous growth habit and tendency to produce “blind wood,” which are sections of branch without flower buds. Techniques like click pruning—tipping one-year-old wood—are recommended to manage vigor and induce bud swelling, encouraging more uniform fruit growth. Pruning should create an open canopy that allows maximum light penetration and air circulation, which is necessary for fruit color development and overall tree health. Home growers should be patient, as the Cosmic Crisp typically takes three to five years after planting to begin bearing a significant crop.