Shooting up to 6 feet tall, they have gray-green leaves and bear big, round, deep purple flowerheads 5 to 10 inches across. This will assure sturdy stems so flowers will be less likely to flop. Among the last of the perennials to bloom, its flowers often don't open until late September or October. These huge flowers blossom the size of softballs with a gorgeous purple color and sway atop sturdy stems in late spring. Surely the biggest is the aptly called giant onion, A. giganteum. Depending on species and variety, they may grow in U.S. Department of Agriculture plant hardiness zones 3 through 10. Herbaceous alliums (such as Allium tuberosum and Allium Millenium) have fiberous roots like other perennials. They hate waterlogged soil. They should be planted in fall between September and November, before the soil freezes. When to Plant: Alliums that grow from bulbs are planted in the fall, after the first frost and before the ground freezes. No reason why not. Alliums (Allium spp.) Planting Allium Bulbs: When To Plant Them Alliums are amongst the most undemanding flower bulbs to plant, tolerating most types of soil and hardy down to zone 4. Soil type. Soil must be light and drain well, and even poor soil is fine. A good tip to know how deep to plant it is to multiply the height of the bulb by 3. Just make sure the pot is deep and fairly large and the compost is kept moist in the growing season. Allium loves high sun exposure. Giant Allium (Allium giganteum) is the tallest of the large flowering allium with 4"-6" diameter, ball-shaped flowers.The Giant Allium adds a wonderful element to a garden and will even catch the eye of the non-gardeners! Varieties like the star of Persia (allium christophii) and giant allium (allium hollandicum) produce distinctive globe-shaped lilac-purple flowers which make for excellent flower arrangements, both fresh and dried. Ozawa allium (Allium thunbergii 'Ozawa'): A tidy, clump-forming plant that grows 18″ to 20″ high. Alliums are not great grown all by themsleves as their leaves are fading and look relatively unattractive just as the flowers open. The other thing to think about is underplanting. Planting Alliums in Pots and Containers. The large A. giganteum, aka giant allium, grows up to four feet tall with six to eight-inch purple blooms. Planting in the ground. It blooms with eight-inch violet-purple flowers atop 12 to 18-inch stalks. These may be planted at any time during the growing season. Another late-bloomer that flowers in autumn. Allium giganteum is planted in fall more or less 4 to 5 inches (10 to 12 cm) deep in light soil. Planting allium. A. cristophii, commonly known as star of Persia, is the parent of several ornamental allium favorites. If it is 2 inches (5 cm) tall, plant … For the most productive display of blooms, plant alliums in full sun. span a broad range of garden favorites from ornamental bulbs to kitchen-garden essentials most cooks can't be without. Some of the giant varieties can benefit by being planted near a wall or fence for some protection from strong winds, so you won't have to worry about your stunning blooms snapping in a storm. Plant the bulbs at a depth of roughly 3 … The best allium to grow in pots is A. karataviense. Bees love it. Alliums will grow perfectly well in a well-drained soil. As its Latin name says, these are the big guys. Depending on the height of the allium, tall alliums look great at the back of a border and small varieties are well-suited for containers. Alliums are relatively easy to grow from seed, although germination can be lengthy depending on the variety you are planting. 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