How do I know if my tulip bulbs are dead? How long do they keep green leaves before withering each year?

A Tulip's Lifecycle

By now, your tulips are hopefully resting happily underground, waiting for next Spring to arrive.

After a tulip flowers, the fleshy green leaves convert sunlight to energy through photosynthesis and stores the energy in the bulb. It will probably take several weeks for the leaves to turn brown depending on how hot it is and how much rain you get. Then the tulip bulb begins a long dormant phase underground waiting for the ground to cool and moisten again and the cycle repeats.

It can't hurt to fertilize the planting area in the Fall. A little food can never hurt.

If you remember where you planted the tulips and are really concerned about them coming back next year, you can always dig up a couple and check to see if they're still there and if they're healthy and firm like an onion in the grocery store.