Magnesium is an essential nutrient that is used by all green plants to make chlorophyll, which is vital for photosynthesis.
The first sign of deficiency generally appears on the lower half of the plant/s, and is recognized when a yellow discoloration appears between the leaf veins.
There could also be signs of premature autumnal leaf tints and dying leaves.
If left untreated this problem will move higher up the plant/s.
Magnesium deficiency is common on acid, sandy soils, with low organic matter levels, or where heavy applications of potassium rich fertilisers have been made.
To be sure that it is lack of magnesium in the soil rather than failure to of plants to take up magnesium a soil test is advisable.
Sometimes if the pH is not quite right this will prevent plants taking up magnesium.
Low soil pH decreases the magnesium availability, and high soil pH increases availability.
Low soil temperatures can also affect a plants uptake.
In spring top-dress the bed/s with of Epsom salts (magnesium sulphate) applied at a rate of 30g (1oz) per sq m.
Apply the top dressing to a moist bed and wash off any that comes in contact with the plants.
If symptoms appear during the growing season, apply a foliar spray* containing Epsom salts at 20g (½oz) per litre of water.
*Adding a few drops of washing-up liquid to this mix will help the solution stick to leaves.
Don’t spray in bright sunlight, to do can result in scorched leaves.
Repeat the treatment three times at fortnightly intervals.