At this time of the season, most of us will be looking at our plants and seeing two things :

  •     Lots of flowers and growing fruit
  •     Quite a few discoloured leaves and marks that look worrying!

Problems with tomato leaves may be divided into three groups:

  •     Problems caused by nutrient deficiency
  •     Or by stress
  •     Or by disease (and sometimes all three!)

Nutrient deficiency is very common at this time of the growing season, especially on lower leaves because plants send the nutrients they absorb to the growing tips. This means that the lower leaves sometimes go hungry, and the new growth gets all the food!

The easiest way to get nutrients into a plant is by foliar spraying and usually improves the colour of lower leaves.

Yellowing leaves can be removed up to the first truss, and higher as each truss begins to ripen.

The most common sign of stress is leaf curl on top growth.
Leaf curl on the lower part of a plant is usually OK and some varieties curl their lower leaves by default.

Stress can be caused by wide temperature fluctuations or over watering and a lot of other things too – check that there is good drainage because a build up of water at the bottom of a pot or grow bag can cause all sorts of problems!

Plants usually settle down after a period of stress (two or three weeks) and you’ll probably still get a good crop of tomatoes.

The third cause is disease, but with tomato plants, once a disease has taken hold, it can be very difficult or impossible to cure.

Fungal diseases are normally the most common – especially in a wet UK – and can affect the stems, leaves and lastly the fruit. Most are incurable but can be contained and stopped from spreading to other tomato plants.

The best method is to spray with a fungicide like Systhane (Dithane 945 is being replaced by Systhane), and this will help prevent the spread but probably not cure the disease.
Touching leaves, from plant to plant, can also spread disease and so can using the same blade when removing side shoots etc.

After these past few months of wet weather, I shall be spraying by default. Many gardeners and allotment holders have lost their tomato plants because of blight. If you are growing organically in a wet region, it is almost essential to grow under cover to get good results.

Tomato Taste
It is a very satisfying moment when biting into your first home-grown tomato of the season!
Every variety has is own particular characteristics where taste is concerned. Some are on the acidic side, others are on the sweet side of the taste scale and others are well balanced – somewhere in the middle.

Watery Taste
Sometimes the taste of tomatoes can be disappointing and considered “watery”. This usually happens when plants have been over-watered and under-fed. Plants can only absorb the food (nutrients) they need with water and if the food has been watered-down (diluted by over-watering) less nutrients are absorbed.

It’s a bit like calcium and Blossom End Rot – you can’t get nutrients into a tomato if it’s already fully grown.
Unlike the leaves, that can perspire (transpire) so that water and nutrients can be replaced, tomatoes can’t do this, so what goes in stays in and when a tomato reaches its full size, that’s it.

Apart from being fed correctly, magnesium is said to increase taste.

Has anyone had experience of magnesium increasing the flavour of their tomatoes?

Would love to hear your view!

6 Responses

  1. Rhys Jaggar
    | Reply

    No science on magnesium and taste, but I can say that my Tumbler plant, like all my tomatoes, this year has been fed magnesium twice so far: once 6 weeks after going into its final pot (guessing time when nutrients start to run out) and once 4 weeks later. They are all due another round at the beginning of August.

    The Tumbler fruit have been very tasty. Alicante and Shirley are ripening now so we shall see what has happened.

    It was also noticeable that the plants looked much healthier in the 5 days after being fed magnesium, suggesting that feeding them a bit of magnesium helps. I used 2 teaspoons of Epsom Salts (magnesium sulphate) in one gallon of rain water which was shared between 10 plants in 10 to 12 inch pots. This was a guesstimate of what was recommended as a dilution on the packet as I don’t have weighing scales that go down as low as necessary.

    Definitely the case that Alicante requires more water than Shirleys. Or if they don’t, they are more sensitive in response to starting to dry out (champion droopers which recover within a few hours of being topped up).

    The only other comment I have is that the size of final pot may make difference after 3 trusses. All my plants in 10 inch pots have formed 3 excellent trusses with Shirleys, but are very variable on trusses 4/5. Blossom drop, variable growth rate of set fruit etc. The one plant in a 12 inch pot has much bigger 4th and 5th trusses which have flowered very well and look like producing more fruit.

    I have also had one truss on a few Shirley plants start to half break under the weight of tomatoes. I’m leaving them as they are, although whether they will grow more or ripen like that I don’t know.

    I’m assuming that’s just a good thing rather that some dietary insufficiency. Live and learn, anyway.

    • Nick
      | Reply

      Hi Rhys,
      Thanks for your comprehensive comments as always – they are very helpful and give us plenty of food for thought!

  2. Buster
    | Reply

    Just wondering about the “give it a drop of widdle” effect on flavour!
    It was used a lot years ago as a general fertilizer.
    And how much does the type of basic soil /additives affect the flavour.
    I’m starting some trials from today.
    Thanks B

    • Nick
      | Reply

      Hi Buster,
      Will look forward to the results of your trials if you don’t mind sharing them.

  3. Mark D
    | Reply

    An interesting question about magnesium. I think I’ll get some epsom salts (magnesium sulphate) and try a little experiment, feeding some plants and not others, to see what difference there might be.

    • Nick
      | Reply

      Hi Mark,
      Always interesting to do a split test – will look forward to your results if you don’t mind sharing them.

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