The evergreen thuja (arborvitae) is a classic choice for garden hedges. Discover the best time for thuja trimming as well as care and maintenance tips.
17.01.2025
Gentle shaping is always permitted, but radical cutting back of your thuja is prohibited between March and September to protect nesting birds – what’s more, trimming at that time would also ruin your hedge. The exact regulations can be found in Section 39(5) of the German Federal Nature Conservation Act (Bundesnaturschutzgesetz, BNatSchG).
Thuja hedges should be trimmed between the beginning of April and September. The best time for trimming thuja hedges is in June, and fast-growing varieties should also be trimmed again in August. An exception to this rule is if birds are breeding in the hedge; in this case, pruning is prohibited. Radical pruning is also prohibited between March and September under Section 39(5) of the Federal Nature Conservation Act (BNatSchG). You should also avoid pruning thuja hedge in strong sunshine or when the hedge is wet.
How often you should trim your thuja depends on the plant’s age and growth. A young thuja should be trimmed twice a year after the first year to encourage rapid, dense growth, while an older thuja only needs trimming once a year. For thuja topiary, trimming three times a year is best to keep it in shape.
The height to which you should trim your thuja depends on its location. In many German municipalities, hedges may not be allowed to grow more than two metres tall. It is therefore best to find out directly from your municipality or city whether there are any regulations concerning hedge height.
You shouldn't cut your thuja back hard, as it won't regrow afterwards. It is better to regularly trim your thuja into shape. You should also bear in mind that, under the Federal Nature Conservation Act, it is prohibited to cut hedges back to the trunk between March and September.
Yes, you can cut off the brown parts of a thuja. If only a few stems are affected, remove them and then water the thuja well. If half the plant is affected, you can try pruning the thuja hedge more severely.
Thuja hedges can be useful for privacy screening.
Thuja, also known as arborvitae, is one of the most popular hedge plants and has many advantages: it is an evergreen plant which is hardy enough to withstand frost, and makes an effective privacy screen all year round.
What’s more, thuja is also fast-growing, so you don’t need to wait long to enjoy a lush green, dense hedge. Our guide explains what’s important when trimming your arborvitae hedge.
Beware of poisonous hedges
Some shrubs and hedges are poisonous and thuja plants can cause allergic reactions. You should always wear gloves when touching freshly cut stem of thuja, cherry laurel and cypress. Caution should also be exercised when handling privet and boxwood. Therefore, it is important to make sure you wear the right protective clothing when shaping and maintaining your hedge as well as when shredding cuttings.
If you are planning to trim a hedge, there are a number of botanical and legal considerations to take into account. From a botanical perspective, the period between April and September is a suitable time for pruning thuja. If you only trim your arborvitae once a year, the best time to do so is in early summer towards the end of June. However, if you plan to trim it three times per year, you can plan this for the beginning of April, the end of June and the end of August. You should not trim thuja further after September, as new growth won’t have time to mature before frost sets in, and it may be damaged.
How often you should trim thuja plants depends on the age of your thuja hedge. We recommend trimming young thuja hedges twice a year, so they can form many small side shoots which will quickly make the hedge dense and opaque. A yearly pruning is often sufficient for an older arborvitae, though you should trim fast-growing varieties twice a year even if they are older.
What is the legal situation when it comes to trimming your thuja? The German Federal Nature Conservation Act (Section 39(5) no. 2 BNatSchG) prohibits the trimming of arborvitae hedges during the breeding season between 1 March and 30 September because many bird species raise their young during this time. If you only need to trim back or slightly tidy up growth without affecting the main body of the hedge, you may trim your thuja during this period.
In many places, there are also legal requirements concerning the maximum permissible height of your thuja hedge. The height your thuja is permitted to reach depends on your location. In many German municipalities, the limit is two metres. It is best to find this out directly from your city or municipality before trimming your thuja.
In order to trim your mature thuja hedge correctly, you will need the right tools and utensils to hand – find out what you should have ready before you start!
Working with high-performance power tools is fun and allows you to broaden your skills, which is great if you can rely on effective and safe protective clothing. Always wear your personal protective equipment when working with STIHL power tools. Find out more in the owners manuals for your product. Before using your power tool for the first time, fully familiarise yourself with it and ensure that it is in flawless condition before each use. On request, your STIHL dealer will be happy to prepare your power tool for its first job, and will also advise you on models and sizes of protective clothing that you can try on at your leisure. Please remember that personal protective equipment is no substitute for safe working.
To keep your thuja hedge healthy and beautifully shaped, you should trim it back regularly from the second year of growth. Even if your thuja hedge hasn't yet reached the desired height, you should reduce the length of the previous year’s uppermost stems by half to achieve dense growth. Read on to find out how to trim your thuja.
When preparing to trim your thuja, you should first select a suitable time. We do not recommend trimming it when the sun is shining brightly, as this will cause the fresh cuts to turn brown. You should also avoid trimming thuja while it is wet, in order to prevent fungal infestation and hedge diseases. A dry, cloudy day with no frost is ideal.
As thuja is poisonous, it is important to wear garden gloves, safety glasses and long clothing before getting to work.
Make a “brick line” along the top of your thuja by stretching twine horizontally between two points to act as a guide for trimming the hedge. If you are experienced at trimming hedges you can skip this step. It is also a good idea to place a tarpaulin under the hedge to catch the cuttings, so that it’s easy to later dispose of them quickly and cleanly in the garden waste bin. If you want to compost the thuja cuttings, you should shred them and mix them with materials that will decompose quickly.
Use a clean, sharp cordless hedge trimmer to prune your thuja into a trapezoidal shape – wider at the bottom and tapering upwards. This means that all branches of the hedge will get enough light and will also ensure that not as much snow ends up accumulating on your hedge in winter.
STIHL tip: Never cut beyond the green part of a stem, as the old woody branches of the thuja will not resprout. This means that it’s a good idea to prune carefully and gradually work your way up with the hedge trimmer, as the sensitive thuja will not forgive any slip-ups.
You should never leave the cuttings behind on the ground after trimming the hedge. If the thuja is healthy and free of pests, you can dispose of the hedge trimmings in the compost. Please note, however, that thuja breaks down slowly. Shred the leftovers thoroughly and mix them with other cuttings so that the compost does not become overly acidic.
After trimming the toxic thuja hedge, please be sure to thoroughly disinfect the power tools you have used. You should also clean your hedge trimmer.
The most popular thuja varieties in Germany include thuja brabant and thuja smaragd, also known as the thuja emerald. Both are frost-hardy, but while the thuja brabant is more of a light green hue, the thuja emerald – as the name suggests – is a striking dark green colour.
For the comparatively slow-growing thuja emerald, which grows around 10 to 15 centimetres per year, it is advisable to trim the stems once a year, while for the thuja brabant with annual growth of around 30 centimetres, we recommend regular trimming.
Thuja needs sunlight in order not to turn brown.
To care for your thuja, you should fertilise the hedge regularly and remove smaller shoots. It is also important to identify hedge diseases and treat them when they arise. Look for shoots that have dried out, died or been affected by disease and remove them carefully and completely.
To ensure that your thuja gets enough sunlight and to maintain good air circulation, you should plan on trimming your arborvitae hedges regularly.
When doing this, always remove the smaller of two crossing branches, directly at the V-shaped connection. You can pull in and tie up adjacent branches to fill gaps in the hedge and effectively conceal individual bare areas.
