Growth Habit: Think: garden lollipop. In early spring, 2-3 flat, strappy leaves will emerge from the soil and remain close to the ground. By late spring, a single hollow flower stalk (scape) will emerge, with a papery tip. The spherical cluster of flowers will emerge when the scape is fully erect, though the foliage may already have started to yellow and die back.
Staking: Allium are remarkably strong for their height, but if you live in an area with high winds, it is wise to stake individual flowers.
Watering: Evenly-moist soil is preferred during the growing season. During the dormant season, bulbs can rot if too much moisture is in the soil.
Fertilizing: A small handful of bone meal placed in the soil at planting time is a good idea for root development. After a season in your garden, mulch with compost or well-rotted manure each year for added trace nutrients and improved soil.
Mulching: Allium doesn’t require mulching, but mulching for moisture retention, nutrients and aesthetics is perfectly okay.
Trimming & Pruning: You can remove the flower clusters either when fresh or dry, but it is crucial to leave the foliage intact, allowing it to yellow and die back naturally. Many gardeners leave the flower heads in place through the autumn as they have an almost architectural appearance.
Allium: End of Season Care
If you’ve already tidied up the foliage after die back and cut off the flower scapes, there is no need to do anything more than wait for spring!
Dividing & Transplanting: Allium do not need to be dug and divided.
Pests & Disease: Insect pests are few and far between when it comes to the genus allium. Moles can dig tunnels under the roots, creating air gaps that will dry out and damage the bulb. Mice, voles and gophers will eat allium if there aren’t tulips and crocus to keep them busy.
Additional Concerns: Some species seed prolifically or create tiny bulbils in the flower head that become tiny plants. It is a good idea to check into the specific variety you are buying to make sure that this isn’t an issue.