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Epsom salt fertiliser for tomatoes

Updated: October 2026

You are looking at a tomato in a pot, a grow bag or a greenhouse, and either the older leaves are yellow between the veins or the bottom of a fruit has gone black. Epsom salt fertiliser for tomatoes fits the first of those and not the second. This page stays on one crop. Prices below are the amazon.co.uk product data from 19 October 2026. The clashes across the twelve listings sit on the [Epsom salt fertiliser comparison](/hub/fertiliser-soil-and-bark-mulch/epsom-salt-fertiliser). Products Compared did not run a laboratory trial. A qualifying purchase can earn us a commission at no extra cost to you.

You are looking at a tomato in a pot, a grow bag or a greenhouse, and either the older leaves are yellow between the veins or the bottom of a fruit has gone black.

Our top picks

Westland Westland Epsom salts 1.5 kg

Best overall

Westland Westland Epsom salts 1.5 kg
8.2/10about £7.50
View offer
Vitax Vitax Epsom salts 1.25 kg

Rank 2

Vitax Vitax Epsom salts 1.25 kg
8.9/10about £8.50
View offer
Hexeal Hexeal Epsom salt 5 kg

Alternative

Hexeal Hexeal Epsom salt 5 kg
7.7/10about £11.40
View offer
On this page
  1. 1.Older leaves, not the fruit end
  2. 2.Tomato feed can be the cause
  3. 3.What to do if the pattern fits
  4. 4.Listings that name tomatoes

Older leaves, not the fruit end

Magnesium on a tomato shows on the older leaves: yellow between the veins, sometimes reddish brown, while the veins stay greener. The Royal Horticultural Society names tomatoes for that pattern. The youngest leaves turning yellow first are the iron pattern. If only the older leaves are mottled and the plant is otherwise cropping, the RHS says there is often no cause for concern. The black, sunken end of a fruit is blossom end rot. The RHS describes it as a lack of calcium in the fruit, usually because water supply was uneven, and it is worst in pots and growing bags. Magnesium sulphate does not put calcium into the fruit.

Tomato feed can be the cause

High-potassium feeds make the plant take up potassium in preference to magnesium. The RHS names tomato fertilisers among the high-potash products that can lead to the deficiency. If you have been doubling the scoop for more fruit, the yellow older leaves can be the result of that scoop. Ease the tomato feed back to the rate on its own label. Epsom salt remains 0–0–0 plus magnesium on the RHS fertiliser page, so it does not replace the nitrogen and potassium the plant still needs.
Westland Westland Epsom salts 1.5 kg

Testsieger

Westland Westland Epsom salts 1.5 kg
8.2/10about £7.50
View offer

What to do if the pattern fits

Use the rates on how to use Epsom salt fertiliser, not a second method invented for tomatoes. When the pack has no grams, the RHS figures are 30 g per square metre on light soil or 20 g per litre as a foliar spray in dull weather. Do not spray in sun. One grow bag is not a square metre. If your Vitax carton prints 20 g per litre, that matches the RHS foliar figure and does not match 70 g per square metre. Westland’s mixing field is 1:0:0. Follow the carton you open. A tablespoon on a Hexeal bullet is not 20 g until you weigh it.

Listings that name tomatoes

Westland B001P3SMQ0, £7.50, puts tomatoes in the target-species field. It is granules, 4.6 from 1,463. The amazon page does not print a gram rate. Item weight is 1.44 kg against a 1.5 kg title. Vitax B003MPGFIG, £8.50, names tomatoes and houseplants and prints 20g/l. It is 4.5 from 675. Item weight is 500 g against a 1.25 kg title. Hexeal’s garden bullet names tomatoes, with 1–2 tablespoons in around 4.5 litres. Those rows are Beauty bath salts, and the 2.5 kg and 5 kg files share one review line. None of these amazon rows prints an MgO percentage.

Common questions

Which tomato leaves should be yellow if this is magnesium?
The older leaves, yellow between the veins, sometimes reddish brown, with greener veins. The RHS names that pattern for magnesium and names tomatoes. If the damage is only there, the same RHS tomato-leaf page says there is often no cause for concern. You act when the pattern is strong or a high-potash feed is the likely push, not because one lower leaf faded.
My young leaves are yellow. Is that the same thing?
No. The RHS chlorosis page treats yellowing that starts on the youngest leaves as the iron pattern. Magnesium and manganese tend to start on older leaves. Epsom salt is the wrong first buy for a yellow tip. Check the feed and the pH of the compost before you add magnesium the plant may not be short of.
Will Epsom salt stop blossom end rot?
No. Blossom end rot is a shortage of calcium in the fruit, usually from uneven watering, and it is worst in pots and growing bags. The RHS does not list magnesium sulphate as the cure. Keep the bag evenly moist. Do not treat a black fruit end as a reason to dissolve a tub of salts.
I already use tomato feed. Do I add more?
Often the feed is the push, not the missing piece. High-potash tomato fertiliser can make the plant take up potassium ahead of magnesium. Use the tomato feed as directed, and do not double it. A foliar magnesium spray is the add-on when the older-leaf pattern is already there. It does not replace the tomato feed, because this salt supplies no nitrogen, phosphorus or potassium.
The RHS says older leaves alone are no cause for concern. Do I still spray?
Not automatically. If the mottling is limited to older leaves and the plant is growing and fruiting, you can leave it, water evenly, and keep the tomato feed at the label rate. Spray when the yellowing between the veins is obvious and you have been using a high-potash feed heavily. The two sentences are a condition, not a contradiction.
Is a grow bag more likely to show this than border soil?
Yes, in the usual UK setup. Pots and bags have a small root volume, dry out faster, and get a concentrated tomato feed. The RHS flags pots and growing bags for blossom end rot for the water reason, and high-potash feeds for the magnesium reason. Border soil that is only slightly mottled on the lowest leaves is the case the RHS tells you not to panic about.
Can the salt sweeten the fruit?
Do not expect that. These listings do not print a sweetness claim you can rely on, and this comparison does not make one. One stray review is not a result. Magnesium corrects a leaf pattern when the pattern fits. It is not a flavour treatment, and it will not repair a fruit that already has blossom end rot.

Related pages

Epsom salt fertiliser buying guide

Best Epsom salt fertiliser

Garden or food-grade Epsom salt

Epsom salt fertiliser

How to use Epsom salt fertiliser on soil or leaves

Sources

Public UK sources from the research digest, used for this page in October 2026. Prices, stars and review counts are from the twelve amazon.co.uk listings captured on 19 October 2026. No listing here prints a magnesium oxide percentage. A shared review file is not two garden tests. This is not a laboratory test and not an RHS trial of these packs.

  1. RHS, Nutrient deficiencies (retrieved 19 October 2026)
  2. RHS, Fertilisers (retrieved 19 October 2026)
  3. RHS, Blossom end rot (retrieved 19 October 2026)
  4. GOV.UK, Manufacturing and marketing fertilisers (retrieved 19 October 2026)
  5. Regulation (EC) No 2003/2003 article 9 (retrieved 19 October 2026)
  6. Regulation (EC) No 889/2008 Annex I (retrieved 19 October 2026)
  7. Fertilisers Regulations 1991, Schedule 2 (retrieved 19 October 2026)
  8. Soil Association, organic salt clarification, 10 September 2024 (retrieved 19 October 2026)