“Flower globes” refer to the ornamental members of the Allium genus, commonly known as ornamental onions. These plants are characterized by spherical flower heads perched atop tall stems. The globe-like blooms, which are dense clusters of numerous tiny florets, create a bold, architectural presence in any garden setting. Ranging from compact varieties to towering forms that can exceed four feet, alliums provide a unique structural element among lower-growing perennials. This distinct shape and height make them a focal point in the landscape.
Selecting the Site and Planting Instructions
Selecting a site that provides full sun exposure is important. While these plants can tolerate partial shade, maximum flowering and stem strength are achieved with direct sunlight. Drainage is paramount for bulb health. Heavy clay soil must be amended with organic matter like compost and grit or sand to prevent water from sitting around the bulbs, which can lead to rot.
Planting should occur in the fall, between September and December, allowing the bulbs time to establish roots before the ground freezes. Plant the bulb two to three times its height, ensuring the pointed end faces upward. For larger varieties, this means planting them at least six inches deep. Spacing depends on the size of the bulb; large globe-forming varieties require at least eight inches of space for good air circulation, while smaller bulbs can be planted a few inches apart.
Seasonal Watering and Feeding Regimens
During the active growth phase in late winter and spring, the soil should be kept moist to support the foliage and flower stalks. Allium bulbs are susceptible to rot, so allow the top layer of soil to dry between watering sessions. Once the flowers fade and the foliage starts to yellow, watering must be reduced significantly, as the plants are entering their rest period and dislike summer irrigation.
Fertilization is generally unnecessary in rich soil, but a light application of fertilizer in early spring is beneficial on average soils. A low-nitrogen, high-potassium formula, or bulb-specific feed, is ideal. The low nitrogen content prevents floppy foliage growth at the expense of the bloom. Taller varieties, such as Allium giganteum, can develop weak stems or flop over in windy conditions. Discreet staking should be done early in the season before the stems become too heavy, which helps maintain the plant’s upright form.
Managing Spent Blooms and Dormancy
Once the flowers have finished their display, deadheading prevents the plant from expending energy on seed production. This energy is redirected back into the bulb, ensuring a robust flower display the following year. However, leaving the dried seed heads intact provides sculptural interest and texture through the late summer and even into winter.
The management of the foliage is the most important step for ensuring perennial return; the leaves must be left untouched until they have withered and turned yellow or brown. This process allows the leaves to photosynthesize and transfer energy reserves back down to the bulb for next season’s bloom. Prematurely cutting the green foliage will weaken the bulb and may result in a lack of flowers the subsequent year. When the foliage is dormant, the withered material can be cut back to ground level.
Allium bulbs should be lifted and divided only when clumps become overcrowded or when flower production begins to decline, which typically occurs every three to five years. Division is best performed in the fall when the plant is fully dormant. The crowded bulbs are dug up, separated, and then replanted at the correct depth and spacing in fresh soil.