Bulbs are often associated with autumn planting for a colorful display the following spring. It is possible to plant bulbs in the spring, but success depends entirely upon the specific type of bulb and local climate conditions. The feasibility of spring planting hinges on correctly identifying whether a bulb is naturally suited for warm-season installation or if it requires special modification to compensate for a missed cold exposure window.
Distinguishing Bulb Types for Spring Planting
Flowering bulbs are generally divided into two main categories based on their hardiness and required planting time. Hardy bulbs, often called spring-blooming bulbs, include varieties like tulips, daffodils, and hyacinths. These require a prolonged period of cold temperatures, known as vernalization, to initiate flower formation. They are typically planted in the autumn so they can undergo this chilling phase naturally over the winter months.
Tender bulbs are frost-sensitive and are meant to be planted in the spring after the threat of cold weather has passed. This group, which includes gladiolus, dahlias, and cannas, produces summer and fall blooms. Since these bulbs do not require a cold period to flower, spring is the optimal and traditional time for planting them into the garden soil.
Planting Hardy Bulbs That Require Chilling
When hardy bulbs such as tulips are not planted in the autumn, they miss the vernalization period required for bloom development. Planting an unchilled hardy bulb directly into warming spring soil generally results in only vegetative growth, producing leaves but no flowers in the current season. This occurs because the reproductive bud within the bulb has not received the necessary cold signal to mature.
To salvage a forgotten hardy bulb, gardeners must artificially replicate the winter cold period before planting outdoors. This involves placing the bulbs in a paper bag or mesh net and storing them in a refrigerator where temperatures remain consistently between 35 and 45 degrees Fahrenheit. The artificial chilling period should last for a minimum of 12 to 15 weeks to mimic the natural winter cycle.
After the required chilling time, the bulbs can be planted outdoors, ideally in a location that receives morning sun and afternoon shade to slow soil warming. Since the bulb has already sprouted internally, the planting depth should be slightly shallower than the standard fall depth, typically burying the bulb only two times its own height. Even with chilling, blooms may be smaller or emerge later than fall-planted counterparts, but the vernalization process makes flowering possible.
Guidelines for Planting Summer-Flowering Bulbs
Spring is the correct time to plant tender, summer-flowering bulbs, but the timing must be precise to avoid frost damage. Planting should only commence once the danger of the last spring frost has passed and the soil temperature has warmed consistently, ideally to at least 60 degrees Fahrenheit. Planting into cold, waterlogged soil can lead to bulb rot before growth begins.
The mechanics of planting these bulbs vary by type, requiring specific attention to orientation and depth. Gladiolus corms, for example, are planted with the pointed side facing upward, typically four to six inches deep to provide stability for the tall stalks that emerge. They should be spaced approximately six inches apart to ensure adequate air circulation.
Dahlia tubers, which are storage roots, are planted horizontally with the growth ‘eye’ or bud facing upward, covered by only a few inches of soil. Caladium tubers, known for their colorful foliage, are usually planted with the knobby side facing up, just one to two inches beneath the soil surface. Proper orientation ensures that the shoot grows upward efficiently and the root structure can anchor effectively.
Spacing is an important consideration to prevent overcrowding and reduce the risk of fungal diseases once the plants mature. Larger bulbs, such as elephant ears (Colocasia), require spacing of up to three feet to accommodate their expansive foliage.
Ensuring Success and Managing Bloom Expectations
Consistent moisture is important for all bulbs planted in the spring to encourage rapid root development and establish the plant before summer heat arrives. After planting, the soil should be thoroughly saturated. Subsequent watering should maintain light moisture without becoming waterlogged, especially in the first few weeks. Incorporating a well-balanced, slow-release fertilizer into the planting hole can provide necessary nutrients, but avoid direct contact with the bulb itself to prevent chemical burn.
Gardeners must maintain realistic expectations for bulbs planted late in the season, particularly hardy types that were artificially chilled. Blooms from spring-planted hardy bulbs are often smaller, less numerous, or appear several weeks later than those planted the previous fall. The plant’s energy is redirected to catching up on the missed growing window.
For all bulb types, allow the foliage to fully yellow and die back naturally before cutting it. The leaves are the plant’s food factory, performing photosynthesis to store energy in the bulb for the following season’s growth. Removing green leaves prematurely limits the bulb’s ability to recharge, potentially sacrificing future blooms.