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Tomatoes Magnesium Deficiency – Yellow Leaves, Epsom Salts

This is a problem where the plant looks like it has a virus with yellowing leaves but it is caused by lack of magnesium. If in doubt as to the cause, treat as if it is magnesium deficiency. It can do no harm to try!

Chlorosis Magnesium Deficiency Tomato

Chlorosis Caused by Magnesium Deficiency in Tomato Leaves – University of Maine

Magnesium is an essential element for plants as it is required in the chlorophyll molecule. Chlorophyll is the chemical that enables the solar power plant to work – producing starches and sugars etc from other chemicals taken up by the roots.

Chlorophyll is what gives the leaves their green colour and yellowing of leaves is always a sign that things are going badly wrong.

It can happen to any plant and the cause need not be magnesium deficiency. Iron deficiency also causes yellowing leaves with deep green veins and nitrogen deficiency can cause yellowing leaves.

When it happens to tomatoes, especially greenhouse or container tomatoes you can be 99.9% sure of the cause. The use of high-potash tomato fertiliser has had the unwanted effect of locking up the soil or compost and the plant is failing to get the required nutrient balance.

The better and more expensive tomato fertilisers usually include trace elements and magnesium to prevent this problem from occurring

Curing Magnesium Deficiency in Tomatoes

Happily curing the problem is remarkably easy and just requires you to foliar feed the tomato plant with common or garden Epsom salts.

Epsom Salts Foliar Feed – Recipe

Dissolve ½ oz in a pint of water or 20g per litre of water. It’s easiest to dissolve the salts in warm or hot water but allow to cool to ambient temperature before using.

How to Foliar Feed Epsom Salts

Foliar feeds are best applied in the morning before the day gets too hot and the plant closes the pores in the leaves to conserve moisture.

Spray from top to bottom paying particular attention to the underside of the leaves where the pores that absorb the feed are concentrated.

Spray well so the leaves are wet and dripping every day for a week and the problem should be solved.

Preventing Magnesium Deficiency

Do not over apply high-potash tomato fertilisers. It’s always a temptation to use a little extra thinking this will result in more and better crops. Unfortunately the opposite can result.

It’s true that tomatoes require frequent feeding to give of their best but it’s often worth replacing one in three feeds with a standard balanced liquid fertiliser or high nitrogen fertiliser such as Miracle Gro to avoid overdosing on potash.

Swap to a good quality tomato fertiliser that has magnesium added as a trace element.

For greenhouse borders or growing outdoors where there is a magnesium deficiency, increase the pH by using Dolomite lime that has magnesium rather than the usual ground limestone.

The addition of Keiserite which is the mineral that Epsom salts are made from will cure shortages

Further Information: Tomato Growing Guides