The best time for the show is in May and June. Then the garden explodes in pink, lavender, white, yellow, blue or deep purple shades. Some of the alliums are quite small while others can be seen from a long distance. No matter their height, they always bring a touch of universal perfection as they reflect the ideal shape: the globe.
If you have a nice free spot (or spots) in your garden where the soil is well-drained, not necessarily rich in nutrients (although it is quite OK if it is) and the spot is exposed to full sun than you might consider planting some bulbs of ornamental onions. I recommend all of them. Of course the number of cultivars is big enough to make my recommendation impossible to realise but you can always try to do your best. Dwarf onions could be grown in rock gardens, tall-growing varieties look great scattered across the garden alone or in groups of three, five or ...pick the number.
The bulbs should be planted in holes three times as deep as the diameter of the bulbs. The ornamental onions can be left in the same location for many years, ideally, undisturbed. Then they will form nice and colorful clusters. The leaves usually wither soon after blooming and do not look too attractive, so they need to be masked with other plants, e.g.: annuals. But do not discard the dry flower heads and especially those of Allium schubertii (vide: Cosmic Garlic published on this blog in June), as they are great for indoor arrangements.