I'm in western NY in the US and I have a potted tulip plant. When can I move it to the ground? After the last frost of the season? I usually see planted tulip plants start to pop up in March, bloom before April, and the flowers are gone before May, but these came from the store. I don't want them to die when I plant them.
Wait until the bulb goes dormant (when the top growth withers and dries completely). Remove the bulb from the potting soil completely, and cut the roots off near the basal plate, and cut off the stem/leaves. Plant it right away in good, non compacted garden soil, 8 inches down (make sure there is plenty of good soil below that level as well). No need to water. They will root in during late summer/fall.
If there is more than one bulb, make sure they're spaced 6" or more apart when planted.
It's best done in fall, but any time after last frost is fine.
For best (not necessary, but more fun) results you could start them now in quart containers and transplant after the Spring rains are over.
They're hardier than they're given credit for, so it's nothing to worry too much over. After frost is fine.
Unless I've misunderstood, you appear to be saying you have a tulip bulb planted in a pot - what's not clear is whether its currently in or out of doors. If it was under cover or indoors when you bought it, and you've had it indoors since you got it, and especially if its showing growth, you will have to wait until its flowered, and then transplant into the ground outdoors when the ground isn't frozen. It's important that the foliage is allowed to remain on the plant for six weeks after flowering is over, so if the weather is still very cold outdoors, then you will need to harden it off before planting outside. Fertilize it when the flowers are gone but the leaves are still present. When you turn it out of its pot to place in your prepared hole in the ground, keep the rootball intact so you don't disturb or break the roots, because that would mean the leaves will die. Alternatively, let it remain in its pot, water it but don't keep it wet, fertilize as advised, and plant outdoors once the leaves have started to shrivel, or, better yet, keep it outside in its pot and plant in the ground in October, or earlier if your winter is usually such that the ground freezes in October.
The usual rule for planting bulbs is twice or thrice the depth of the bulb, but tulips often do better in succeeding years if they are planted deeper than that. Some varieties, though, do not grow well again, or do not produce flowers in following years.
If, on the other hand, the pot was outside at the store, and you already have it standing outdoors, then transplant into a prepared hole in the same manner, that is, taking care not to disrupt the rootball, or you'll lose the flowers and leaves, and only if the ground is not frozen or waterlogged.