This is about the time of the season when ripe tomatoes begin to split. If the problem is severe, it’s possible to have an entire truss of tomatoes with split skins!

We know that tomato plants lose a lot of moisture (through transpiration) when the weather is hot and they need a lot of water to prevent them from wilting. They also need to keep fully pressurised – a bit like a bicycle tyre, pumped-up (turgid). Although the amount of pressure in a plant varies, even from morning to evening, the variation is usually slight and plants cope OK.

Tomato Split
Split skins caused by a sharp rise in pressure.

However, in hot weather, when plants are using and losing a lot of moisture, the pressure variation can be much wider causing tomato skins to burst when pressure suddenly increases. In the other extreme, tomato skins can become wrinkly as moisture is diverted from the tomatoes back to the stem and leaves of a plant.

Although the later case is unusual, it does happen in hot conditions, when plant are struggling to keep turgid, and mainly effects tomatoes with more moisture content.

Watering frequency
For outside tomatoes, a sudden downpour of rain is often the cause of excess moisture, pressure and split skins.
For tomatoes grown under cover, the cause of split skins is usually infrequent watering. The watering frequency required to avoid the problem depends on the amount of moisture the growing medium, usually soil, can hold – as well as the temperature of course.

A cause of blossom end rot
When water availability runs low, moisture that would normally go to the fruit is diverted back to the plant in order to keep it pressurised (turgid). When this happens calcium and other nutrients are withheld from the fruit and blossom end rot is likely to occur.

So wide swings in moisture availability can cause BER as well as split fruit.

Double stemming
One way to help reduce the problem is to grow two main stems on each plant – especially on varieties prone to splitting. This has the advantage of having a greater internal capacity and therefore plants are less prone to sharp rises in internal pressure that split ripe fruit.

I found this to be particularly useful when growing Sungold this season.

Another issue when avoiding split skins is container size
For example, basic potting compost in a 10 litre pot will need watering more frequently than a plant growing in a 50/50 compost and perlite mix in the same size pot. The plant in the basic potting compost will also be more vulnerable to split skins and BER.

The 50/50 soil and perlite mix can hold more water, will take longer to dry out, and consequently, needs watering less often. As just mentioned, the tomatoes grown in it will be less vulnerable to BER and split skins – not to mention other water stress problems.

Are bigger pots better?
Am I suggesting that bigger pots with added perlite are better … no … I’m suggesting that bigger pots with a medium that holds plenty of moisture are easier to manage. If you have a system of watering, such as a reservoir beneath a pot, the pot size and ability of the soil etc. to hold moisture is less critical.

Rockwool as an example
An extreme example is a 3 inch rockwool block. I grow dwarf varieties such as Vilma, Micro Tom and Heartbreaker, in my porch, in 3×3 inch rockwool blocks. The size of the growing area isn’t important if the medium (in this case rockwool) is watered and fed correctly.

Rockwool holds a lot of moisture as well as air and it looks a bit like loft insulation. I would encourage everyone to have a go at growing a small variety in a rockwool block on the windowsill next season – it’s a great learning experience!

To Sum Up

If you suffer from split skins or blossom end rot here are a few tips for next season.

  • The most important point is to make sure that the soil, or whatever you are growing your plants in, doesn’t fully dry out.
  • Larger pots are safer – they hold more moisture and take longer to dry out. Larger pots with added perlite etc. are even safer!
  • Smallish pots with economy potting compost are the worst combination.
  • Medium size pots over a reservoir with perlite are very good – the reservoir provides a constant water supply and the perlite provides plenty of oxygen.

I hope that you’re ripe tomatoes haven’t started to split.


16 Responses

  1. Conor McGovern
    | Reply

    Hi Nick,

    I had a good few split sun golds in my indoor autopots this year.
    Seemed to happen when raining outside – maybe atmospheric moisture?
    Will try your twin vine trick next year.
    Sung old ran outta steam after 6 trusses so having started harvest mid-June, I have the first plants removed and have second set in autopots with fruit swelling – might be too late to ripen in Dublin this year but I know now to have a second crop coming on earlier next year.
    Also have indigo rose growing and they have taken FOREVER to ripen into a poor flavour. They are a great talking point – whole trusses of 8-ball pool balls – but not growing them again.even with zero splitting.
    Gardeners delights have worked well for me – strong steady production, no splitting.
    Black Russians and stupice were good. I would try stupice again – good taste, no splitting, but not vigorous the way I grew them. Black Russians produced well but beef toms don’t fit well for our eating patterns – so cherries are my favourite.
    Thanks again for another seasons excellent newsletters – always super reading for weekend mornings.

    • Nick
      | Reply

      Hi Conor,
      I’m having the same experience with Indigo Rose – they look great but are taking ages to ripen!
      I’m pleased that you enjoy the newsletters.

  2. Bill Hadden
    | Reply

    Hi Nick, you beat me to it ! I was about to contact you re split tomatoes. In my case Gardeners Delight. Thanks for
    all the info. Every year my tomatoes lack the nice shiny appearance of ripe fruit, very dull, although they taste ok.
    This year I grew Shirley, Ailsa Craig and Gardeners Delight. The former 2 varieties very dull, the latter ok. They
    are grown in 10 litre pots in Miracle grow and growbag compost, 50%50, and fed with Dobbies feed. Am I doing something wrong. I will look forward to your comments.
    Thanks, Bill.

    • Nick
      | Reply

      Hi Bill,
      I sometimes get trusses with tomatoes that aren’t as shiny red as they should be. Potassium and magnesium are the nutrients responsible for a good “finish” with plenty of lycopene under the skin, although maybe it’s the skin itself that is the problem. To be honest I’m not sure but something I will look into.

  3. Buster
    | Reply

    Found that ‘Amateur’ produced well but tended to split in the hot weather. Other varieties fine & still going.
    Just wondered if some tom varieties retain more water & heat expansion bursts the skin.


    • Nick
      | Reply

      Hi Buster,
      That’s a good point … when temperatures rise the water content will expand and burst the skins. Also, for outdoor tomatoes when it rains, the skins will probably contract too.

  4. michael Johnson.
    | Reply

    Just as a matter of pure interest- did you know that the world record giant tomato has just been broken in the U>S>A, after 28 years with the old record of 7.35 lbs, the new world record is now a whopping monster of
    8.40 lbs, and smashed the world record to smitherines, I am quitye excited by it-new challenges and all that 🙂

    • Nick
      | Reply

      Hi Michael,
      I didn’t know about the world record … do you know which variety it was – it would be fun to try and grow a whopper next season too!

      • michael Johnson.
        | Reply

        Hi-Nick, it was a cross derived from the original (Big Zac) tomato, crossed and re-selected over several years, funnily enough it was grown on a plant only three foot high, the reason for this was because the plant which is usually about 5-6 foot tall, put all it’s energies into the big tomato first, it was a Mega bloom comprising of six tomatoes fused together into one, on a one inch wide ribbon stalk.
        If I am lucky enough to obtain any seeds from Dan Mcoy this coming winter, I will send you a few to try 🙂 I already have seeds for the current french champions (Boudyo) which came out of a tomato weighing in at 6.86lb, so far I have tomatoes of around 4lb + this season, If I fail to get the McCoy’s I can send you some of those instead, the whole essence to obtaining a giant is to try to pollinate any fused megablooms on the first bottom truss, which is when they usually form.

        • Nick
          | Reply

          Thanks Michael … that’s very kind of you!

      • michael Johnson.
        | Reply

        here’s the you tube video of it, new world record 2014 🙂

  5. Steve
    | Reply

    Hi Nick

    In your summary you refer to ‘Medium size pots over a reservoir with perlite’.

    Have you covered this in more details in one of your news letters? If not could you suggest a reference for

    further reading as I would like to have a go next season.

    Many thanks for all the advice etc during the year!


  6. Valerie
    | Reply

    Good morning Nick.Saturday breakfast is always interesting,especially since my husband has weekly cooked breakfast with tomatoes!
    Your comments on BER and split skins are very pertinent in my family.A few observations .Gardeners Delight suffered badly from BER! Black Cherry from Mark RS have had none and are romping away.Saved seed from Momeymakey,after an early attack of BER are producing large tomatoes,almost beefsteak and my favourites ,
    Golden Sunrise again saved seeds,have produced early tasty and even sized fruit.
    I have just started saving seeds from some micro toms which came from my daughter.No idea of name.
    Finally I have observed that Dirt Pots are very thirsty .Next year I shall use the 11ltr but with added perlite.
    I don’t think I am an obsessive yet!

    • Nick
      | Reply

      Hi Valerie,
      A cooked breakfast with your own tomatoes is one of the treats of the summer – I love the sizzling sound as they go into the frying pan!
      I too have found that my medium varieties have been bigger than usual this season – no doubt the weather has helped. Dirt pots, and fabric pots generally, are one of the best containers for tomatoes and perlite in the mix will make them even better.

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