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How to Deal With Magnesium Deficiency in Plants


You may find that no matter what you do, your plants fail to thrive.  You may have prepared the soil, watered and mulched but growth is slow, leaves are yellow or reddish, and there is poor flowering.  This could be a sign of nutrient deficiency, whether it is a nitrogen, magnesium or potassium deficiency.

The plants most at danger of nutrient deficiency are those in containers, where the soil can become imbalanced, either too acidic or too alkali.  You are more likely to experience this in spring and summer.  Magnesium deficiency is one such nutrient that you will need to manage, here we offer some hints and tips to support you in building a healthy garden.

What are the symptoms of magnesium deficiency?

How to deal with magnesium deficiency in plants starts with identifying the problem.  Plenty of other nutrients could be deficient, such as phosphorous, nitrogen, potassium, manganese and more.

You will notice a yellowing between the leaf veins with magnesium deficiency.  This is called interveinal chlorosis, and it will impact the older leaves first.  Sometimes, there may be red, brown tints to the leaf and there may be an early leaf fall in late summer.   Without magnesium, the chlorophyll in the leaves begins to degrade.  It will also cause poor flowering or short lifespan of flowers.

Some plants are more prone to magnesium deficiency than others.  You will find that tomatoes, apples, grape vines, roses, raspberries and rhododendrons are all demanding of magnesium.

What are the causes of magnesium deficiency?

Magnesium is essential for the healthy leaf to harness the energy from the sun, for the purpose of photosynthesis.  Light, sandy soils are more prone to a lack of magnesium.  However, if you use high-potassium fertilisers, particularly if you are using tomato feed, then you can create a deficiency in this nutrient.  The plant will choose to take up the potassium over the magnesium when a balance of both is essential to healthy growth.  It is also possible that heavy rainfall can leave magnesium out of the soil, particularly highly acidic soil.

Be aware that overuse of one nutrient can cause a deficiency in another.  No damage can be done by pouring lots and lots of magnesium into your soil, as it is Ph neutral and can do little harm.  However, it may prevent the uptake of potassium and calcium.  Therefore, the likely cause of most nutrient deficiency is an imbalance in the soil.

How can you remedy magnesium deficiency?

Your first solution will be Epsom salts.  Epsom salts are an essential feed for high foliage plants in the summer.  To apply, you should dilute the salts, with 20 grams of salts per litre of water.  Try using your Epsom salts mix fortnightly, maybe two or three times over the summer months.  Remember that spraying in dull weather is always best, as you will want to avoid scorching to the leaves.

You may need to take a long-term approach to the rebalancing of nutrients in your soil.  You may want to apply calcium-magnesium carbonate, which is also known as Dolomite limestone, in autumn and the winter, and you will rectify the problem for the next year.  This limestone mix will make the soil more alkaline.  Therefore, your pursuit of the correct soil balance means that you cannot use this mix where you hope to grow acid-loving plants such as ericaceous or rhododendrons.

In short

It is tricky balancing the nutrients in the soil, especially when your only clue is the leaf growth and the health of the flowers.  It is harder still when the solution to one symptom may be the cause of your next.  However, magnesium is essential to photosynthesis, therefore plant health.

Check for yellowing on the leaf and early leaf fall.  You can make a quick decision to add Epsom salts or choose to take long-term action with Dolomite limestone.  Whatever you choose, be sure to remember the importance of potassium and calcium, which can be blocked by too much magnesium.   It is easier than it sounds to maintain the health of the soil – it is just about observation and moderated action.

Anna Sharples

Anna is the marketing and office manager for Garden Benches - a premium supplier of high-quality wooden benches and other outdoor furniture.

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