Question: My favorite summer-flowering bulb is Allium giganteum. I plant new bulbs every fall, following cultural directions exactly. The first season they produce healthy foliage and perfect flowering stalks. The second year they put out sparse foliage and have no flowers. I live in Zone 4 and wonder if I should consider this bulb an annual in my area.
Answer: Allium giganteum, originally from the Himalayas, is hardy in Zones 4 through 9, so you need not consider it an annual. But you do need to think about its cultural wants. Your bulbs are not storing enough food and energy for the next season. This allium does best in half-to all-day sun and requires a well-drained soil, particularly during the summer. The bulbs should be planted about five inches deep. Plants should also be fed twice a season with an all-purpose fertilizer (5-10-10 granular, a small handful per bulb) when new growth emerges in the spring, and again after the flowers have faded but before the leaves yellow. Like those of daffodils, the bulbs may become crowded in four or five years, requiring lifting and replanting; do this only after the foliage has died down.