Some people like to pinch off the cotyledons after the true leaves emerge, reports Green Harvest. Unless those leaves are in the way, however, it is best to allow the seedling to decide when it is done with them, or you may accidentally break its stem instead.

When should I pinch back seedlings?

Once seedlings are 3 or 4 inches tall with a good supply of true leaves, I pinch them back. You can use scissors or pruning shears, but thumb and forefinger work just fine. While your seedlings are growing indoors, toughen them up by man-handling them a bit.

When should I start pinching my plants?

Here's how to pinch (or tip) properly: Once your young plant has formed a few pairs of leaves on a stem, it is ready to be pinched. Plants grow buds at the base of each leaf, just above the point where the leaf connects to the stem.