Allium Sprouts . Drought, lack of sun and boggy soil can also prevent alliums from flowering. Allium holds its stunning spherical blooms high above the foliage, adding whimsy and drama to your garden. Allium Sepa. Onion Bulb, Green Sprouts On A Black Background Stock from www.dreamstime.com Heights also vary, with some alliums standing just 5 inches tall, and others reaching 4 feet. Starting allium seeds is easy. Carl linnaeus first described the genus allium in 1753.