When to Prune Hydrangeas: A Step-by-Step Guide

Learning about when to prune hydrangeas first requires an understanding of the different types of hydrangeas. Mophead and lace cap blooms occur on older wood. Panicle and smooth hydrangeas bloom on new wood. If you prune your hydrangeas at the wrong time, you may not see any blooms for a year or longer. It's all about timing.

Spring pruning works for new wood hydrangeas (panicle types) such as barre and tree hydrangeas should be pruned back by one-third in March for better strong stems, and to encourage aggressive growth. For older wood types (mopheads), please consider waiting until July when the flowers are spent, and any possible missed buds won't bloom next year.

When it comes to the quality of your hydrangea, soil, method of pruning, and seasonal care are essentials. If you prune too early in the spring, frost will damage the tender buds. If you wait until later in the summer, you may end up removing next year's flowers. You will want to make your cuts about the plant's active growth cycle; it will determine the color of your garden.

Old wood hydrangeas such as mopheads require pruning after blooming, in July or August. If you prune too late, you risk cutting the buds for next year's blooms. The new wood varieties such as panicle hydrangeas will have late winter pruning done in March, encouraging growth in the spring season. You will need to use the shears that correspond to your blooms.

Climate conditions in your area can vary your pruning window. In Zones 4-5, I would encourage you to hold off on pruning until late April to keep growth alive and reduce frost damage. In Zones 9-10, I recommend starting late winter pruning between the first and second week in February. Do summer deadheading cutting spent blooms to keep rebloomers like Endless Summer on bloom into late fall.

Preparing for the fall season involves protecting plants rather than pruning them. After the first frost, feel free to remove dead or diseased wood from your shrubs. Also, add mulch to the bases of plants to insulate the roots. Pruning or trimming shrubs too early can lead to dormant buds being exposed to winterkill. I've observed my neighbors lose whole blooms by pruning their hydrangeas in October.

Old wood bloomers such as Bigleaf and Oakleaf hydrangeas produce buds on stems from the previous year. These need to be pruned directly after summer blooms fall away (this would typically be in July). If you wait until spring, you will lose the summer blooms altogether. I once lost an entire year's blooms by pruning a mophead hydrangea for a client too late.

*New species of wood*, for example, Panicle hydrangeas, benefit from being pruned in late winter at which point they can be trimmed back a third in March to help promote sturdiness. In contrast, smooth hydrangeas benefit most from a hard prune with their stems trimmed to 12 inches, which allows them to strengthen their stems. Lastly, gardeners sometimes overlook, which is soil pH is at least 6.5, which will produce a pink bloom for Bigleaf.

Certain hybrids, such as Endless Summer that rebloom do violate this concept. They will bloom on both old wood and new wood. In the summer, just be sure you deadhead the spent blooms, but do not touch healthy buds. You can do a little spring shaping and still have some fall blooms. I have seen these hybrids bloom until frost with neither pruning nor deadheading if you practice selective pruning.

The bud development stages are very important since they indicate when to prune hydrangeas. The old wood varieties will create flower buds for the following year in late summer. These varieties should be pruned after July, otherwise, you will unnecessarily cut off next season's blooms. Hydrangeas that bloom on new wood, like panicle hydrangeas, will create their buds during the growth of that season, so it is safe to prune them in late winter. The timing is not negotiable.

You are correct that observing the distinction does matter. Old wood hydrangeas, such as oakleaf varieties, will show visible plump buds along last year's stems by fall. New wood varieties will not show any signs of buds until they grow in the spring. I once worked on a bigleaf hydrangea for my client and thought it wouldn't hurt to prune in early April, but it didn't bloom for two years, which was remarkable!

Frost can catch you off guard if you don't pay enough attention to your old wood buds. One fall or spring freeze at less than 25°F will cause flowers that have not developed to die. A simple step is to protect your plants with burlap in growing zones 5-6. Reblooming hydrangeas, such as Endless Summer, hedge their bets by blooming on both old and new wood. To help trigger a second flush of blooms, deadhead the spent blooms.

In the spring, always check plants for winter damage. You can scratch the stems with your thumbnail. If you see green tissue, the plant is still alive. Brown, brittle wood is not alive and you will remove it to the base. This technique saved three hydrangeas in my garden this year after a major frost knocked off all the buds at the top of their stems, and I thought ended their season.

Bypass pruners can center cut through live stems and allow a clean cut for the health of the plant, as if you are using scissors. Anvil pruners will crush dead wood with a blade hitting a flat surface. It is best to use a bypass tool for green growth or softwood up to ¾ inch thick. But anvil types will hold their shape and can be used for dry branches, and are also easy to use without damaging the other plant tissue. So it will be important to choose the correct pruner.

An 8-inch (20 cm) blade offers the best of both worlds: accuracy and strength. This size suits smaller hands and slips into tight places between stems well. I've found this size best for the dense canopy of hydrangeas. Keep the blades sharp; dull tools tear stems, allowing disease to enter. Sharpen your blades about once a month during the height of the season.

After each plant, sterilize tools by either dipping blades into 70% alcohol for 30 seconds or spraying with a 10% bleach solution. Be sure to rinse the bleach tools to avoid corrosion. Last summer, I was able to stop a fungal outbreak by cleaning my shears between gardens of different clients. An ounce of prevention is better than a pound of cure.

Loppers will cut branches that are up to two inches thick. To prune thicker limbs, you will need a pruning saw. Remember to oil trim points weekly for razor-sharp slicing. Store your tools dry until used next to prevent rust. My saw includes a sheath that protects its teeth (and my hands) while it is being transported.

Begin with sanitizing tools using 70% alcohol to avoid disease dissemination or exposure. Wear gloves (the thicker the better) as well as safety glasses and be aware that the sap (from hydrangea) can be a skin irritant, something I learned the hard way after pruning for a few hours leaving my fingers red and swollen for days. Be sure to use clean cuts, they will heal faster.

Distinguishing dead wood begins with scratching the stems with a thumbnail. If you see green tissue beneath the stem surface, the wood is alive. If you see brown, brittle stems, those get cut off at the base of the plant. Dormant wood can often look gray, but it will have some degree of elasticity. Example: Last spring, a client almost removed a thriving oak leaf hydrangea due to mistaking dormant stems for dead stems.

Create thinning cuts above outward-facing buds, at an angle of 45°. This promotes growth outwards from the center of the plant, improving airflow. I mark cut points with a carpenter pencil before cutting. Angled cuts facilitate water shedding and help minimize the chances of rot.

Remove any branches that are crossing or rubbing against other branches. Start with any stems that are growing inwards. For dense plants, I recommend trimming away at least one-third of last season's old wood each year. Last year, this technique revitalized a client's overgrown panicle hydrangea and resulted in three times the number of blooms. Airflow is just as important as sunlight!

The secret to success in all varieties of hydrangeas is timing. Cut back old wood varieties too late, and you will lose next year's crop. New wood varieties need to be pruned back early in the spring so that all of the energy can go into new growth. One miscalculation can set your flowering back 1-2 seasons at least. All you need is a calendar, and that's half the battle!

Inadequate pruning dangers stretch beyond simply losing flowers. Crowded stems will allow pests to get established. Ripped cuts will spread disease. I have rehabilitated gardens where badly infected plants had limited pruning where the customer used the shears that were not sterilized and whole hydrangea clusters suffered the consequences. See the seasonal care guide to avoid these pitfalls. As it is a time of year, are your tools as important as the timing?

Bloom optimization begins with identifying the type of hydrangea and the zone in which it exists. The key is to prune for the timing of hydrangea growth and relax and enjoy the show as flowers appear. For plant health, do not prune more than 25% of the growth in a single season. This will allow the plant to retain energy for continued growth of roots and buds for next year's blooms.

During the autumn season last year, a client pruned her oakleaf hydrangea in September, only to experience a complete failure to bloom in the spring of this year. We reset with the tool guide and planting calendar, and this year's growth has been plentiful. You just need to trust the process. Your hydrangeas will repay your attention to detail with several seasons of color. Now go ahead and grab the sanitized shears.