Pruning and topping: what the tree bodies tell owners
The International Society of Arboriculture and the Arboricultural Association publish leaflets for tree owners on pruning, timing and topping. This page reports what they say and where they point an owner who is unsure.
This page is for tree owners. It reports what the named sources say and is not advice about your tree: for that, ask a qualified arborist or one of the offices under Who to call.
Checked against the sources at the bottom of this page on October 9, 2026. Rules, fees and pay change: the source has the last word.
This page reports what the official source says. It is not legal advice: ask the office named here. It is not training and does not teach the work. It reports leaflets written for owners, and it does not say whether any tree needs pruning. The same leaflets send owners to a qualified arborist, and the guides on chainsaw tickets and certifications by country list the courses and credentials that teach the work.
The Arboricultural Association leaflet says trees may be legally protected and that unauthorised work can lead to prosecution. The guide on tree protection laws lists the offices that handle permits.
Why trees are pruned, as the leaflets put it
The ISA Trees Are Good page on pruning your trees calls pruning the most common tree maintenance procedure. It says it must be done with an understanding of tree biology, because improper pruning can create lasting damage or shorten a tree's life, and that each cut can change the way the tree grows. It lists common reasons: removing dead branches to improve form and safety, letting light and air reach plants below the crown, and corrective or preventative work. It describes four types: cleaning, raising, reduction and thinning, and says young trees are pruned to build structure.
The Arboricultural Association leaflet Guide to Tree Pruning lists reasons that include improving structure, removing dangerous or defective branches, reducing shade or wind loading, and giving clearance from a structure. It says removing too big a branch can let disease in through the wound or reduce a tree's vitality because so much leaf is lost. It lists four questions to ask before a branch comes off, among them whether the cut leaves a large wound and whether it removes a large area of leaf. It says removing branches can be dangerous work and that the safest option, particularly for a branch that cannot be reached from the ground, is a trained and insured arborist.
When to prune, side by side
| Point | ISA Trees Are Good | Arboricultural Association |
|---|---|---|
| General timing | ISA says light, routine removal of weak, dead or diseased limbs has little effect on the tree whatever the season, and that wounds close and growth is best when cutting comes ahead of the spring flush of growth. | The leaflet gives late spring through summer, once new leaves have opened and firmed up. |
| Heavy pruning | ISA advises against taking off a lot of living growth right after the spring flush, and says this matters most for weak trees. | The leaflet says to prune as little as possible unless a hazardous defect has to be dealt with, because losing much wood and leaf cuts the tree's food production and stresses it. |
| Species named | ISA notes that diseases such as oak wilt can enter through pruning wounds, and says susceptible trees should be left alone while the disease is actively spreading. | The leaflet says birch, walnut and maples bleed sap in early spring and gives summer or midwinter for them. It gives summer for cherry and other Prunus, which it says partly rely on resin or gum to defend wounds. |
| Periods to miss | Not published on the page. | The leaflet names times when freshly exposed wood would meet drought, frost or the autumn release of fungal spores. |
| If unsure | Points owners to a local arborist. | Points owners to an ARB Approved Contractor or AA Registered Consultant. |
The Arboricultural Association leaflet also holds a table of the best time to prune and the tolerance to hard pruning for many species found in the United Kingdom and Northern Ireland, rated good, fair or poor.
What the sources say about the cut
The Arboricultural Association leaflet says the British Standard for tree work, BS 3998:2010, states that the diameter of the final cut should not exceed one third of that of the parent branch or stem, and describes the branch bark ridge and branch collar as the marks the final cut is placed against. The ISA topping brochure says correct pruning cuts are made just beyond the branch collar, because a healthy tree is equipped to close such a wound if it is not too large. Both texts are written for owners to understand what an arborist is doing. The guide on pruning standards by country describes the standards behind them.
What topping is and what ISA says about it
The ISA brochure Why Topping Hurts Trees defines topping as the indiscriminate cutting of branches to stubs or to lateral branches too small to take over the leader role. It lists other names for it: heading, tipping, hat-racking and rounding over. It calls it "perhaps the most harmful tree pruning practice known" and says it is not a viable method of height reduction and may increase risk in the long term. The brochure sets out reasons in six headings.
- Stress: it says topping can remove 50 to 100 percent of the leaf-bearing crown, and that a tree without enough stored energy may be seriously weakened or die.
- Sunburn: it says suddenly exposed branches and trunk can suffer sunburn, cankers and bark splitting.
- Decay: it says cuts between lateral branches leave stubs and wounds the tree may not close, and few trees can wall off the decay from several large wounds.
- Risk: it says the shoots that follow a topping cut are anchored in the outer layers of the parent branch, can grow as much as 6 m (20 feet) in a year in some species, and are prone to breaking in wind or ice.
- Appearance: it says a topped tree cannot fully regain its natural form.
- Cost: it lists later maintenance, reduced property value and liability, and says damage from a topped tree's failing branch may lead to a finding of negligence.
For alternatives, the ISA leaflets say small branches can be removed back to their point of origin, and larger limbs shortened back to a lateral branch at least one third the diameter of the stem removed, called reduction. They add that sometimes the answer is removing the tree and planting a more suitable species. The ISA pruning page says to consult a local arborist about alternatives to topping.
Palms
The ISA pruning page says most palm pruning removes dead or dying fronds and fruit clusters that could injure people, such as coconuts, and that climbing spikes should not be used on palms because wounds on palms do not close.
Who to call
- ISA Find an Arborist: the ISA directory of arborists, which its brochures point owners to
- Arboricultural Association, find a professional: the directories of ARB Approved Contractors and AA Registered Consultants
- Tree protection offices: the offices that handle permits for work on protected trees
- Hiring an arborist: what the trade bodies say to look for