The mild, marine climate of the Puget Sound region, characterized by wet, cool winters, offers ideal conditions for bulb gardening. While this climate avoids the deep freeze common elsewhere, the persistent moisture presents a challenge that can lead to bulb rot. Successful bulb growth in Seattle depends on accurate planting timing and meticulous preparation of the often-dense native soil. Understanding the requirements of spring-blooming and summer-blooming varieties is key to a vibrant garden display.
Seasonal Timing for Bulb Planting
Bulb planting timing is divided into two main categories: spring-blooming and summer-blooming. Spring-blooming bulbs, such as tulips, daffodils, and hyacinths, require a period of cold dormancy, known as vernalization, to initiate flowering. This cold period must occur naturally in the ground during the winter months.
The ideal window for planting spring varieties is from late September through November, before the soil temperature drops below 55°F. Planting should occur when nighttime air temperatures are consistently in the 40s, signaling the soil is cooling down but is not yet frozen. Planting too early, while the soil is still warm, can cause bulbs to sprout foliage prematurely. This diverts energy needed for root development and successful spring flowering.
Conversely, summer-blooming bulbs like dahlias, gladiolus, and begonias are tender and cannot survive a Puget Sound winter. These are planted in the spring, after all danger of a hard frost has passed and the soil temperature has warmed. Planting usually occurs in late April or May, when the soil reaches at least 60°F.
The last expected frost date for the Seattle area generally falls around late March. Waiting until mid-to-late spring ensures the tender bulbs are not exposed to damaging cold snaps. This allows them to focus their energy on producing lush growth and flowers throughout the summer and fall.
Preparing Soil and Site Selection
Native Seattle soil is frequently heavy clay, which retains water and lacks the necessary pore space for drainage. Since bulbs rot if they sit in cold, saturated soil during the wet winter, improving drainage is the most important preparatory step. Waterlogging displaces the air pockets essential for healthy root development and oxygen uptake.
To amend heavy clay soil, incorporate organic matter rather than adding sand, which can create a concrete-like mixture. Work in materials like compost, fine fir or hemlock bark, or leaf mold to a depth of 8 to 12 inches. These amendments should make up to 30% of the native soil volume, creating air spaces that allow water to drain freely.
Proper planting depth is essential for successful growth. A general rule is to plant the bulb two to three times its height deep, measuring from the base of the bulb. For example, a two-inch tulip bulb should be covered with four to six inches of soil. Adequate spacing is also necessary, typically three to six inches apart for larger bulbs like daffodils, to allow for future offsets and proper air circulation.
Site selection should prioritize sun exposure based on the bulb type. Most spring-blooming bulbs, such as tulips and daffodils, thrive in full sun, which is six or more hours of direct light daily. Planting them under deciduous trees works well since they bloom before the tree canopy fully leafs out. Summer bloomers like dahlias require full sun throughout their growing season.
Post-Planting Care in the Maritime Climate
Immediately after planting, water the bulbs thoroughly one time to settle the soil around them and initiate root growth. After this initial watering, the maritime climate’s consistent rainfall usually provides sufficient moisture throughout the fall and winter. The focus during the rainy season shifts to ensuring the planting site never becomes waterlogged, which is the primary cause of bulb rot.
Gardeners can apply a low-nitrogen, high-potassium fertilizer once in early spring when the first shoots emerge from the soil. This timing supports the development of the flower bud and root system without encouraging excessive leaf growth. Slow-release, granular fertilizers formulated specifically for bulbs are an easy-to-apply option.
The damp environment of the Pacific Northwest is an ideal habitat for slugs, which can damage emerging shoots. Control methods include placing copper tape barriers around raised beds, or using iron phosphate pellets, which are generally safe for pets and wildlife. Regularly hand-picking slugs, particularly after dark or in the early morning, is another effective way to reduce the population.