, » April 26, 2024

Pruning Perennial Plants: Tools, Tips & Timing

A cedar shrub being pruned with hedge trimmers

When And How Should You Prune Perennial Plants?

Pruning is is essential for all shrubs and evergreens as it promotes new growth and blooms. Properly pruned shrubs will be superior to those that have been neglected, poorly pruned or pruned at the wrong time of year. But, when and how should your plants be pruned? In this blog we’ll explore the best tools and practices for pruning common perennials in Southwestern Ontario; plants that have a lifetime spanning several years in our climate. We’ll touch on specific techniques and timing for common plants that you might find in your own garden beds.

Tools For Pruning

There are many pruning tools available, both hand tools (unpowered) and power tools (battery, plug-in, and gas powered). The selection can be overwhelming for a new gardener just starting to discover their green thumbs, however, most pruning can be completed with a few key tools that every gardener should include in their collection.

A photo of garden pruning tools sitting in a garden
Secateurs (top), Hedge Shears (middle), And Loppers (background)

Secateurs (also known as hand pruners) are used in a single hand, similar to scissors. They are ideal for precision pruning of perennials and flowering shrubs with branches or stems less than 2cm in diameter. There are two types of secateurs; bypass and anvil. Both have a curved upper blade but each has a different style of lower cutting bade. Bypass secateurs have a curved lower cutting blade and both blades move past each other to create clean and precise cuts. By comparison, anvil secateurs don’t have a blade on the bottom, but a wide metal base that the top blade cuts against. They make more of a crushing cut that delivers more power. While most secateurs are hand tools, you can find electrically powered options. These can be helpful for gardeners who have trouble with grip strength or find the handles uncomfortable.

Loppers work like secateurs but on a larger scale, with two long handles that meet at a hinge to provide greater leverage for the curved blades. Some loppers may have handles that extend for even greater force at the blades. Also like secateurs, loppers are available with bypass blades – for cleaner precision cuts, or anvil blades – for more powerful crushing cuts. Loppers are best at removing dead branches from mature shrubs or young trees with limbs around 2cm in diameter.

Serrated blades, or reciprocating saws with wood-rated blades can be used to remove large woody branches greater than 2cm in diameter. A serrated blade on a bow saw, hack saw, or hand saw has teeth that grip and cut neatly through these larger limbs. A reciprocating saw performs the same, only with a powered blade that cuts back and forth at greater speed to help get the job done quickly and with less effort.

Hedge shears or powered hedge trimmers are the best tools for shaping hedges and efficiently cutting down spent growth from grasses and shaping large shrubs. These tools are meant for smaller branches and stems and are used to cut back young growth on shrubs and hedges to keep them shaped, or tender stems on grasses. Hedge shears work like secateurs and loppers, but have two long bypass blades that can cut across multiple branches at the same time. Electric and gas powered hedge trimmers have multiple double edged teeth on a long blade called a cutting bar that reciprocates back and forth to cut any branches the blade comes in contact with.

In addition to the right tools, always be sure to wear the proper safety gear for the equipment you’re using. For power tools, this includes proper hearing protection, eyewear, and footwear. Be aware of your surroundings and people near you. Choose the correct tool for the type of pruning needed and inspect each plant before pruning to ensure there are no loose debris, thicker branches than your tool can handle, or other hazards.

A group of yew shrubs being pruned using a hedge trimmer
A Yew Being Pruned Using Hedge Trimmers

Tool Care

It’s important to keep your tools in good working order. This not only ensures that they last for many years, but remain safe. Proper care also prevents your tools from transferring any unwanted pathogens like bacteria, fungi, and viruses to your plants during pruning. When pruning, you are creating a small area no longer protected by the outer layers of the plant’s epidermis (like getting a shallow cut in your skin. This increases the risks of infection if you are pruning other plants with the same tools, which might be carrying a disease.

  • Clean your tools after each use and make sure they are dry when put away. This will keep them free of debris and prevent rust or corrosion during storage.
  • Sanitize your tools after use, or after each cut when pruning any diseased plants. This prevents pathogens from spreading between branches and plants. You can sanitize your tools using ethanol or isopropyl alcohol by dipping or wiping the blades.
  • Sharpen your blades regularly. Depending on the size of your garden and plants, the timing between sharpening will vary, but you will start to notice as dull blades become ineffective. If you let your tools become too dull, they will no longer make clean cuts, which can be damaging to your plants. Additionally, because dull blades require more force, the extra pressure increases the chances of them slipping, and they actually become more dangerous to use. Sharpening can be done at home with sharpening files, or you can take your tools to a professional sharpening shop.
  • Lubricate moving parts on tools. Prevent your tools seizing by lubricating moving parts like blades, chains, and hinges. Requirements will vary between hand and power tools, be sure to check any manuals for detailed instructions. Most hand tools can be lubricated using multi-purpose oils like mineral oil or WD40, but it doesn’t hurt to check the manufacturer’s specifications.
  • Store your garden tools in a dry place like a tool shed or garage. While most modern hand tools will be made using composite, plastic, and stainless steel parts, some older tools may have wooden handles or metals more prone to corrosion. No matter the materials, it’s always a good idea to keep your tools stored in a dry place. This prevents unnecessary exposure to the elements and extends their lifetime.
  • Keep any blades in the “locked” position when not in use. This is primarily a safety precaution to prevent injuries while tools are stored, moved, or not in use. Keeping any tools with blades exposed can also lead to accidental damages like chipping or denting, especially if dropped or hit by another hard object.
  • Do not service any tools while powered! For gas tools this means that the engine is shut off, and for electric tools this means the motor is no longer supplied by wired or battery power.
A lavender plant being pruned using a hedge trimmer
A Lavender Plant Being Pruned Using Hedge Trimmers

Why Is Pruning Important?

Keeping plants pruned should be part of your regular garden maintenance routine. While most pruning will be done in the spring, there are some fast growing plants which may need to be pruned more than once per season. Selectively pruning dead or diseased wood and stems helps keep your plants healthy. Trimming back branches helps promote new growth by reallocating resources from the root system. You can also prune plants for form, to keep their growth contained to a certain shape (like a box hedge), or even as topiary.

General Rules of Thumb For Pruning

Many common plants used in Southwestern Ontario garden beds can be classified as either herbaceous perennials or woody perennial shrubs which include spring flowering, old wood flowering, summer flowering, and evergreen shrubs.  Pruning techniques will generally be similar between species that fall into each of these categories, however the best timing for pruning often depends on the growing and flowering seasons. We’ll go over how a plant can be classified in one of these categories, and some plants you might recognize from your own garden. While you should always check the specific requirements for your own plants, some general rules of thumb for each type of plant are below.

A lavender plant being pruned using a hedge trimmer
A Cedar Topiary

 

Herbaceous Perennials

Herbaceous plants are leafy and tender, they have stems that grow and then die back each year. They include flowering bulbs, tubers, rhizomes, corms, perennial wildflowers, grasses, and ferns. Plants such as tulips, daffodils, hyacinth, day lilies, and hostas can have their flower stalks cut back when spent and foliage cut down to a little above the ground after it starts to wither and yellow. This allows the bulb time to reabsorb energy from the foliage.  For other plants like cone flowers and grasses some gardeners may choose to cut back spent summer growth in late fall after the growing season, while others may leave it for added winter garden interest. However, following winter, the prior season’s dead growth should be removed from herbaceous perennials by early spring, allowing for new growth to flourish.

Common Herbaceous Perennials
  • Perennial Grasses
  • Ferns
  • Russian Sage
  • Garden Phlox
  • Bulbs: Daffodils, Tulips, Hyacinth, Asiatic Lilies
  • Tubers: Day Lily, Hosta, Dahlia
  • Rhizomes: Bearded Iris, Foam Flower
  • Corms: Crocus, Gladiolus
  • Coneflower
  • Butterfly Weed
  • Salvia
  • Coreopsis
  • Lavender (although old growth is woody)
A group of black-eyed Susan flowers
Black-Eyed Susan Flowers

Woody Perennial Shrubs

A woody plant has stems that live for several years and form stiff structures from which new growth continues to be added every year. Woody plants can include trees, shrubs, or vines. We’ll focus specifically on pruning woody shrubs as tree pruning can require some additional finesse, especially for mature trees. We recommend contacting a professional arborist.

Woody perennial shrubs can be pruned any time during their dormant season, when their form is unobstructed by foliage or flowers. Typically, the ideal time is before new growth begins – either late winter, or early spring. However, for plants that bloom on old wood, which is growth from the previous season, it’s best to prune immediately after flowering or not at all. Generally, woody perennials should be cut back at most by one third of the plant size to encourage new growth. This will allocate resources stored in the roots over winter to the branches remaining after pruning. During pruning, woody perennial shrubs can be shaped up to complement their natural growing form – mounded/round, pyramidal, columnar, or rectangular.

Spring Flowering Shrubs

A spring flowering shrub is a woody perennial that blooms early in the growing season. Shrubs that flower in spring and early summer should be pruned once they have finished flowering to promote vigorous blooms for the next year. The plants listed below flower on new growth in the spring.

Common Spring Flowering Shrubs
  • Azalea
  • Flowering Dogwood
  • Sand Cherry
  • Viburnum
  • Rose Of Sharon
  • Dogwood
  • Barberry*
  • Burning Bush*

*These plants have an inconspicuous bloom, meaning their flowers are not showy and can easily be overlooked or mistaken for foliage.

A row of mature shrubs along a path next to a home showing how the plant growth looks before being pruned
Perennial Shrubs Just Before Being Pruned Showing The Prior Season’s Growth
A row of mature shrubs along a path next to a home that have been neatly pruned
Perennial Shrubs After Pruning And Shaping

 

Summer Flowering Shrubs

Shrubs that flower during summer should be pruned before they begin producing new growth and buds. It’s always best to prune shortly after the shrub has flowered. Avoid waiting to prune too late in the spring when you risk removing active growth and buds. The plants listed below flower on new growth during the summer.

  • Climbing Hydrangea
  • Smooth Hydrangea
  • Big Leaf and Mountain Hydrangea that are rebloomers (flower twice per growing season)
  • Butterfly Bush
  • Shrub Rose
  • Summer Lilac
  • Summer Blooming Spirea
  • Potentilla
  • Smokebush
A close-up of a lilac bloom
Lilac Bloom

Old Wood Blooming Shrubs

Old wood is growth on a woody perennial that is a year or more old, these are branches from the previous growing season. Plants that bloom on old wood form buds on branches in the summer or fall which then flower the following season. It is important to prune these plants at the correct time or you will lose the blooms for the next year. Most old wood blooming shrubs will flower very early in the spring, which is why their energy is spent producing buds before the winter. Spring flowering shrubs that bloom on old wood should be pruned directly after they have finished flowering.

Some species of hydrangea also bloom on old wood. All oakleaf hydrangeas and some big leaf and mountain hydrangeas flower on old wood. They flower later in the season, leaving no time for additional growth after flowering if pruned in the fall. It is best to only prune old wood flowering hydrangeas to remove dead or damaged branches. If you must prune an old wood flowering hydrangea back, do it after the plant’s blooms are spent. Pruning will not harm the plant, but will prevent it from being able to flower the following season.

Old Wood Blooming Shrubs
  • Forsythia
  • Lilac
  • Rhododendron
  • Ninebark
  • Weigela
  • Spring Blooming Spirea
Old Wood Blooming Hydrangeas
  • Oakleaf Hydrangea
  • Big Leaf and Mountain Hydrangea that are not rebloomers (flower once per growing season)
A pink hydrangea flower among green foliage
Big Leaf Hydrangea Bloom

Evergreen Shrubs

Winter burn on evergreen shrubs can be removed in early spring. New growth should be pruned back to half its length in early summer. This will promote dense growth rather than long shoots extending away from the shrub. It’s important with evergreen shrubs not to prune past the existing healthy green growth into the woody growth, especially with species like cedars, as this will create a bare spot in their greenery that will not recover. Yews are the exception to this rule, they can be cut back to old woody growth and will recover.

  • Boxwood
  • Juniper
  • Cedar
  • Yew
  • Euonymus
  • Dwarf Spruce
  • Dwarf Pine
  • Holly
  • Arborvitae
  • False Cypress
  • Cotoneaster
A group of yew shrubs that have been pruned into mounded forms
A Grouping Of Recently Pruned Yew Shrubs

 

Remember, Timing Is Key

The most important thing about pruning is to time it correctly for the types of plants in your garden. Make sure you’re familiar with your garden and are pruning to facilitate the health, growth, and best blooms from your plants through all seasons. Use the correct tools for the job and keep them in good working condition. Ensure that dead and damaged branches are removed when noticed, while seasonal pruning is completed at the right times to avoid removing buds before they flower. Don’t prune evergreens too aggressively, follow the natural shape of the plant, or shape of your topiary. Most of all, enjoy your time in the garden and the results of your efforts!

Want to learn more about your plants or expand your garden? Check out the Connon Nurseries Plant Finder: https://app.connon.ca/

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