Whether as a pictorially formable solitary plant or an opaque hedge, the thuja is one of the most widespread ornamental trees in private front gardens and gardens. Despite intensive growth and comparatively simple care, plants keep turning from the usual rich green to brown. We explain the causes and measures to get a fresh, healthy green out of the unwelcome brown.
Table of Contents
From cause to remedy
Understandably, hobby gardeners and garden owners are primarily interested in how they can make their tree of life shine green again as quickly as possible. Due to the different causes that can lead to the unloved brown discolouration, however, the countermeasures are also very different. A remedy without knowledge of the cause is therefore hardly possible effectively and would at best be a lucky hit.
Brown equals dry?
Browning of plants or parts of plants is usually accompanied by the affected shoots or leaves drying up. Because tanning usually results from the lack of plant sap and the closely related breakdown of chlorophyll. Dry does not always mean complete drying out and dying. In this case, a remedy would hardly be possible, since completely dried-up pathways in the thuja are usually so badly damaged that revitalization is hardly possible. Instead, the browning usually occurs when the water content drops, so that with an early reaction a revival and a return to the green color is quite possible.
winter tan
Our first case is a special case, since there is no impairment, disease or damage here, but the brown color simply follows an adaptation of the plants to winter cold periods:
- Winter tan Originally, wild Thuja adapted to the extreme frosts of its North American homeland
- Browning beginning in late autumn and disappearing in spring with the onset of the growth phase
- occurring in wild species and old cultivated forms
- modern cultivated forms no longer have a winter tan
- BUT: Winter tan indicates that the tree of life is more frost hardy
dryness
A lack of precipitation, as well as insufficient watering or simply the inability of the plants to absorb the available water, leads to a low water content in the tree of life with progressive browning of the leaves.
Requirements:
- dry summers
- cold winters
- Frozen soil (then the roots cannot absorb water)
- Strong, dry winds
Measures:
- Ground covers made of bark mulch etc. to counteract dehydration
- Regular watering, in winter on frost-free days
- Preventing the onset of frost by watering intensively to fill water reservoirs in the soil and plants
salt
Whether road salt or the well-intentioned use of blue grain, the Thuja reacts sensitively to any form of salt if it affects it too intensively. The result is brown discoloration of the shoot tips, later of the whole shoots. A remedy for the plant is possible, although the affected shoots are usually lost.
Remedy:
- Cut off and discard dried thuja shoots
- Rinse the plant and rinse off salts from spray water etc
- Water the soil well to wash out salts into deeper soil layers
- Reduce mineral nutrients initially to normalize water balance
Acid soils
If the soil around the thuja has an acidic pH value, it usually accumulates a large amount of free manganese. The plant reacts to this with brown-black discoloration of the needles in connection with increasing dehydration.
Remedy:
- Work soil-acidic lime into the soil
- After two to three months, add compost and rake in to even out the soil’s nutrient supply
Diseases
Various diseases can also cause thuja shoots and leaves to dry up and turn brown. In most cases, these are fungal diseases, such as:
- Pestalotia-Triebsterben
- Needle or dandruff tan
- Kabatina-Triebsterben
What they all have in common is the fungus as the pathogen, as well as the spread from the young, particularly susceptible shoot tips. The main way to remedy this is to take quick and targeted countermeasures:
- Cut back affected shoots
- Spray on fungicides
- Prevention by balancing the nutrient balance to reduce susceptibility (especially magnesium and calcium)
