When my father taught me how to start plants from seed some 50 years ago, pinching was a very common practice. You used to pinch seedlings when they had 4 to 6 true leaves and it was almost universally applied to annuals and herbs, although rarely to vegetables.
Pinching means removing the terminal bud, the plant’s growing point. When the terminal bud is nixed, this stimulates dormant buds lower down on the plant to spring into action. Usually, each pinch at least doubles the number of stems, giving a much denser and more attractive plant with more leaves (herbs) and more flowers (annuals). It does slow the plant down a bit, but usually within 5 to 7 days, the seedling will be sprouting new growth.
Traditionally, pinching really is done exactly like the term suggests: by pinching the growing point between the thumb and forefinger. Since the bud is still soft, it comes right off. Of course, you can also cut off the bud with scissors or pruning shears… and that is still considered “pinching”.
Pinching is still used on more mature plants (shrubs and houseplants notably) to keep them in check, but pinching seedlings is a bit of a dying art. Most modern varieties of annuals and herbs have been selected to be self-branching. Old-fashioned basils and coleus, for example, used to shoot straight for the sky, but many modern varieties begin producing branches almost as soon as they have true leaves. If your seedlings are producing secondary branches, they won’t need pinching. Likewise if the plant’s label suggest it branches well, is self-branching or “needs no pruning”.
That said, there are still older varieties around… and I’ve never seen a cosmos seedling that couldn’t use a pinch or two.
Here is a list of plants that it may be useful to pinch… but even with these plants, do look before you pinch.
- Sweet Pea