We Pacific Giant Delphiniums are sun worshippers at heart. To produce our towering, magnificent spires of bloom, we require a location with full sun, meaning at least 6 to 8 hours of direct sunlight daily. In regions with extremely intense afternoon heat (USDA zones 8 and above), we appreciate some light afternoon shade to protect our foliage from scorching. We thrive in cooler climates and are happiest when nights are cool. Our ideal growing temperatures are between 65°F and 75°F (18°C - 24°C) during the day and cooler at night. High heat and humidity are our biggest challenges, often shortening our lifespan and making us susceptible to disease.
Our roots are particular; they demand excellent conditions to support our great height. We require deeply worked, rich, and fertile soil that is consistently moist but never, ever waterlogged. Excellent drainage is absolutely non-negotiable for us, as our crown will quickly rot in soggy conditions. A neutral to slightly alkaline soil pH is our preference. Before planting, please amend the soil generously with well-rotted compost or manure. This provides the nutrients we crave and improves both moisture retention and drainage—a perfect balance for our needs.
Maintaining consistent moisture is key to our success. We have a deep root system but dislike drought intensely. Water us regularly, providing about 1 inch of water per week, more during hot, dry spells. Always water at the base to keep our foliage dry and prevent disease. As heavy feeders, we need ample nutrition. Feed us in early spring as we emerge with a balanced, slow-release fertilizer. Then, feed us again as our flower spikes begin to form to support the tremendous energy required for blooming. A final feeding after you cut back our first spent flower spikes will encourage a second, smaller bloom later in the season.
Our flower spikes are incredibly heavy and we are notoriously top-heavy. Without proper support, a gust of wind or a summer rainstorm can snap our stems at the base. Please install sturdy stakes (bamboo or metal) around us early in the season, before we get too tall. As we grow, gently tie our main spikes to the stakes every 12-18 inches using soft ties. To prolong our blooming, deadhead our spent flower spikes by cutting them back to a side shoot or to the base of the plant. This often convinces us to produce a second, smaller flush of flowers.
It is important to understand that we are short-lived perennials. In perfect conditions, we may live 2-3 years, but we are often treated as biennials or annuals, especially in warmer parts of the US. Our main adversaries are slugs and snails, which find our new spring growth irresistible. Powdery mildew can also be an issue in humid climates with poor air circulation. To combat this, ensure we have adequate spacing and practice watering at the soil level. After the first hard frost in autumn, you can cut our foliage down to the ground. A light winter mulch applied after the ground freezes can help protect our crown, but be sure to remove it early in spring to prevent rot.
