When planting butternut squash, it’s best to sow the seeds where you want the plant to grow for the duration of the growing season. Squash plants won’t tolerate having their roots disturbed. If you try and transplant seedlings, you’re asking for trouble. Butternut squash should be planted no earlier than 2 weeks after the last expected frost in your area. They can be planted up until 12 weeks or so before the first expected frost in the fall. It’s possible to grow two butternut squash crops in a single year in warmer climates. The seeds germinate best when the soil temperatures are around 65 degrees F. Some folks with limited space wait to plant butternut squash after early spring crops such as lettuce and peas have finished. This is a good way to maximize garden space.
Source: Backyard Vegetable Gardening