Is it a good idea to put Epsom salts on to tomato plants?

Tomato    FL

My friend swears by Epsom salts for her tomato plants. She says that it supplements the magnesium and prevents blossom-end rot. I thought blossom end rot was caused by a lack of calcium? Can the tomato plant really take anything up from the Epsom? If so then is there a particular concentration to use and when should I add it?

Posted by: Denice Williams (4 points) Denice Williams
Posted: April 14, 2013

dave commented,
i have been growing for over 20 years and with out magnesium your plants will suffer calcium def and iron, magnesium is a catalyst and allows the plant to break down calcium and iron so it can uptake them. it also has trace amounts of sulfer which your plants need. just because it says salt ion the label doesn't mean its harmful to your plants. if you start having any problem with your plants, the first thing you should do is flush them with PH'd water. that will relieve the lockout caused by to high or to low PH in your soil, and allow the plant to start taking up nutrients again. then if you want you can add some of what ever it is you need to correct the problem!. get yourself some dolomite lime to correct a too low or acidic soil, it also contains magnesium and calcium at about 50% calcium to 40% magnesium and 10% trace elements. and is a hell of a lot cheaper than cal mag plus. just remember that if you use epsom salt to not use more than a teaspoon per gallon of water, i use a half teaspoon per gallon on my tomato plants with every watering and they love it.
almost 8 years ago.


Hold the salts! Experts say Epsom salts don't help ordinary garden crops, and may do harm. Here are links to two good explanatory pieces on the topic: First, a newspaper article http://bit.ly/15doeLL; next a lengthier fact sheet by garden myth-buster Linda Chalker-Scott of the University of Washoington: http://bit.ly/15dmyla

Regarding blossom end rot in particular: Here's some advice from a University of New Hampshire fact sheet http://bit.ly/15dnBln:

"A common, but seldom serious disorder, blossom-end rot is caused by a lack of calcium in the developing fruits. This can occur even when there is an ample supply of calcium in the soil. Usually, the first formed fruits are the most seriously affected. The disorder starts at the blossom end of the green fruit and first appears as a dark green, water-soaked spot. It may enlarge to cover half the fruit.

"Environmental or cultural factors are usually responsible for the onset of this condition. Extreme fluctuations in soil moisture and extended periods of extremely wet weather coupled with high humidity can encourage blossom-end rot.

"Rapid vine growth early in the season, often promoted by high rates of nitrogen, can divert calcium from
the developing fruits and bring on this condition.

"Poor root growth can also reduce water and calcium uptake, encouraging blossom-end rot. Poor root
growth can be due to cultivating too deeply around the plant or by planting seedlings too early in the
season in cold soils."

Posted by: Peg Boyles (4 points) Peg Boyles
Posted: April 14, 2013

For the benefit of anyone reading this section who is not familiar with the topic, Epsom salt is an inorganic compound primarily used as a bath salt which is reputed to give relief to tired, aching muscles. It is named after the town of Epsom in England, where the substance was discovered naturally occurring in mineral springs. Gardeners have been using the substance for many years to supplement plants with magnesium, an important plant macronutrient required for growth.

First off, in response to the quote from Jeff Gillman, in the otherwise informative article in the NJ Star Ledger (http://www.nj.com/homegarden/garden/i...), in which he claims

Epsom "salt" is a misnomer, since the principal ingredients are magnesium and sulfur

Well, sorry, Dr. Gillman, Epsom salt IS, by chemical definition, a salt. It may not be something you want to season your food with, but it is a salt nonetheless. It is formed commercially either by the reaction of the mineral kieserite with water, or, less commonly, by the reaction of magnesium oxide with sulphuric acid (see Figure 1).

Both kieserite and the form of magnesium sulphate in Epsom salt (epsomite) are termed hydrated as they are associated with water molecules. Epsomite is more properly known as magnesium sulphate heptahydrate (from the Greek hepta meaning seven), denoted by the chemical formula MgSO47H2O; see Figure 1).

Magnesium sulphate can be used to treat magnesium deficiency in plants. It is often used in intensive cropping systems to meet the Mg and S requirements of the plants in magnesium depleted soils. This has led to many gardeners attempting to mimic the practice by using Epsom salts which are readily bought at most stores or pharmacies. However, salts can be easily misapplied and the underlying issues with plants in the garden should usually be treated using other means.

One of the most common causes of magnesium deficiency is the loss of nutrients through “leaching” in sandy or light soils. Leaching is the process by which nutrients are removed from soil in draining rain or irrigation water. Water drains more easily from light soil, making it more prone to leaching. This very fact is one of the reasons why the addition of Epsom salts is ill-advised. The salts dissolve in the water and are also leached away from the plant. This may not seem like a big deal but the dissolution of magnesium sulphate leads to draining water that is now contaminated with magnesium and sulphate ions. Not good.

Another cause of magnesium deficiency in some plants is an excessive amount of potassium in the soil. This interferes with absorption of magnesium through the plant roots, even if is is in plentiful supply. The answer here is clearly not to supplement magnesium. It is to dilute the potassium to less harmful levels for the plants. The recommended method is to supplement soil nitrogen.

In heavy clay a more long term solution would be to loosen and amend the soil to make it more permeable to ensure nutrients are easily available to the plant.

Posted by: Lindsay McMenemy (4 points) Lindsay McMenemy
Posted: April 15, 2013

Tanya in the Garden commented,
I can confirm that the best use of epsom salts for gardeners is to soak sore muscles. I took an epsom salts bath once after spending a day loading a u-haul truck by myself, and I was not sore the next day. After a bike accident, I soaked my bruised foot in epsom salts each day to help it heal faster.
over 11 years ago.

With respect to the question of whether supplement magnesium prevents blossom-end rot: No, it will not prevent blossom-end rot. In fact, if anything, it may encourage blossom-end rot.

Blossom-end rot is a disorder caused by a calcium deficiency (not a magnesium deficiency). There's a great thread here on PlantVillage about blossom-end rot and how to prevent it: https://www.plantvillage.com/posts/46...

Excess ammoniacal nitrogen, potassium, or magnesium will compete with calcium uptake. So unless you have a demonstrated magnesium deficiency in your soil (which is very unlikely) then adding Epsom Salt will make matters worse from the perspective of blossom-end rot prevention.

Posted by: deactivated (25 points) deactivated
Posted: April 16, 2013

From what I have learned from experienced gardeners and farmers is that most of the soil in the US is high in magnesium, so adding more won't help and may end up tipping the scales and become harmful. Blossom-end rot is more a calcium deficiency than magnesium. You can use plain yogurt mixed into the water at 2 ounces per gallon, and/or add pelletized lime and gypsum, as well as molasses (yes, black strap molasses) at 2 oz. per gallon of water.

Posted by: Bradley Cahill (1 point) Bradley Cahill
Posted: April 14, 2013

Robert commented,
I always have blossom end rot. We have lots of calcium in our soil and water is high in calcium. Are you saying to add 2 oz of lime, and 2 oz of gypsum and 2 oz of molasses to a gal of water?
about 10 years ago.

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