Last Fall I planted a row of young yew to form a low decorative hedge. The hedge to be 15” high by 15” wide. Can you advise when to trim, and how much at a time to trim, along with any other advice. Thank you
Yew Hedges are among the most forgiving hedges there are and will excuse most mistakes. You do need to clip or prune yew hedge plants to make them bushy – shortening side branches causes them to produce the twiggy growths that help make a yew hedge be dense and elegant.
Pruning Yew hedges immediately after planting:
On planting (October-March) cut back any side growths that straggle so you leave the line of yew hedge plants looking reasonably straight sided. You should leave the branches at the bottom of the plant just a little longer than the ones near the top so your hedge has slightly sloping sides. For the time being do not cut the top of the plant off. The growing point of a yew hedge plant is vigorous and can grow up to 40 cms in a season. This helps your yew hedge increase in height rapidly. Once cut off the plant never regains the same vigour again.
Pruning Yew hedges in later years:
Yew hedges are best trimmed in late winter or early spring – just before the first flush of growth in the spring. In the early years, the more often you clip the side branches, the bushier your yew hedge will become. I recommend gently clipping in April, July and October for the first couple of years at least (always leaving the growing point alone, of course). Remember to keep forming the hedge to a tapered shape with the top narrower than the bottom to allow light to get to the lower branches.
When your yew hedge has reached the height you want (let it grow about 10 cms higher than you think you want) you can cut the growing points off. Reduce the height little by little as if you take too much off, you may be waiting a year or two for it to grow back.
Thereafter, just clip when your yew looks like it needs a trim. No hedge is more forgiving of pruning mistakes than the yew. This is because yews will sprout new growth from old wood.
Yews can become very tall hedges if allowed to grow. Pruning them so they remain 15″ by 15″ seems extremely small. As they respond well to pruning, I assume it is possible. It will be important to cut off the growing tip when it reaches 20″ and then you can slowly lower the hedge to it’s desired height.
This article has a small bit of information on formative pruning of yew hedges. Their advice is the same as mine. Don’t cut growing tips on top (leaders) just yet and snip straggly side shoots. https://www.rhs.org.uk/plants/types/hedges/pruning-guide
Here is an article on the Basic pruning principles of woody plants.