Should You Prune Hydrangeas in Fall? No — Here’s Why

Take Stock

First things first… Step back and assess how your plants fared this season. With the change in our climate, it is not unexpected that we will need to move some plants around. I personally have to do that with 2 of my big-leaf hydrangeas. Between losing some shade trees in storms and the warming climate, they are just cooking!

Transplant

A non-flowering hydrangea is another reason to make a change. Maybe it needs a more protected place, or maybe it’s time to replace it. In that case, dig it up and donate it to your local town: library, house of worship, community center, etc. If your local garden club has an annual plant sale, they may want it for their next event.

Plants not in protected locations will need a little help if the flower buds are to have their best chance of making it through the coming winter. It’s a hard lesson we learned this past season, as many plants were killed to the ground. Use the off-season to shop around for a replacement hydrangea that will thrive in your now open spot.

For cold climate gardeners, consider moving your non-flowering plant to a protected spot. But do it now. It needs time to establish roots before the ground freezes (at least 6 weeks before your first frost date). If you can plant something nearby that has winter-persistent foliage, such as an azalea, rhododendron, or conifer, do it now. That plant will shield your hydrangea from winter’s wrath. Just watch out for future root competition for water and nutrients.

The Science You Need to Know

Big-leaf (H. macrophylla) or Mountain (H. serrata) Hydrangea

If your plant is a big-leaf (H. macrophylla) or mountain (H. serrata) hydrangea, let the buds form for next year. That means leaving it alone and outside for at least 6-8 weeks after nighttime temperatures are consistently 60 degrees or below. It may even drop all its foliage, at which time you can safely assume it is now asleep. The foliage drop is your signal that the plant has gone completely dormant.

If you fool around with your plants too late in the season, you risk distracting them from 2 important tasks.

1. Bud set, as previously discussed. In late August, we are on the cusp of those cooler nights (thank heavens!), so bud set is right around the corner.
2. What your plants need to do now is settle down to go into a dormant state. For gardeners, that means no additional stimulation.

So, if you prune, fertilize, etc., at the end of August and later, you will be doing the opposite and encouraging them to grow. They will put their energy into developing new growth (which might not survive their coming dormant period), and you will distract them from their main job of setting up next year’s flowers before they enter their rest period.

BOTTOM LINE: NO Pruning or Fertilizing in Fall

What you can do now is finish up any miscellaneous cutting you need to do. I am very cautious about deadheading this late in the season. On rebloomers, those spent flowers serve a useful purpose as umbrellas to protect sleeping flower buds in the stems over the winter. They can also be interesting focal points in your winter garden as they catch the ice and snow.

Remove dead stems

Feel free to cut out any dead stems that have developed during the season for one reason or another. They are very easy to spot now and will make your spring cleanup much easier.

Cutting flowers for bouquets

Go ahead and cut flowers for bouquets. But do it soon. That cutting will stimulate your plant, which you don’t want to do once the conditions are right for bud set. Then it is time to lock up the pruners!