Yellowing, and sometimes even browning, of needles is undoubtedly one of the issues that most often keeps conifer enthusiasts awake at night. But why is it that, despite the fact that many of them tolerate poor soils, they eventually start to show signs of nutrient deficiency?
It seems that the cause of this phenomenon lies primarily in the specific requirements of not so much wild conifer species, but rather the cultivated varieties derived from them.
These are most often planted in flower beds. The needs of ornamental varieties are usually greater than those of their wild ancestors, and the simplest way to meet them is to plant them in holes amended with a ready-made substrate for conifers. It contains not only peat and wood fibres, which together create a proper soil structure, but also all the nutrients required by conifers. One of them is magnesium, which is used in the formation of chlorophyll molecules.
There are also other, much more serious causes of browning in conifers. One of them is phytophthora, a root disease that damages the underground parts of the plant so severely that, in extreme situations—such as during drought or frost—the roots cannot keep up with water uptake. As a result, the upper parts respond by turning brown.
If conifers are growing near a busy road, the cause of damage may be salt used for winter road maintenance. Harsh winter winds can also cause damage.
There is yet another reason for needle discoloration, but this one is linked to the natural winter behaviour of plants. Many pines simply turn yellow during the cold, short days. It is their unique way of welcoming the arrival of winter!
