Pruning and Plant Maintenance

Plant Pruning and Maintenance

Chapter Introduction

Pruning and plant maintenance are core skills of the landscape horticulturist trade. Beyond the aesthetic aspect, pruning influences plant health, safety, flowering, fruiting, and longevity. This chapter covers the physiological principles, techniques, tools, timing of interventions, safety rules, and applicable Canadian standards. You must master these concepts to pass the Red Seal exam, as questions focus as much on the "why" as on the "how."

Physiological Principles of Pruning

Apical Dominance and Plant Hormones

Plant growth is regulated by hormones, primarily auxins, produced at the terminal bud. These auxins inhibit the growth of lateral buds, a phenomenon called apical dominance. When you prune the terminal bud, the auxin concentration decreases, and lateral buds develop. Understanding this mechanism is essential for predicting a plant's response to a cut.

Light pruning: moderately stimulates lateral growth.

Severe pruning: triggers vigorous growth of many buds, sometimes at the expense of flowering.

Thinning cut: removes entire branches at their point of origin, which reduces the number of buds without excessively stimulating regrowth.

Sap Flow and Wound Healing

Raw sap rises through the xylem (roots to leaves), and elaborated sap circulates through the phloem (leaves to roots). A poorly placed cut can interrupt these flows. Wound healing occurs through the formation of callus tissue (covering tissue) from the cambium. A clean cut, without tearing, promotes rapid healing and reduces the risk of fungal infection.

Root-to-Shoot Ratio

Above-ground pruning reduces leaf surface area, and therefore photosynthesis, which temporarily affects the root system. Conversely, root pruning (during transplanting) must be compensated by a proportional above-ground prune to avoid water stress. The general rule: the more roots you remove, the more you must prune the crown.

Types of Pruning and Objectives

Formative Pruning

Performed on young trees and shrubs to structure the framework. Objectives:

Establish a dominant central leader (for trees with a pyramidal habit).

Remove crossing, weak, or narrow-angle branches.

Space scaffold branches evenly (generally 15 to 30 cm vertically).

Maintenance Pruning

Maintains shape and vigour. It includes:

Removing dead, diseased, or broken branches.

Removing water sprouts (vigorous vertical shoots) and suckers (shoots arising from roots).

Reducing density to improve light penetration and air circulation.

Fruiting Pruning

Applied to fruit trees to maximize production. Principles:

Encourage fruiting wood (spurs, short twigs) and remove excessively vegetative growth.

Open the centre of the tree (open-centre form) for light.

Balance the fruit load to prevent branch breakage.

Rejuvenation Pruning

Used on neglected or overgrown shrubs. It involves cutting old stems back to ground level (coppicing) or severely reducing them. Caution: not all plants tolerate this type of pruning. Conifers, for example, do not regrow from old wood.

Safety Pruning and Tree Trimming

Aims to remove hazardous branches (near power lines, buildings, public roadways). In Canada, trimming near power lines is strictly regulated. Only certified arborists may work near energized conductors, and minimum distances must be respected (see Standards section).

Pruning Timing

The timing of pruning depends on the species, climate, and objective. Here is a reference table:

Type of Plant	Recommended Time	Reason
Deciduous trees (maple, oak, linden)	Late winter / early spring (before bud break)	Dormant sap, rapid healing, structure visible
Spring-flowering trees (lilac, magnolia)	Immediately after flowering	Avoids removing the current year's flower buds
Summer-flowering trees (panicled hydrangea, spirea)	Late winter or early spring	Flowering occurs on the current year's wood
Conifers (pine, spruce, fir)	Late spring / early summer (candle growth)	Regrowth is limited; prune during active growth
Berry shrubs (currant, raspberry)	Late winter	Stimulates production of new fruiting canes
Heavy-sap trees (birch, sugar maple)	Late summer / early autumn	Reduces sap flow (bleeding)

Golden rule: never prune during periods of intense frost (below -10 °C) as the wood becomes brittle and cuts risk splitting. Also avoid pruning during severe drought.

Cutting Techniques

The Collar Cut (or Flush Cut)

Cut the branch just beyond the branch collar (the swelling at the base of the branch), without damaging it. This zone contains specialized cells that promote wound healing. Never cut flush against the trunk (flush cut) as this damages the trunk and opens a large wound.

The Reduction Cut

Shorten a branch back to a lateral bud oriented in the desired direction. The cut should be angled, at approximately 45°, 5-10 mm above the bud, with the top of the cut sloping outward to prevent water accumulation.

The Three-Cut Technique (for Heavy Branches)

To prevent bark tearing, proceed in three steps:

49.First cut: 30-45 cm from the trunk, from underneath, one-third of the way through the diameter.

50.Second cut: from the top, 5-10 cm further out than the first cut, to sever the branch.

51.Third cut: at the branch collar to remove the remaining stub.

Coppicing

Cutting all stems of a shrub to 10-15 cm above the ground. Used for willows, dogwoods, elders, and certain maples. To be done in early spring.

Tools and Equipment

Hand Pruners

Anvil pruners: a sharp blade strikes against a flat anvil. Suitable for dead or dry wood, but crushes living tissue. To be avoided for precision cuts.

Bypass pruners: the blade passes in front of a counter-blade. Clean cut, ideal for living wood. To be preferred.

Loppers (Long-Handled Pruners)

For branches 2 to 5 cm in diameter. Offer increased leverage. Ratchet models multiply force.

Pruning Saws

Hand saw: curved blade, three-sided teeth, cuts on the pull stroke.

Pole saw: for high branches, up to 4-5 m.

Chainsaw: reserved for branches over 10 cm in diameter. Requires training and full protective equipment.

Hedge Trimmers

Manual: for low hedges and finishing work.

Electric or battery-powered: for medium-sized hedges.

Gas-powered: for large hedges; more powerful but heavier and noisier.

Personal Protective Equipment (PPE)

Mandatory according to CSA standards:

Safety helmet with face shield (CSA Z94.1).

Safety glasses (CSA Z94.3).

Hearing protection (CSA Z94.2) if noise levels exceed 85 dB(A).

Cut-resistant gloves (ANSI/ISEA 138 standard).

Steel-toe boots (CSA Z195).

Chaps or cut-resistant pants for chainsaw use (CSA Z611 standard).

Canadian Standards and Regulations

Trimming Near Power Lines

The Canadian Electrical Code, Chapter V (C22.5) governs work near power lines. Minimum working distances are defined according to voltage:

Line Voltage	Minimum Distance (workers and non-insulated tools)
0 to 750 V	3 m
750 V to 75 kV	3 m + 10 mm per kV above 750 V
75 kV to 250 kV	4.5 m
250 kV and above	6 m

Practical rule: if a branch is within 3 m of a line, you must contact the electrical utility. Never attempt to prune it yourself. Wet trees or conductive metal tools significantly increase the risk of electrocution.

CSA Standards for Equipment

CSA B149.1: Natural Gas and Propane Installation Code. Applies indirectly if you work near gas vents or meters. Maintain a minimum clearance of 1 m around dryer vents and 0.5 m around gas meters.

CSA Z133: Safety standard for arboricultural operations. It covers work methods, equipment, safety distances, and required training for arborists.

Green Waste Management

Pruning residues must be managed according to municipal regulations. Composting is encouraged. Diseased branches (e.g., fire blight, verticillium wilt) must be burned or sent to a landfill, never composted, to prevent the spread of pathogens.

Calculations and Practical Measurements

Estimating Waste Volume

To estimate the volume of wood chips or residues after pruning, use the formula for the volume of a conical pile:

V = (π × r² × h) / 3

Where:

V = volume (m³)

r = radius of the base (m)

h = height of the pile (m)

π ≈ 3.1416

Example: A pile of branches has a radius of 1.5 m and a height of 1.2 m.

V = (3.1416 × 1.5² × 1.2) / 3 = (3.1416 × 2.25 × 1.2) / 3 = 8.482 / 3 = 2.83 m³

Dosing Wound Sealants

The use of wound sealants (pruning paint) is discouraged on healthy cuts; natural healing is preferable. If you apply a product to a wound (e.g., oak during wilt season), follow the manufacturer's instructions. Most products are applied in a 2-3 mm layer, without overflowing onto the bark.

Calculating Leaf Surface Area After Pruning

To balance root and shoot pruning during transplanting, it is estimated that the crown should be reduced by 20 to 30% to compensate for root loss. If you transplant a tree with a trunk diameter of 10 cm, the root ball should have a diameter of approximately 60-80 cm (6 to 8 times the trunk diameter). The above-ground prune should then be proportional.

Diseases, Pests, and Sanitary Pruning

Sanitary Pruning

Consists of removing infected or infested parts. Rules:

Disinfect tools between each cut on a diseased plant (70% alcohol solution or 10% bleach solution).

Cut 15-20 cm below the visibly infected area.

Burn or dispose of diseased tissue; do not compost it.

Common Diseases Related to Pruning

Disease	Causal Agent	Symptoms	Pruning Measure
Fire blight	Erwinia amylovora	Scorched flowers and shoots curling like a shepherd's crook	Cut 30 cm below the lesion, disinfect tools
Verticillium wilt	Verticillium spp.	One-sided wilting, brown discoloration of vessels	Remove affected branches, avoid excessive pruning
Cytospora canker	Cytospora spp.	Sunken areas, gum exudation	Cut below the canker, improve air circulation
Root rot	Armillaria, Phytophthora	General decline, fungi at the base	Reduce the crown to compensate for root loss

Pests and Pruning

Aphids: pruning infested shoot tips can reduce the population, but be careful not to stimulate tender regrowth that will attract more aphids.

Leaf miners: mined leaves must be removed and destroyed.

Scale insects: heavily infested branches must be cut and disposed of.

Species-Specific Pruning

Ornamental Trees

Maple: light pruning in late winter. Avoid large cuts in summer (risk of leaf scorch).

Oak: prune in winter (November to March) to prevent the spread of oak wilt (Ceratocystis fagacearum), transmitted by insects attracted to fresh sap.

Birch: prune in late summer to avoid spring sap "bleeding."

Shrubs

Bigleaf hydrangea (Hydrangea macrophylla): only prune dead stems in spring. Flowering occurs on the previous year's wood.

Panicled hydrangea (Hydrangea paniculata): prune severely in early spring (to 30-60 cm from the ground) for abundant flowering on the current year's wood.

Vanhoutte spirea (Spiraea vanhouttei): prune after spring flowering to maintain a compact shape.

Hedges

Formal hedge: prune 2 to 3 times per season. The base must be wider than the top (trapezoidal shape) so that light reaches the lower branches.

Informal hedge: light pruning after flowering, without cutting into the main framework branches.

Conifers

Pine: pinch the candles (new shoots) by hand in spring to densify. Never cut into old wood.

Spruce and fir: prune new growth in June, before it hardens.

Juniper: light pruning in summer, never into old wood.

Common Mistakes and Their Consequences

Mistake	Consequence
Flush cut (at the trunk)	Large wound, slow healing, risk of rot
Cut too far from the bud	Stub dries out and becomes an entry point for pathogens
Pruning during frost	Wood cracks, tissue death
Excessive pruning (more than 30% of the crown)	Water stress, dieback, loss of vigour
Trimming near power lines without authorization	Risk of electrocution, fines, civil liability
Failure to disinfect tools between diseased plants	Spread of diseases
Pruning conifers into old wood	Permanent bare patches

Pitfalls to Avoid

139.Confusing formative pruning and fruiting pruning: the former structures the framework, the latter maximizes fruit production. The objectives and cuts differ.

140.Pruning all plants at the same time: spring-flowering plants (lilac, forsythia) must be pruned after flowering, not in spring.

141.Forgetting tool disinfection: during sanitary pruning, every cut on a diseased plant must be followed by disinfection. A single oversight can contaminate an entire tree.

142.Underestimating electrical safety distances: the 3 m distance is an absolute minimum. Always verify the line voltage before starting.

143.Using anvil pruners on living wood: they crush tissue, which delays healing and promotes infection.

144.Pruning more than 30% of the crown at once: this causes physiological shock. If severe pruning is necessary, spread it over 2-3 seasons.

145.Neglecting the trapezoidal shape of hedges: a hedge that is narrower at the base loses its lower branches and becomes bare.

146.Believing wound sealant is always beneficial: on healthy cuts, it can trap moisture and promote rot. Use it only on large-diameter wounds (> 10 cm) or in cases of specific disease.

147.Pruning roots without compensating with a crown prune: during transplanting, the root-to-shoot imbalance causes severe water stress.

148.Ignoring municipal regulations on burning residues: some municipalities prohibit burning. Always check local regulations.

Summary

Pruning is based on understanding apical dominance and plant hormones (auxins).

The main types of pruning are: formative, maintenance, fruiting, rejuvenation, safety.

The pruning time depends on the species and flowering season. As a general rule: prune deciduous trees in late winter, spring-flowering plants after flowering, and conifers during active growth.

Cuts must be clean, angled, 5-10 mm above a bud, and respect the branch collar.

The three-cut technique is mandatory for heavy branches to prevent bark tearing.

Tools must be adapted to branch diameter: hand pruners (up to 2 cm), loppers (2-5 cm), saw (5-10 cm), chainsaw (over 10 cm).

Personal protective equipment is mandatory: helmet, glasses, gloves, boots, hearing protection.

The Canadian Electrical Code, Chapter V imposes minimum distances of 3 m near low-voltage power lines.

Sanitary pruning requires rigorous tool disinfection and cutting 15-30 cm below the infected area.

Never exceed 30% crown reduction in a single intervention.

Pruning mistakes are often irreversible: caution and knowledge of species are your best allies.

Self-Assessment Questions

164.Why should you not prune a lilac in spring?

165.What is the difference between a collar cut and a reduction cut?

166.What minimum distance must be maintained near a 25 kV power line?

167.What is the role of auxins in apical dominance?

168.Why should the base of a hedge be wider than the top?

169.What are the three cuts in the heavy branch pruning technique?

170.When should you prune an oak in Canada and why?

171.What is the volume of a branch pile with a radius of 2 m and a height of 1.5 m?

172.What PPE is mandatory for chainsaw use?

173.Why should you not apply wound sealant to a healthy cut?

Normative References

Canadian Electrical Code, Chapter V (C22.5) — Work near power lines.

CSA Z133 — Safety standard for arboricultural operations.

CSA Z94.1 — Protective headwear.

CSA Z94.3 — Eye and face protectors.

CSA Z94.2 — Hearing protectors.

CSA Z195 — Protective footwear.

CSA B149.1 — Natural Gas and Propane Installation Code (clearances around vents and meters).

This chapter provides you with the essential knowledge to approach exam questions on plant pruning and maintenance. Carefully review the tables and safety rules, as they are a frequent source of questions. Good luck with your preparation!