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Timing and method are essential when it comes to pruning hydrangeas, and they differ depending on the species being pruned. If done improperly, you may prune off next year’s flower buds or cause your shrubs undue stress. On the other hand, making the right cuts at the right time will help keep them looking great and flowering to perfection.
The right techniques and tools are key to good pruning. Here are the basics.
For small branch cuts (up to 1 cm thickness), choose a quality set of sharp bypass pruners (avoid anvil pruners, which dull quickly). Bypass pruners are easy to sharpen and long lasting, if you choose a high-performing brand (I like Felcos). For larger branches (up to 4.5 cm thickness), choose sharp bypass loppers. More powerful pruning tools may be needed for large panicle hydrangeas that become tree-like. For larger cuts, opt for a small, sharp pull-stroke pruning saw to cut through tough branches in no time!
Making the right cuts to branches will facilitate good plant health. Cuts to small branches should be made 2/3 cm from the adjacent stem. Make them at 45-degree angles. Larger branches should be cut flush to the trunk collar. The collar is the ripple of bark that will slowly and protectively grow over the cut. Cuts made above the collar will not heal properly, leaving plants vulnerable to pests and disease.
Prune to the desired height, but beware of over pruning. Refrain from pruning over 1/3 of the top growth, especially in smaller shrubs with well-branched woody top growth. Some species, such as smooth hydrangea (Hydrangea arborescens), are clump forming with stems that can be harshly pruned back, if the clumps are well established and have become overgrown. Others, like panicle hydrangea (Hydrangea paniculata), can become tree like and require more selective pruning.
Hydrangea pruning time is species specific. Follow the following guide for the top four garden hydrangeas.
Latin Name: Hydrangea macrophylla
Best Time to Prune: These hydrangeas bloom on second-year wood, so the best time to prune is in midsummer, just after they bloom. If you prune in later summer or fall, you will cut off next year’s flower heads. Deadwood is common, especially in spring. Dead or dying stems can be removed at any time of year. Old blooms can also be removed at any time, as long as you just remove the flowers and not the buds that have developed below them.
How to Prune: These hydrangeas can grow too large or develop ungainly stems that have grown too high. Shape plants by cutting wayward or old stems to the ground. Stems can also be trimmed to a desired height, depending on the density of the overall shrub. Refrain from shearing bigleaf hydrangeas if you want to maintain a more naturalistic, appealing appearance.
Comments: Bigleaf hydrangeas can have either lacecap (Hydrangea macrophylla var. normalis) or mophead flower clusters. Lacecaps have a looser more naturalistic horizontal growth habit and should be pruned less formally. Mopheads tend to have a rounder habit better suited to uniform pruning. In northern zones above USDA Hardiness Zone 6, these shrubs may die to the ground, so they will never flower. Protecting the crowns with Fafard Premium Natural and Organic Compost and straw can help protect their flowering stems from winter cold.
Latin Name: Hydrangea quercifolia
Best Time to Prune: Oakleaf hydrangeas also bloom on second-year wood and should be pruned just after blooming in midsummer. Once shrubs have leafed out in spring, identify and remove any dead wood from the previous year.
How to Prune: Some compact oakleaf hydrangeas have rounder, tidier habits but most reach 8-feet in height and develop a broad, naturalistic habit. Remove overgrown or crossing branches. If they overgrow an area, shrubs can be hard-pruned back by half in midsummer. Just be sure to leave plenty of green leafy branches for strong growth, and keep newly pruned shrubs irrigated through dry summer days to encourage new growth and bud set.
Comments: The pretty flower panicles of oakleaf hydrangea dry nicely and look good in winter gardens. Remove the old blooms in late winter to keep shrubs looking fresh in spring.
Latin Name: Hydrangea paniculata
Best Time to Prune: These tall, hardy hydrangeas bloom on new wood, so the best time to prune is in late winter or early spring. Remove ungainly or crossing branches and dead wood at this time. Refrain from summer pruning, and avoid removing more than 1/3 of the top growth at pruning time.
How to Prune: Panicle hydrangeas are variable shrubs that tend to be tall (8-15 feet) and bushy or tree-like, but some cultivars are compact for small-space gardens. Selectively prune bushy varieties, cutting tall branches to the trunk or base of the plant. Cut the large branches of tree-like varieties to the trunk, making sure cuts are flush to the collar.
Comments: These shrubs revive quickly from pruning. Tree-form plants may develop suckers from the base of the trunk. Keep these pruned off to maintain a single trunk. The dry blooms of panicle hydrangea also look good through winter but should be removed in spring.
Latin Name: Hydrangea arborescens
Best Time to Prune: These easy-to-grow hydrangeas also bloom on new wood and are best pruned in late winter or early spring. They respond well to harsh pruning and can even be pruned to the ground if they outgrow a space. By late spring, they will have grown back with vigor. Refrain from summer pruning.
How to Prune: Pruned these bushy shrubs uniformly to keep their habit rounded. Large-headed varieties, like Incrediball™, are top heavy and appreciate regular pruning to 1/3 height to keep stems shorter and sturdier. Refrain from pruning large-headed varieties to the ground.
Comments: The bushy dry flower heads look great in winter but should be removed by spring. These hydrangea root very easily from cuttings. Take any pruned branches, dip them in rooting hormone, stick them in the ground, and keep them evenly moist. They will root in no time!
Putting your garden to bed properly will result in a prettier, healthier garden this season and next. It’s essential to know what areas to clean, what to prune, what to leave undisturbed, and what to protect over winter. Simply taking a leaf blower to your beds and landscape is a start, but there’s more to the process, if you want to do it right.
Cleaning, Cutting, and Edging
When cleaning your garden beds, consider bed appearance, but also consider plant appearance and health. This means determining what should be cut back and cleaned and what should be left alone until spring.
Begin by cleaning out loose leaf material by hand or blower with a focus on the most visually conspicuous areas. Smart gardeners are wise to leave some leaf litter in beds to provide added winter protection for more tender plants and help support overwintering pollinators. (Some species of overwintering native bees, and butterflies use undisturbed leaf litter as essential winter habitat. Click here to learn more.) After clearing away unwanted leaves, give your fading garden plants needed attention.
Dead or dying annuals are the first thing to cut back or pull. If some have mature seed heads, consider scattering their seeds in hopes of getting a few self-starters in spring. Once annuals are removed and beds smoothed, start work on your perennials and shrubs.
Many perennials look great over winter and their crowns are protected by leaving the top growth intact through winter. Most ornamental grasses, lavenders, hardy salvias, hardy chrysanthemums, and rosemary are perennials that should not be cut back until spring. Exceptionally hardy perennials that die to the ground, such as daylilies, coneflowers, hardy geraniums, hostas, Shasta daisies, and asters, can all be fully cut back without worry. Some perennials produce seed heads that naturally feed overwintering songbirds, such coneflowers, asters, and hardy sunflowers, so it is nice to leave a few up. All healthy evergreen perennials and shrubs should be left alone.
Keep it Covered!
After cleaning and cutting back beds, cut fresh bed edges, and apply cosmetic mulch. [Click here to read more about garden edging.] Lots of mulches will work, but dark, earthy leaf mulch is like landscape gold. Not only does it look good, but it breaks down quickly to naturally feed soil, and it is easy to create from recycled leaves. [Click here to learn how to turn your fall leaves into leaf mulch.] Screened, partially composted bark mulch is another good option for broadcast mulching. For small garden spaces, Fafard Premium Natural & Organic Compost should be applied as a high-quality, fortifying mulch.
When mulching, work around perennials and shrubs. Many plants will die or perform poorly if their crowns and trunks are thickly layered with mulch. Succulents, alpine or rock garden plants, and Heuchera should never have heavy mulch applied on or around their crowns.
In fall, start by cutting back any dead, unhealthy, or crossing branches from trees and small shrubs. When pruning out dead, diseased, or infested wood, prune just below the point where growth is still fresh and healthy. If you think that a plant you are pruning is diseased, be sure to clean your pruning shears in a 10% bleach solution before pruning another plant. If additional pruning on flowering trees and shrubs is needed to shape the plants, first determine whether your shrubs bloom on old or new wood. It is okay to prune new-wood bloomers in fall but not old-wood bloomers.
French lilacs (Syringa vulgaris), azaleas and rhododendrons (Rhododendron spp.), forsythia, most viburnum, service berries (Amelanchier spp.), and some hydrangeas, such as oakleaf hydrangea (Hydrangea quercifolia) all bloom on old wood—meaning they set their flower buds for the next year shortly after they bloom. These plants should never be pruned in fall, unless you want to cut off all of next year’s flowers. Old- or second-year wood bloomers are best pruned right after they flower. Hybrid roses (Rosa spp.), buddleja, crepe myrtle (Lagerstroemia indica), and some hydrangeas, such as wild hydrangea (Hydrangea arborescens), bloom on new wood, so fall pruning is an option.
Pruning techniques vary from plant to plant. As a general rule, shrubs that bloom on new wood are forgiving and can be hard pruned, or cut back nearly to the ground. In fact, hard pruning is often recommended for sprawling, aggressive bloomers like Buddleja. Rose pruning is another beast entirely and most recommended for late winter. [Click here to learn more about rose pruning.]
Toss it or Compost It?
Bed cleaning creates lots of waste. Some of the waste is perfect for composting and some is best discarded. Loose leaf matter makes great compost. Fall grass clippings and leftover edging pieces can also be thrown into the compost heap. Old perennial and annual waste can also be composted, if it appears to be clean and disease free. Healthy woody branches can also be chipped and added to the bin. Any material thought to have pests or disease should be thrown away. This is especially the case for vegetable waste, such as last-season’s tomatoes, which commonly develop early and late blights. Rose clippings should also be kept far away from the bin because of the many diseases these plants can harbor. [Click here to learn more about rose diseases and pests.]
Clean, coiffed beds, with crisp edges look great and will make spring prep a breeze. They will also make it easier to plan and implement fall bulb plantings and decorate for the winter holidays.