As soon as the needles of the thuja change color, this is an indication to the gardener that something is wrong with the tree of life. Care errors are often responsible for the shoots turning brown, yellow or even black. What diseases turn the needles of thuja black?
Why do thuja needles turn black?
Black needles on the thuja are usually not a sign of disease, but rather indicate a manganese deficiency caused by unfavorable site conditions such as compacted soil, waterlogging or too acidic substrate. A fungal infection can also cause dark needles.
What diseases cause thuja shoots to turn black?
Black shoots of thuja are not diseases. They are almost always a sign that the tree of life is lacking something, namely manganese.
Occasionally a fungal infection can also cause very dark needles.
Black needles due to manganese deficiency
Manganese is usually found in sufficient quantities in the substrate. However, if the site conditions are unfavorable, the tree of life cannot absorb sufficient manganese through the roots, for example:
- compacted soils
- Waterlogging
- to acidic substrate
An unfavorable location for the hedge is where the soil is too moist or even forms waterlogging. On very acidic soils, the tree of life needs more manganese than on pH-neutral soil.
Have the substrate examined in the laboratory. If the pH is below 6, the soil is too acidic. The pH value should then definitely be increased.
Treating manganese deficiency in thuja hedges
After black needles appear on the tree of life, first loosen the soil and ensure better drainage as much as possible.
Treat excessively acidic soils with lime. This increases the pH value so that the hedge needs less manganese.
You can simply cut off the black shoots and dispose of them in the compost.
Fungal infestation turns needles dark
If the needles of the Thuja become dark brown or almost black, there may also be a fungal infection. It occurs more often when the plants are very dense or the weather is generally very humid.
Cut off infected shoots generously and dispose of them in household waste, not in the compost!
If the infestation is severe, use a broad-spectrum spray against fungal diseases. The temperatures should not be below 6 degrees.
Tip
Before planting a thuja hedge, you should work the soil well. Remove all thickenings and, if the soil is very solid, create drainage. Heavy soils are loosened by adding compost or sand.
