Pinching out tomatoes means that you nip off side shoots, that is, the ones that come in the “armpits” just above the leaves between leaf and stem.

Which ones should be pinched out?
Not all tomato varieties should be pinched out; it is only the tall-growing, ordinary varieties that it should be done on. Bush tomatoes that only reach a few decimetres in height should not be pinched out, since even the side shoots on these will have time to develop fruit. Do, however, remove a few large leaves if they shade the ripening tomato trusses.

How to pinch out tomatoes
Nip off the side shoots on the tomato plants when the shoots have reached about 5 centimetres long. On “potato-leaved” varieties, where the distance between the leaf pairs is greater, you can let the side shoots grow 10–12 centimetres long before you pinch them off. The side shoots help with photosynthesis and shade the plant against too much sun.

Otherwise these side shoots take energy from the ripening tomato trusses and are unnecessary, since there shouldn’t be so many trusses on a plant that it cannot support them. In the worst case the tomato plant may abort the unripe tomatoes.

Also remove the lowest leaves on the tomato plant, especially if they start to look ragged or turn yellow. You can also remove some of the foliage once the tomato plant has finished growing, so that the leaves don’t stop the sun reaching the ripening tomatoes.

If, in the latter part of summer, the tomato plant shoots up in length and becomes thin and lanky at the top, you can nip off the top too, so that the tomatoes that have already set have time to ripen.