A true bulb (e.g., tulip or daffodil) is a compact, underground storage unit. It contains the entire embryonic plant, wrapped in fleshy scales that hold food reserves to fuel initial growth and the bloom cycle. Proper planting orientation is necessary for efficient growth, ensuring the shoot grows upward toward the light and the roots grow downward into the soil. If planted incorrectly, the emerging shoot must expend significant stored energy to reorient itself, which can result in a delayed or smaller flower.
Identifying the Correct Orientation
The general rule for planting a standard bulb is to place the pointy side up. This growing tip, or “nose,” is where the stem and flower will emerge. The opposite, flatter end is the basal plate, where the roots develop and must face down into the soil. For common bulbs like tulips, this distinction is clear due to their conical shape.
The basal plate often has dried, fuzzy remnants of old roots, providing a clear visual cue. If the tip is less defined or the bulb is damaged, it is acceptable to plant it on its side.
The plant’s natural response to gravity (gravitropism) causes the shoot to curve and grow upward. While this uses more energy than a perfectly planted bulb, it ensures growth. Planting a bulb upside down uses the most energy and may result in a weakened bloom in the first year.
Preparing the Planting Site
Assessing the planting site’s conditions is necessary for the bulb’s long-term health. Bulbs are prone to rot, so well-drained soil is required to prevent excessive moisture. If the existing soil is heavy clay, adding organic material such as compost or coarse grit will improve drainage and aeration.
Bulbs require cold dormancy and will rot in wet soil. Soil amendments provide slow-release nutrients after the stored energy is depleted. Bone meal is a traditional amendment often mixed into the planting hole, as it provides phosphorus for strong root development.
Sunlight is also a factor. Most spring-flowering bulbs, such as daffodils, perform best in full sun to partial shade. It is better to rely on a balanced, slow-release bulb fertilizer than bone meal alone, as bone meal can attract digging pests like squirrels.
Depth and Spacing Rules
Planting depth is determined by the size of the bulb. A general rule is to plant the bulb at a depth two to three times its vertical height. This depth helps regulate the bulb’s temperature and provides anchoring for the flower stems.
Larger bulbs, such as daffodils, require deeper planting (six to eight inches deep). Smaller bulbs, like crocus, are planted more shallowly (two to three inches deep). Planting too shallowly can cause the bulb to dry out or be heaved out of the ground by freezing and thawing cycles.
Adequate spacing prevents overcrowding and reduced flowering. Place bulbs three to six inches apart, ensuring they do not touch. After planting, gently refill and firm the soil to remove air pockets. An initial watering will help settle the soil and begin root growth.
Handling Non-Standard Bulbs
Not all underground storage structures are true bulbs; many common garden plants grow from corms, tubers, or rhizomes, each requiring a different planting technique.
Corms
Corms (e.g., crocus and gladiolus) are solid stem tissue, not layered scales. They are planted with the flatter side facing down and the pointed growing bud facing up.
Tubers
Tubers (e.g., dahlias and tuberous begonias) are thickened underground stems lacking a protective outer layer. They are planted with their “eyes” (small growth buds) facing upward toward the soil surface. The tuber is positioned shallowly, just below the soil line.
Rhizomes
Rhizomes (e.g., bearded iris) are horizontal stems that grow at or just beneath the soil surface. These should be planted horizontally, with the top slightly exposed or barely covered with soil.