The most ideal time to cut a yew hedge is in early spring, around about March. It will then start shooting again in April. You can easily cut yews right back, down to the old wood — they can tolerate that. After pruning, you would be looking through a hole, however, which is not that attractive in a hedge that is then merely waist-high. The aim must therefore be for the surface of the hedge to fill in quickly and become green again. That can easily take two to three years. But you can speed this up by boosting new growth with 50 grams of composite fertiliser per square metre of hedge. As soon as the shoots are the length of a finger, cut them back by between a third and a half. Do the same after each new growth of the existing shoots; once the new sprouts reach finger length, trim them by the same amount again.
A reduction in the height of the yew hedge also means a change in width! The gardeners' old hedge rule applies here: With every ten-centimetre increase in height, the hedge loses one centimetre in width. Cutting sloping sides enhances the alignment of the hedge to the sun, which reduces the risk of too much balding in the lower part of the hedge. In this way, you also follow the natural pattern of the plant. According to the theory of apical dominance, growth in the upper third of hedge plants is stronger than in the lower third. After changing the height of your yew hedge, you should therefore also adjust the width. For example, if it is 90 cm high and has a width of 70 centimetres at the base, give both sides a sloping cut, so that the upper width of the hedge measures 52 centimetres. Calculation method: 90 centimetres in height means 9 centimetres width reduction on either side of the hedge, making 18 centimetres in total. 70 centimetres base width minus 18 centimetres equals 52 centimetres top width.