The key component of any plant is chlorophyll. Thanks to it, a vital connection is established between the sun and the biosphere: the chlorophyll contained in plant cells synthesizes organic substances from water and carbon dioxide under the influence of sunlight. Yellowing of the plants indicates a violation of the formation of chlorophyll in them - a disease called chlorosis. So the answer to the question of why tomato seedlings turn yellow is pretty simple. But this alone is not enough - you have to get to the reasons. And there are several of them.
The most common of these is malnutrition of the root system. This happens because of its damage, physical or temperature (hypothermia). But if the temperature regime is violated, chlorosis affects the whole plant. And if, say, the planting of
tomato seedlings on a bed led to mechanical damage to the root system, only the lower leaves turn yellow. In this case, you should wait for the seedlings to root and the appearance of new adventitious roots - the tomato will cope with chlorosis on its own.
To determine the cause of chlorosis, it is enough to carefully look at the leaves of a young plant. And if
tomato seedlings turn yellow from older (lower) leaves, it is worth suspecting also the lack of one of the chemical elements important for the tomato.
Most often, chlorosis of tomato seedlings indicates a nitrogen deficiency. About it speak and leafy veins of bluish-red color, and small leaves on the whole plant as a whole. The lower leaves die after yellowing. If seedlings are grown for sale, you don’t even have to try to bring them to the market: obvious signs of chlorosis will scare away buyers from it, and no explanation of why tomato seedlings turn yellow will not help.
Yellowing can also cause potassium deficiency, but here the process often goes too far due to the accumulation of ammonia nitrogen, accompanied by dehydration of the leaves and their twisting, until signs of tissue necrosis appear.
The next reason why tomato seedlings turn yellow is zinc deficiency. He also gives himself out as small numerous yellow dots on young leaves. They are also abnormally small, can be entirely yellow, sometimes twisting up.
Tissue necrosis, in contrast to
potassium deficiency, manifests itself immediately over the entire surface of the leaf, but passes much faster.
If chlorosis of young leaves of seedlings starts from their base, and the color from yellow-green through lemon-yellow becomes yellow-white, then the plant responds to iron deficiency. It is reflected only on young leaves, not moving to older ones. This type of deficiency can happen at an early stage of seedling cultivation if its round-the-clock highlighting is not supported by top dressing with iron content. One has only to resume them, as the plant comes to normal in just a few hours.
But micronutrient and nutrient deficiencies are relatively easy to fix. It is quite another matter when the answer to the question of why tomato seedlings turn yellow is as follows: this is fusarium infection. This dangerous fungal disease can affect tomatoes at any age. It is also difficult to deal with it because the disease can be revealed too late. The most effective remedy for
Fusarium wilting is prevention. But if the seedlings are already affected, it is necessary to immediately isolate healthy plants from the sick; the first to be treated with the drug, the second to be destroyed immediately (burned).