Magnesium for Tomatoes.

For the past two weeks Saturday Swot Shop has been looking at plant nutrition. In particular, phosphate and potassium, 2 of the 3 main nutrients, nitrogen being the 3rd.
 
Today’s Swot Shop considers magnesium.

Whilst not one of the main 3, magnesium is still essential for a plant’s growth and magnesium deficiency often crops up as a concern to the tomato grower.

What are the signs of magnesium deficiency ?

• Yellowing leaves, yellowing between the veins of the leaves with the veins remaining green. The yellowing first shows up on the lower leaves and then moves up.  As the plant continues to be affected leaves will turn completely yellow, wither and the growth of the plant will be stunted.
• However, it is also worth bearing in mind that in healthy mature plants old leaves at the base of the plant will often turn yellow and then brown as part of the natural ageing process.

Is it true that tomato plants are one of the plants most affected by magnesium deficiency ?

• Yes. High concentration of potassium in the soil inhibits the intake by the plant of magnesium and of course tomato feed and fertilizer is high in potassium.

Are some soil types are more prone to magnesium deficiency ?

• Yes. Magnesium can be washed out of the soil and so lightweight, sandy soils, acidic soils are more prone to this than clay soils, alkaline soils which are better at retention.

So what should I do to treat magnesium deficiency ?

• To put magnesium back into the ground, add Epsom Salts or dolomitic limestone to the soil in autumn and spring in anticipation of the next planting.  For more localised treatment some gardeners sprinkle a teaspoon of Epsom Salts into the planting hole before putting the plant in or sprinkle some around the base of the plant once planted.
• If your tomato plants are suffering now a quick way of getting magnesium to them is to dilute Epsom Salts in water and spray, once a fortnight, with a fine spray. This is called a foliar spray. Liquid seaweed can also be used as a foliar spray. (Refer to individual product details for recommended dilution ratios.)

Epsom Salts; I thought they were for the bath ?

• They are. In fact used as a bath soak it’s good for aching muscles. Ideal for tired gardeners. But you can also get it for gardening purposes from gardening suppliers.

And what does a plant need Magnesium for ?

• It’s needed by plants to make the green pigment, chlorophyll.

Chlorophyll, hmmm sounds vaguely familiar. I seem to remember it had something to do with photosynthesis.  Can you remind me what ?

• Hmmm. I feel a caffeine deficiency coming on. Let’s save that for next week.

Photo by Rob Gale

Tagged as: epsom salts magnesium, magnesium deficiency tomatoes, magnesium for plants, seaweed plant food