Tulips and hyacinths are perennials and many people prefer to leave their bulbs in the ground and avoid digging them up. However, the flowers in both plants tend to be short-lived when propagated in this manner. It is preferred that the bulbs be dug up, dried and stored for the winter (see Reference 1). The correct time to dig up bulbs is after the foliage has completely died back and not before. The most important reason for this is that the foliage supplies the bulb with the energy it needs for the next season's growth and flowers (see Reference 2).
Digging up Hyacinth and Tulip Bulbs
Spring bulbs like tulips and hyacinth should be dug and stored for the winter unless the winter temperature is cold enough to allow for complete dormancy in the ground. The bulbs need at least 15 weeks of cool temperatures of 40 to 50 degrees Fahrenheit during the winter (see Resource 1).
It is important for the foliage on bulbs, as well as of rhizomes, tubers, and corms, to have died completely before the bulbs are dug up. If the bulbs are pulled up before the foliage has naturally yellowed, the bulb is deprived of its critical food supply and this affects next season's growth. Although digging up and storing bulbs is not an easy chore, it has many advantages such as increasing the number of plants and having the choice to replant the flowers in another spot in the garden in spring (see Reference 2). Tulip and hyacinth bulbs are also very delicate, so it is advisable to remove them by early summer, store, and replant again the following fall (see Reference 3).
Approximate Time for Foliage Yellowing
The better conditions are for the bulb before its removal, the better it will perform the following season. And the best of all conditions is to let the foliage yellow naturally and completely before removal. After the flowers on the bulbs have gone completely, it takes at least four extra weeks of photosynthesis from the foliage to the bulb to support the coming year's flowers. Many gardeners find the dying foliage an eyesore in their garden. But it is necessary and should not be disturbed. A couple of remedies for this are to let the grass around the flowers grow long so that it covers the unattractiveness or the yellowing foliage can be tied together to give a neater appearance (see Reference 3).