Anna EvangeliDo gardenias need Epsom salts?

If you type ‘gardenias’ and ‘Epsom salts’ into Google, you’ll find a range of gardeners keen to share their love affair with this cheap and available plant tonic.

Gardenia foliage end of winter

Gardenia foliage end of winter

Dissolving some of the white crystals in a watering can, then dowsing the root zone with it is supposed to bring yellow-leaved gardenias back to life, especially in springtime.

The thinking behind this practice is that the yellow leaves are a sign of magnesium deficiency. Adding Epsom salts, or magnesium sulfate, is supposed to replenish the missing magnesium, perking up the gardenia in the process.

Epsom Salts photo Kazuhiro KeinoSome gardeners recommend a one-off dosing, others a feed at regular intervals.

The Epsom Salt Council – a body that promotes Epsom salts for a manner of health, beauty and gardening reasons – recommends application every 2-4 weeks for acid-loving shrubs.

But not everyone agrees.

Don Burke, an Australian TV gardener, says the yellow leaves aren’t a sign of magnesium deficiency at all but a sign that the plant has suffered in winter.

“The problem is caused by cold damage, rather than a mineral deficiency,”

he writes in The Complete Burke’s Backyard: The Ultimate Book of Fact Sheets.

“So forget the Epsom salts. Instead, give your gardenias a good feed in spring, using some aged chicken or duck manure.”

Associate Professor Linda Chalker-Scott, a US urban horticulturist at Washington State University, also doubts the power of Epsom salts.

Gardenia Photo NatalieMaynor via Flickr

Gardenia Photo NatalieMaynor via Flickr

When she reviewed the scientific evidence for applying it to garden plants, she didn’t find anything robust enough to recommend it.

Any evidence she did find was from studies on commercially grown plants, none of them gardenias, that were suffering from known magnesium deficiency. Nothing on use in the home garden, nor on plants whose magnesium status was unknown.

She also says that claims it makes plants grow bushier don’t stand up.

Could it do harm? Isn’t it worth giving it a try anyway? Surely, thousands of gardeners can’t be wrong.

She says that as Epsom salts is so easily soluble in water, it’s easy to overdo a dosing and cause run-off. She concludes:

“It is irresponsible to advise gardeners and other plant enthusiasts to apply Epsom salts, or any chemical, without regard to soil conditions, plant needs, and environmental health.”

Gardenia foliage - magnesium deficient?Even if the plant is magnesium deficient, adding Epsom salts won’t always fix things, she says. This might be the case with soils heavily leached by rainfall or suffering from too much potassium.

What might help, she says, is boosting soil nitrogen, which better allows some plants to take up magnesium from the soil.

So, along with Don Burke, that’s two recommendations to give your plants a nitrogen boost with a good feed and ditch the Epsom salts.

[Republished, with permission, from The Geeky Gardener]

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Anna Evangeli

About Anna Evangeli

The Geeky Gardener is Anna Evangeli, a former news editor at ABC Science, the Australian national broadcaster’s science website, and science correspondent for Gardening Australia magazine. The Geeky Gardener looks after a lush, inner-city garden in Sydney, Australia. When she’s not geeking or gardening, she teaches journalism at the University of Notre Dame, Sydney.

4 thoughts on “Do gardenias need Epsom salts?

  1. Peter Whitehead on said:

    Hi Anna
    I was always told that the yellowing leaves on Gardenias at this time of the year was due to 2 things: lack of consistant watering (people forget in winter) and that they need a jolly good feed. In my 23 years of owning a garden centre, I always tried to steer the client away from the ES Cure!
    Peter Whitehead – Ross Tour Leader

  2. Laurel on said:

    Thx for this info – so what about the other recommendation we often hear for yellowed acid lovers – iron via iron chelates? And while I am asking about acid lovers…..have heard/read I should add lime to my compost heap to sweeten it. How long should I then leave it before using it on the things which hate lime – azaleas, gardenias etc?

    • Laurel
      Chelated iron is soluble form of iron watered over plant to green up plants that are yellowing due to alkaline soils. These plants are referred to as chlorotic. When the leaves are yellow the plants can’t photosynthesise. Iron in the soil is unavailable due to the high pH but the plants can take it in if the soluble form is used. Plants usually regreen after an application of chelated iron but as the pH hasn’t changed, they’ll yellow again.
      With the compost – it is usually unnecessary to add lime to compost heaps and yes it would cause the compost to become alkaline. ‘Sweeten’ is a term that’s used to mean make it more alkaline. Aerate the compost and make sure you have a balanced amount of wet and dry material going in to the heap and it should be okay. The warmer conditions ahead will also boost composting. If you are concerned about the pH of compost, give it a pH test before you go to use it.
      Best wishes
      Jennifer

      • Laurel on said:

        Thank you .

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