Advice 1: Why leaves turn yellow

With the arrival of autumn sky cloud heavy rain clouds, sunlight becomes less, the foliage of trees and grass turn yellow and eventually fall off. Why in this gloomy time of year the leaves become yellow it?
Why leaves turn yellow
Instruction
1
Yellow color appears in the foliage of nowhere at the wave of a magic wand with the onset of autumn, it is always present in it. The yellowness give the leaf colour substances called carotenoids. Their impact on leaf color is shown only when it begins to weaken the "green" chlorophyll, the substance which is produced in large quantity only by the action of abundant sunlight.
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When the summer passes, the sun is getting smaller, and the chlorophyll is gradually destroyed and ceases to absorb sunlight. The role of the main "colors" of the leaves is transferred to the carotenoids, pigments, orange and yellow colors.
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Not only the lack of sunlight can cause yellowing of the foliage. This can occur during a drought when the leaves are not able to get the necessary amount of water. Plant shedding of leaves to conserve moisture. Drought affects wild plants, in the first case due to the lack of rain and the second because of the dry air, inadequate watering, tightness pot, etc.
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Yellow color can cause the lack of mineral salts so necessary for the synthesis of chlorophyll. It is nitrogen, iron, magnesium.
Another reason for the yellowing of the leaves – the parasites. The leaves or roots of plants are attacked by viruses, bacteria, mites, etc. in addition, a houseplant may receive mechanical damage during transplantation or from accidental or deliberate actions of the little inhabitants of the house, children or Pets.
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Why do leaves turn yellow before fall, and not fall off the green? The answer is simple: a tree or plant takes all the remaining valuable substances in the roots or branches, and "pumps" in senescent leaves food selection. Thus, we can conclude that carotenoids are not for the sustenance of plants are important substances.
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Leaves of different plants turn yellow in different ways. For example, birch leaves and limes begin to change color in August, in early September, the yellow maple, then aspen. Each plant has its own biological clock, which occurs with seasonal changes.

Advice 2 : Why yellow lower leaves of tomatoes

Yellow, which begins to appear on the leaves of tomato, always has a cause, and often not even one. Its occurrence may contribute to at least six negative factors. They need time to find and fix.
Lack of vitamins, illness or improper care - all these can cause yellowing leaves tomato
Instruction
1
The first reason may be the incorrect operation of the root system. This happens most often with seedlings in pots or when planting overgrown seedlings in the ground. Tomatoes like a lot of space and quickly build up the roots. If the volume of soil in the pot is insufficient, the seedling grows, the roots densely entwine earthen and when planted in the soil begin to actively grow the young roots. Old leaves turn yellow, because all the power goes to the formation of roots. Seeds should be planted in the container medium in size and planted in the ground, when the ground ball is not yet fully braided roots.
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Hypothermia is the second cause of yellowing leaves. It can be as hypothermia green parts of the plant and soil. He disrupted the root food. All the leaves on the stem acquires a yellow tint with blue. This can impact negatively on plants at any phase of development. Therefore, fluctuations in temperature when growing tomatoes it is better to avoid.
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Root damage that can occur when transplanting seedlings or when loosening can also cause staining of the lower leaves of tomatoes to yellow. In order that the yellowing is gone, the plant needs time to grow new roots and leaves. Then the green coloring of leaves usually is restored.
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Yellowing of foliage of tomatoes can react to the lack of moisture. Tomatoes – drought-resistant plants. The bushes but the adults have a taproot length of one meter. And moisture the plant gets from the soil with the aid of this root. Therefore, if irrigation of tomatoes is carried out superficially, and the moisture does not reach the deep layers of the soil, plant the liquid does not. Tomatoes should be watered rare, but abundant.
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The lack of trace elements needed by the plant also affects the leaves. If a plant lacks nitrogen, the leaves appear yellow spots. If it lacks calcium, yellowing of apical leaves. Lack of copper leads to pallor and yellowing of the lower tier of leaves. If the soil lacks sulfur, the leaves just turn yellow and thicken and harden. The lack of manganese and iron leads to yellowing and drying of leaves on the whole plant. Also the leaves turn yellow from the edges with a shortage of magnesium. And the shortage of phosphorus in yellowish hue is painted just the tip of the leaf, whereas its abundance – its entire surface completely.
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Fusarium is the most serious reason that can yellow the leaves of tomato. This is a fungal disease that is easy to detect, because in addition to yellowing, the leaves and lose their turgor, become flaccid, as if they have not been watered. Against Fusarium it is better to undertake preventive measures. But if the disease has begun, it is necessary with an interval of 10-12 days to spray the bushes antifungal biologics like "fitosporin" and "Fitotsid".
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