How to Identify and Correct Tomato Nutrient Deficiencies

, written by Jeremy Dore gb flag

Tomato nutrient deficiency

This week I noticed that two of my tomato plants had yellow-brown leaves at the bottom and certainly didn’t look as perky as I expected given the attention I have been giving them. Admittedly these were two of the many surplus plants I raised from seed and so they ended up outdoors in rather poor soil usually reserved for less fussy plants. But I love tomatoes and can’t bear to see plants die, so out came my reference books to find out the cause.

Just as we need a full range of vitamins from a wide variety of food, so plants need essential minerals to survive and grow well. There are a whole range of these which are usually supplied by rich soil and compost. The main ones are:

  • Nitrogen (N): this is essential for plant cell growth and chlorophyll – used in leaves and all the green parts of the plant – and is therefore essential for all vegetables. In particular vegetables grown for their leaves need a plentiful supply. Lack of nitrogen results in slow or spindly growth and leaves can yellow, often the older ones first.
  • Phosphorus (P): essential for healthy roots and also for fruit to ripen. Lack of phosphorus shows up when growth is poor, leaves begin to have a blue/green tint or fall off and fruit and flowers are disappointingly small or late.
  • Potassium (K): vital for flower and fruit growth. When lacking, fruiting plants are unproductive and older leaves can show signs of ‘scorching’, turning brownish and rolling up inwards and downwards.
  • Magnesium (Mg): A lack of magnesium shows up as discolouring of the leaves between the veins: from a healthy green to a pale yellow and eventually brown – a sort of mottled appearance called ‘intervein chlorosis’.
  • Calcium (Ca): A lack of calcium shows up as young leaves curling inwards and lacking colour, and is often a problem in acid soils. ‘Blossom end rot’ in tomatoes is caused by this condition.
  • Many other nutrients – Zinc, Copper, Manganese, Iron, Sulphur and Boron are also required in small quantities. Several of these can also give rise to intervein chlorosis (see Magnesium above)
Liquid feed

It seemed most likely to me that my tomatoes were suffering from magnesium deficiency – it’s a common problem with tomatoes and potatoes, especially on light sandy soils such as mine. Now, the traditional agricultural approach to deficiencies is to identify the missing mineral and spread the corresponding fertiliser to deal with the problem, or an NPK one containing the top three minerals listed above. I’m not keen on taking that approach because it goes against the organic principles I follow when gardening. Plants need a full range of nutrients, preferably from natural sources, and overdosing them on one (even if it’s in response to a deficiency) can often reduce the availability of others. So for organic alternatives the following are good:

  • Seaweed Liquid Feed: Quite expensive but full of all the required nutrients, particularly potassium which is great as tomato plants mature. You simply dilute a capful in a watering can, best applied to the leaves (a ‘foliar feed’) once a week, where it is better absorbed than being washed into the soil
  • Comfrey Leaf Tea: Comfrey is a great plant to have – it grows quickly bringing up nutrients from deep down in the soil and its leaves can be cut back, packed into a container with water (and perhaps some urine) to make a foul-smelling liquid that is rich in almost everything that developing plants require.  It is then diluted like seaweed feed. Just make sure you place comfrey plants away from your main beds (shade is fine) as it spreads easily and is almost impossible to get rid of.
  • Leaf Feeds: useful for green crops that are harvested for their leaves as they contain plenty of nitrogen. Borage tea is made in a similar way to comfrey and works well for hungry plants. Urine can also be used, well diluted, or at least added to the compost heap once in a while.
  • Mulches: - see my recent GrowBlog article about this – well-rotted compost or comfrey leaves make an excellent mulch which gradually releases nutrients to the plant.
Yellowed leaves on a tomato plant

Of course, it’s worth mentioning that vegetables shouldn’t be harvested for a few days after a feed has been applied and even if it is organic they should be washed well.

Prevention is better than cure – for most areas of my garden the solution is to mix in plenty of organic compost a little while before planting. But I still rely on foliar feeds such as seaweed and I’m convinced my plants look better for it and produce far more. Those tomato plants should be recovering in no time…

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Show Comments


"you say urine ! who`s urine ?"
T on Saturday 14 June 2008
"Well, traditionally the gardener's, though I don't suppose it matters whose! It's very rich in Nitrogen and a whole range of nutrients and works well as a compost activator (to get the decomposition going)! You'll find a number of well-known gardeners recommending it, such as Bob Flowerdew, though only if you're not taking antibiotics or hormone treatments etc."
Jeremy Dore on Monday 16 June 2008
"Jeremy, I'm thinking of setting up a Bokashi bucket to allow me to add cooked food to my sealed composter. I looked on the net and it appears that the system basically pickles the cooked food so that it won't smell and attract vermin. I read that it breaks down very quickly when added to a compost heap and speeds up general composting. It uses EM liquid which is supposed to add beneficial bacteria and allow plants to take up nutrients more easily. Has anybody tried this system and what sort of experience have thay had?"
mrsmiggins on Saturday 21 June 2008
"Should I cut the leaves of if they are like the picture above?"
Garden on Tuesday 24 June 2008
"You only need to cut off leaves if there's an infection (like blight which is very unlikely this early in the year.)So I would leave them on, since it's just indicating a mineral deficiency."
Jeremy Dore on Tuesday 24 June 2008
"Two quick comments. As my daughter is potty training I have a ready supply of urine which gets added to the compost heap. Also we use "worm wee" from our wormery as a plant feed, we have had amazing tomatoes our of grow bags by this method. It must be diluted though as it is very strong, infact it works temporarily as a weed killer if you don't"
anna on Thursday 17 July 2008
"Yes, wormery liquid is another excellent source of nutrients - thanks for mentioning these!"
Jeremy Dore on Friday 18 July 2008
"I've grown comfrey for years and use it ,as you suggest, to make a liquid fertilizer. Bocking No.14 is a variety which stays in one place. I got mine, years ago, from HDRA. It's a great tomato food"
Iris Holdom on Tuesday 2 June 2009
"Im starting to grow my own vegatables and i think i have a deficiency in my tomatoes. I would like to remain organic while adding anything missing to each veg. I own several pets and im struggling to find anything safe to use on my garden. I also feed alot of my greens to my rabbits, so its essential that anything i add isnt toxic. Can you help? "
Louise on Wednesday 9 September 2009
"@Louise, the liquid seaweed feed mentioned in this article is fully organic and safe, so I would recommend you use this watered onto the leaves. It is best to give it a couple of days after application before you eat any produce it has been used on and the same would probably apply to the pets who won't like the smell of it when it has just been applied to leaves."
Jeremy Dore on Thursday 10 September 2009
"What a cool sight,I was looking for ways to use Borage as a tea fertilizer.Its such a great sight so helpful."
Shon yde on Tuesday 2 November 2010
"This is a very helpful post, i hope this really helps me to complete my project."
Oom yung Doe on Saturday 19 February 2011
"Out of interest, for magnesium deficiency I found a website that recommends spraying leaves with a mixture of 1 pint water to half ounce of Epsom Salts, daily for about a week."
C Kennedy on Wednesday 13 July 2011
"who is HDRA in the comfrey coment"
loraine williams on Tuesday 4 April 2017
"HDRA is the Henry Doubleday Research Association, I just looked it up to see if it still exists and it's now known as Garden Organic."
Iris Holdom on Wednesday 5 April 2017
"You could have safely used Epsom salts (magnesium sulphate) for your deficiency. It is a mined, natural product. Seaweed solution is fine, but supplies very little nitrogen. I spray my tomatoes with a foliar spray - 10 gms Epsom salts per litre - every two weeks to prevent a deficiency."
Julie on Wednesday 2 January 2019
"I don't have comfrey planted and can't get a hold of a live plant to make the tea. Will making a tea from dried, organic comfrey leaves work as well?"
Kat on Tuesday 7 May 2019
"How do you make comfrey liquid?"
Tim Ross on Tuesday 25 August 2020
"I have tomatoes that ripe but the stem end of the fruit is yellow and hard. This yellow part extends into the fruit. So the tomato is part lovely and ripe and the part hard and yellow"
John on Wednesday 10 February 2021

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