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]Hey there,

I have a variety of tomato plants (as well as loads of other edibles) in containers and in the ground (red clay soil). I am living in tropical Indonesia by the way. Only on one of my tomato plants in the ground I noticed that on two of the lower sets of leaves the edge of the leaf is turning yellow. What nutrient deficiency is it? Magnesium? Potassium? Or something else?

Thanks.

Yes, magnesium deficiency can result in chlorosis like that, with leaves yellowing, but veins staying green. Iron deficiency can also, but in iron deficiency the chlorosis is usually at the base of the leaves near the stem, not at the outer edges like yours.

You can buy special magnesium nitrate fertilizer, but any good complete organic fertilizer should do. Magnesium deficiency occurs most often in strongly acidic, light, sandy soils, where magnesium can be easily leached away. Excess potassium, generally due to fertilizers, further aggravates the stress from the magnesium deficiency.

Hey rainbowgardener,

Thanks for the reply. I thought perhaps it was magnesium. Interesting info about excess potassium exacerbating the issue. Only recently I added some high liquid potassium and phosphoros feed as the plant is flowering. I recently bought some organic granular well balanced fertilizer which I will grind up and add just below the surface of the soil.