Allium "Globemaster" is a hybrid varietal of giant allium or ornamental onion. Globemaster produces the largest flower heads of any allium, with the diameter ranging between that of a regulation softball and that of a volleyball. The perfectly round purple flower heads sit atop a tall, slim, green stem that reaches up to 3 feet in height. Globemaster flowers from early summer into fall, and the blooms make for dramatic cut flowers that can be opulent or modernly spare.
Select a planting location with nutrient-rich and well-drained soil that receives direct sun for at least 6 hours each day. Loosen the bed's soil to a depth of 10 inches using a cultivating fork or spade, and amend with compost if the soil looks anemic and needs more nutrients.
Plant a Globemaster allium bulb 6 to 8 inches down in the soil with the root plate facing directly down and the slightly sloped end facing up toward the sun. Cover the bulb with the displaced soil and press down lightly. Plant additional bulbs at intervals of 5 to 12 inches.
Water your Globemaster bulbs deeply at planting. Keep the soil lightly and evenly moist at all times, never allowing it to dry out.
Feed your ornamental alliums with a granular bulb fertilizer formula twice a year, with the first application in early spring and the second in late summer or early fall. Water the fertilized area deeply after each feeding.