We're at that awkward time of year – the shrubby hydrangeas are looking really tatty, and at the same time are bursting into life, but it's too early to prune them properly, as we are certain to have a few more frosts before the month is out.
So what is the best thing to do?
My answer is to do a partial prune, right now: this is a technique I have developed over the years, which satisfies Clients who are sick and tired of looking at dead brown flowers, but which does not place the plant at risk.
The risk, in case you didn't know, is that if you prune a Hydrangea “properly” and then we get a hard frost, the frost can damage the new buds. You then have to remove those frost-damaged buds, and this can leave you with a mis-shapen, or drastically smaller-than-required plant.
My partial prune consists of removing the horrible tatty brown flower heads from last year, but rather than cutting the plant back to the traditional “pair of nice fat buds”, I merely take off a few inches of stalk: often I will simply take off roughly the same amount all the way round, leaving a neat shape.
If there is time, I lean inside the plant and remove any stems which are obviously quite dead: such stems are usually pale grey-white, and don't have any sign of buds whatsoever, and as soon as you cut them, you can tell that they are dead. If you are not quite sure whether a stem is dead or not, take off just an inch or two and look at the cut end: if it is hard, brown and dry, the stem is dead, but if it is soft and white or green in the middle, then it is still alive and there is hope for it yet.
I usually also take the opportunity to remove any weak and spindly stems, any misplaced ones, any that are growing too low to the ground, and any that are shooting off in the wrong direction, and spoiling the outline of the plant.
Opening up the centre of the plant in this way allows air, light and rainwater in, which has the dual benefit of encouraging new growth, while discouraging bugs and diseases – what I call a win-win! - and also making it easier for me to do the proper prune in a few weeks' time, when all risk of frost is past.
If, however, you are a bit nervous about damaging your Hydrangeas, then just take off the dead flowers, and do the thinning when you do the main post-frost prune: I tend to do it now because I think it prevents the plant wasting energy on stems that are going to be removed in a few weeks' time anyway, not to mention the fact that it looks neater, but it won't do the plant any harm if you don't do it now.
I've attached two photos of a large Hydrangea halfway through the process, one photo from each side: as you can see, the overall size of the shrub is reduced by only few inches, leaving plenty of room for a proper prune later on, but it improves the appearance quite dramatically!