One of the most essential minerals required for healthy plant growth and development is magnesium. It is the building block of chlorophyll that makes the leaves appear green in color. In the structure of a chlorophyll molecule (C55H72O5N4Mg), magnesium is the central atom.
Chlorophyll is very important for the process of photosynthesis that is, the process of making food and energy within the plants. Thus, magnesium deficiency in plants can lead to many kinds of problems.
Magnesium deficiency can be due to a very wet, acidic or cold root environment. It can also occur due to a high quantity of potassium and calcium in the soil as compared to the level of magnesium. The root system becomes limited and the plant being heavy, demands more magnesium than the supply available.
A deficiency in magnesium can lead to many visible symptoms. These symptoms are usually observed in lower and older leaves. The deficiency leads to chlorosis and necrosis of the leaves. The lower and older leaves develop interveinal chlorosis. The initial symptom is generally a pale green color that is very pronounced in the lower leaves.
The leaf margins may curve upward and may turn red-brown to purple in some plants. During the pre-harvest season, deficiency may lead to leaf drop, weak stalks, and long-branched roots. The older needles in conifers may become yellow.
The new needles in the lower region may turn yellow in some conifers. Other symptoms include orange-yellow chlorosis in older leaves: the green color on the leaves have the appearance of 'strings of beads' that look like yellow and green stripes running parallel to one another.
Magnesium deficiency in plants leads to reduction in yield and stunted growth. It also leads to increase in susceptibility to disease and finally, death of the plant. It is very common in tomato and potato plants, and in fruit trees like apples, currants, and gooseberries.
This is due to the high potassium levels that are required for higher yields of these plants. This excess potassium causes the locking up of magnesium, making it unavailable to the plants.
How to Treat It
Treating magnesium deficiency is very easy. Plants can absorb magnesium through a process called foliar feeding, which is nothing but applying the magnesium solution on the leaves. Take 20g Epsom salt in a liter of water and spray it over the plants. Any excess solution can be fed to the root system of the plant.
You can use dolomite lime that contains 8% magnesium. You can even try using mineral kieserite to feed the plant magnesium sulfate through soil. However, make sure you do not overfeed either kieserite or dolomite lime to the plant or it will lead to potassium deficiency. Organic options include use of compost cow or turkey manure.