Alliums, thanks to their roots as native plants, are exceptionally tolerant of both cold winters and hot summers. These plants require very little in the way of winter care. After they've bloomed, you may choose to deadhead your allium plants-however, allow them to retain their foliage until it dies back naturally. The tall stems of allium add plenty of summertime interest to your garden, and the leaves allow the plants to continue to store energy for the upcoming season.