Magnesium Deficient Plants

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Sick citrus leaf

Magnesium Deficient Plants

Don looked at a citrus tree with a magnesium deficiency. Magnesium is moved in plants from old leaves to new growth and to developing fruit. When a magnesium deficiency is present, the young citrus leaves appear green and normal, but older leaves turn yellow and often have an inverted ‘V’ of green at the leaf base. In advanced cases, leaves fall prematurely and cropping declines. Magnesium deficiency is more likely to occur in acid soils, but it also occurs in alkaline soils.

After clearing away weeds, agapanthus roots and old weed mat around the base of the tree, Don applied Epsom salts (magnesium sulfate) dissolved in water at the rate of 2 teaspoons of Epsom salts per litre of water. For a quicker result, an Epsom salts solution can be applied as a foliar spray.

Fertilise your citrus

Citrus trees can live in pots for many years, if you look after them. The one in our segment was close to death! Don repotted it in fresh potting mix, watered it and gave it a feed of complete citrus food. Citrus trees are known as ‘gross feeders’. Unless they are fertilised regularly they can develop trace element deficiencies, such as the one described above.

To fertilise a full grown citrus tree spread about 1.5-2 cups of fertiliser, such as Yates Gro-Plus Citrus Food, under the tree to the drip line where the feeder roots are to be found. The drip line is the line of the outer edge of the branches where the drips from foliage would fall. Water well after applying fertiliser. Fertilise in spring, and repeat the process in late summer. It is good to alternate fertilisers – say citrus food in August/September and Dynamic Lifter in February.

Citrus in tubs need small amounts of food frequently. Either fertilise every four to six weeks from spring to late summer with a small amount of either Dynamic Lifter or complete citrus food or use a slow release fertiliser such as Osmocote Plus.

Gardenia with yellow leaves

Don explained that most gardenias with yellow leaves are suffering from nitrogen deficiency, and they respond to a feed of duck or chicken manure. The plant he looked at in the segment was also showing signs of magnesium deficiency, so it was treated with Epson salts, as above. (Tip: always water plants well before and after fertilising.)

Further information

Yates Gro-Plus Citrus Food costs approx. $8 for 5kg, and Dynamic Lifter fertiliser costs about $12 for 15kg. They are available at nurseries and garden centres. Epsom salts is readily available from supermarkets.