When should a thuja hedge be trimmed and how much?
By Service Plus Stockholm ABUpdated 5 min read
Short answer
When during the year should a thuja hedge be trimmed, and how much growth can be removed each time?
A thuja hedge is normally trimmed twice a season, the first time from late May to mid-June and the second time from late August to mid-September. Each time, only the current year's new shoots are removed, never cutting back into the brown wood, since thuja does not sprout new growth from bare branches. Shape trimming is done with a 2–5 cm margin to the intended final size so the hedge has time to fill in green before winter.
Why thuja differs from leafy hedges
Thuja is a conifer and does not behave like privet or hornbeam when it comes to pruning. A leafy hedge can be cut back hard and will sprout new shoots from bare stems, but thuja only carries green growth on its outer branches. If you cut into the brown wood inside the hedge, no new needles will grow back there, leaving a bare gap for several years or permanently.
This makes timing and cutting depth more important for thuja than for most other hedges in the Stockholm area.
Which two times are best for trimming
Thuja hedges are best trimmed twice a season in Stockholm's climate. The first trim is done once the spring growth has developed properly, usually from late May to mid-June. The second trim is done in late summer, from late August to mid-September, before growth slows down ahead of autumn.
- Late May to mid-June, after the spring shoot but before midsummer
- Late August to mid-September, before night frost becomes common
- Avoid trimming in July during extreme heat and drought, as the hedge is already under extra stress then
- Avoid trimming after mid-September, as the shoots won't have time to harden before winter
How much we take off a thuja hedge
Thuja does not shoot again from old, woody growth, which makes every cut into the brown irreversible. Our hedge specialist Tuja trims only in the green outer zone, keeps the hedge slightly narrower at the top than at the base so the light reaches all the way down, and takes a little every year rather than a lot every third.
A hedge that has already grown too wide can rarely be narrowed in one season. Then we spread the work over several years, one side at a time, so the green surface has time to grow back. We bring pole trimmers, scaffolding and a trailer, and the cuttings are hauled away as an option.
What happens if you cut too hard or at the wrong time
Cutting into the bare, brown wood creates bald patches that will not green up again, since thuja lacks dormant buds where the needles have already fallen off. The only solution then is to wait for nearby branches to grow over the gap over time, which can take several seasons, or to remove and replace the affected plants in the row.
Trimming during intense heat or drought also increases the risk of brown, wilted patches, as the hedge is already under stress. Water the hedge a few days before trimming if the summer has been dry.
- Bald patches after hard trimming heal very slowly or not at all
- Replace individual plants if the damage is severe, rather than waiting several years
- Do not trim during intense heat or an ongoing drought
- Water the hedge as needed before trimming in a dry summer
Practical tips for trimming
For an even result, it helps to stretch a guide line along the top and sides of the hedge as a reference, especially for long hedge rows at housing cooperatives (BRF) and joint property associations. Trim the sides with a slight inward slope towards the top, so light reaches the whole hedge and the lower parts don't thin out over time.
- Stretch a guide line as a reference for a straight top and straight sides
- Trim the sides with a slight inward slope towards the top
- Collect and remove the clippings the same day so the hedge isn't smothered from below
- Check the hedge height against the property boundary; see our separate article on permitted height towards neighbours and the street
How Service Plus helps with your thuja hedge
Service Plus Stockholm AB trims thuja hedges for homeowners and under ongoing agreements for housing cooperatives (BRF), joint property associations and property companies across Greater Stockholm. Tuja, our hedge specialist, assesses the hedge's condition and growth on site and plans the trimming so the right amount is removed at the right time without leaving the hedge bare. Get in touch for a free quote before work begins.
Common follow-up questions
Can a thuja hedge be trimmed just once a year?
Yes, that's possible if the hedge already has the desired size and you're happy with a slightly looser shape, but for a dense, even hedge, two trims per season are better since less is removed each time.
Can thuja be trimmed in spring before the new growth appears?
It's possible but gives a worse result, since you'd then be cutting into last year's matured needles instead of soft new growth; it's better to wait until late May or early June.
Why do parts of the thuja hedge turn brown after trimming?
This is usually because the cut went into the brown, needle-less wood that doesn't sprout new growth, or because the hedge was trimmed in intense heat and drought without enough watering beforehand.
How old should a newly planted thuja hedge be before you start trimming it?
Generally wait one season after planting before starting shape trimming, though light topping to encourage dense growth can be done as early as the second summer, depending on the size of the plants at planting.
