Once squash plants get going, they can produce a bounty. If your butternut squash vine has taken over your garden, trimming it back won't harm the squash crop and can be beneficial. Winter squash plants like butternut produce an average of 20 lbs. of squash . Pruning the plant once you have several baby squash growing won't affect this amount and will free up garden space for other crops.
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Wait for your squash plant to develop flowers and set fruit. There's no need to prune it before this happens.
Identify four to five developing fruits that are spaced evenly on the plant. Leave these to develop into squash.
Use pruning sheers to cut the remaining developing squash from the vine. Discard these.
Clip the growing squash vine two leaf nodes past the young butternut squash. This prevents the plant from continuing to put energy into growth, allowing it to concentrate on growing the squash you left on the vine.