How to Grow and Care for Alliums: Super Tips
Many people overlook the beauty of onions as plants, but there are related species of plants that are truly deserving of a spot in your flower garden. These plants, known as fast-growing ornamental alliums, are the perfect choice when it comes to grow and care for alliums. They possess tall stems with rounded flower heads that consist of numerous star-shaped flowers. Although these alliums are not meant for consumption, their leaves emit a subtle onion-like fragrance when they are crushed.
While ornamental alliums may not enhance your culinary endeavors, they can certainly add vibrancy and charm to your garden. These plants are incredibly resilient, as they are able to withstand challenging conditions such as drought and cold weather. If you’re looking to grow and care for alliums, here are a few tips. Furthermore, when it comes to grow and care for alliums, these plants are not bothered by common garden nuisances like deer and rodents. With a wide range of allium varieties available, specifically selected for their resilience and beauty, you can easily find the perfect ones to suit your garden’s needs. It is important to note that for successful growth and establishment, allium bulbs should be planted during the autumn season.
Botanical Name: Allium
Common Name: Ornamental Allium
Mature Size: 1-4 feet tall, 3-10 inches wide
Sun Exposure: Full sun
Soil Type: All; must be well-draining
Soil pH: 5.5-6.5
Bloom Tim: Spring, but there are fall bloomers
Plant Type: Bulb or rhizome
Flower Color: Pink, purple, yellow, white, and green
Hardiness Zones: 4-10 (USDA)
Native Area: Middle East
Toxicity: Mildly toxic to humans, toxic to dogs and cats
How to Care
Although the majority of alliums are plants that develop bulbs, there is a small group that grows from rhizomes, similar to common chives (Allium schoenoprasum). These particular alliums may never produce any type of bulb. The leaves of allium plants are typically long and slender in shape. Some varieties, such as the cork-screw allium, maintain their attractiveness throughout the entire season, displaying a blue-green color that complements their flowers. However, most early blooming alliums have foliage that tends to wither and die back early, as the plants enter a dormant phase during the summer.
Allium flowers are formed in clusters and are most commonly recognized for their rounded pom-pom shape. However, they can also take on star-shaped, cup-shaped, semi-circular, or pendulous forms. There is a notable diversity in the appearance of allium plants. For instance, drumstick alliums only reach a height of about one foot and feature 1-inch flower heads, whereas the giant ‘Globemaster’ variety can grow up to 4 feet tall and showcase enormous globes with flower heads measuring 8 to 10 inches in diameter.
The majority of allium bulbs exhibit rapid growth, resulting in their blooming during the spring or early summer, typically after the initial spring bulbs have faded away. Nevertheless, there exist a few varieties that showcase their blooms later in the season, extending well into the fall.
The delightful, plump, and round shape of allium flowers adds a charming touch as they emerge amidst other plants. Whether nestled among low-growing mats like hardy geraniums or alongside shrubby roses, they create an appealing visual display. Their purple color serves as a valuable asset, harmonizing well with a wide range of late spring flowers, including peonies, irises, and catmint. Additionally, the shape of the allium flowers complements medium-height plants such as foxgloves or monarda.
One significant drawback of early-blooming alliums is the tendency for their leaves to deteriorate even before the plants reach their flowering stage. If possible, it is advisable to conceal the foliage by positioning a denser plant in front of them. Daylilies, for example, work effectively for this purpose, providing a natural screen for the declining allium leaves.
Light
To ensure optimal flowering and robust growth of your allium plants, it is recommended to select a location that receives abundant sunlight throughout the entire day. While alliums can tolerate partial shade, it is advisable to provide them with as much sun exposure as possible, considering that many of these plants have relatively short blooming seasons.
Soil
Alliums have a preference for soil with a slightly acidic pH level, typically ranging from 5.5 to 6.5. However, it is crucial to prioritize the soil’s drainage quality over its pH. It is essential to avoid allowing the allium bulbs to remain in damp soil, especially during their dormant period, as prolonged moisture can lead to rotting. To promote adequate drainage while ensuring sufficient water reaches the bulbs, incorporating a generous quantity of organic matter into the soil prior to planting is highly recommended. This addition of organic matter helps enhance the soil’s ability to drain effectively while maintaining an appropriate level of moisture for the bulbs.
Water
Alliums require infrequent watering, and if there is regular rainfall, it typically fulfills their watering needs. However, in the absence of sufficient rain, watering the alliums every three to five days is adequate.
Climate and Moisture Level
The hardiness of allium plants relies on both the specific variety being cultivated and the prevailing growing conditions. However, the majority of allium species thrive within a broad range of USDA hardiness zones, specifically zones 4 to 10. It is important to note that different allium varieties may exhibit varying degrees of tolerance to different climate conditions, so it is advisable to research and select the appropriate allium varieties that are best suited for the specific hardiness zone in which they will be grown.
Fertilizer
If you regularly improve the quality of your soil through amendments, it is possible that you may not require additional feeding for your allium plants. However, in cases where the soil conditions are less than optimal, applying a small amount of balanced fertilizer as the plants begin to develop flowers can be beneficial. This fertilizer application helps replenish the energy reserves that the allium plants utilize during the blooming process. By providing the necessary nutrients, the plants are supported in producing healthy and vibrant flowers.
Types of Allium
Drumstick allium: (Allium Sphaerocephalon) these alliums feature clusters of 1-inch flowers that bloom in early summer, starting off with a greenish hue and gradually resembling red clover. For the best visual effect, it is recommended to allow them to freely wander throughout the garden, pleasantly surprising you as they peek out amidst other flowers.
Corkscrew allium: (Allium senescens ssp. montanum var. glaucum) the distinctive characteristic of this allium variety lies in its blue-green leaves, which twist and turn, giving it its common name. Due to its growth from rhizomes instead of bulbs, you may find it categorized within the perennial section of garden centers. In mid- to late summer, it showcases flattened ball-shaped lavender flower heads measuring 2 inches in diameter.
Globemaster: The flower stalks of Globemaster alliums are impressively tall, reaching heights of 3 to 4 feet, and are crowned with enormous ball-shaped flowers spanning 8 to 10 inches in diameter. Another noteworthy tall allium is Mount Everest, which, although slightly smaller than Globemaster, boasts creamy white blooms.
Japanese onion: (Allium thunbergii) This variety presents charming 1-inch pink flower heads that bloom in early fall, resembling more of a mop-like appearance rather than a round globe. Notable cultivars include Ozawa, which features larger purple flower heads, and Alba, known for its white cup-shaped florets. Unlike other alliums, Japanese onion grows from rhizomes rather than bulbs and can often be found in containers.
Nodding onion: (Allium cernuum) This allium variety produces gracefully drooping clusters of flowers in delightful shades of pink and purple. The flower stems typically reach an average height of 2 to 3 feet. Nodding onion is highly adaptable and can thrive even in partial shade.
Purple Sensation: The flower stalks of Purple Sensation alliums grow to approximately 2 feet tall, topped with vibrant purple flowers forming a 2- to 4-inch globe. While Purple Sensation bulbs tend to be long-lasting, the leaves tend to yellow or turn brown quite early, which can slightly diminish the overall visual appeal compared to the stunning flowers.
How to Prune
Alliums do not exhibit the ability to bloom more than once during a given growing season. Once the flowers have completed their bloom cycle, it is recommended to trim down the flower stalks. This pruning action redirects the plant’s energy towards storing nutrients and vitality within the bulb for future growth. However, it is worth noting that the dried flower heads of alliums possess their own aesthetic appeal, and numerous gardeners choose to retain them in their upright position. This decision adds an additional visual element to the garden, as the dried flower heads continue to provide interest and charm even after the live flowers have faded.
How to Propagate
To successfully grow bulb-forming alliums, it is recommended to plant them in the autumn season. The depth at which they should be planted should be two to three times the diameter of the bulbs. For instance, if you have a 2-inch bulb, it should be planted at a depth of 4 to 6 inches. After planting, ensure that they are watered thoroughly, and then patiently await the arrival of spring.
It is important to note that bulb-forming alliums have a slow rate of multiplication. However, over time, they will begin to produce small offsets either on the original bulbs or possibly even on the flower head. Once the plants have finished flowering, you have the option to lift the bulbs and remove these offsets. The offsets can be replanted immediately, although it may take a couple of years before they reach the flowering stage.
As for the rhizome-forming alliums, they can be planted at any time. It is worth mentioning that the fall-blooming varieties may not be readily available at the garden center until late summer. Rhizome-forming alliums can be lifted and divided whenever the clump starts to appear crowded. It is advisable not to wait until the center of the plant begins to die out before considering division.
Common Pests and Diseases
Similar to their culinary relatives, ornamental onions do not typically attract a significant number of pests. They are generally avoided by deer and rodents.
While ornamental onions can be susceptible to certain fungal diseases such as downy mildew and rot, these issues are less prevalent in a flower border compared to a vegetable garden. To address this, it is recommended to avoid overhead watering and promptly remove any infected bulbs.
When it comes to insect pests, it is advisable to be cautious of snails, slugs, and the allium leaf miner. However, since the foliage of ornamental onions does not persist for a long time, any cosmetic damage to the leaves is generally not a cause for major concern.
