Normally my grape hyacinth only puts out leaves in the spring, but this year they all are vigorously growing leaves in the fall. Why do they do that? Is it diagnostic of a problem?
The leaves of Armenian grape hyacinth (Muscari armeniacum) normally emerge in the fall. This species includes many of the modern named varieties. Common grape hyacinth (Muscari botryoides) consistantly sends up leaves in the fall in Washington State, but does this less often in other areas, like Minnesota.
Once grape hyacinths go dormant in the late spring or summer, they require a cold period before they will bloom again. However, for these two species, it appears that the foliage is not so encumbered. If the weather in late summer or fall is sufficiently mild and moist, and the plant is well established, the bulb will send up a tuft of foliage, which will attempt to last through the winter. If the leaves get killed off, it is of no great concern. The plant will send up more with the flowers in the spring.