The question posed in last week’s newsletter was, “why do tomatoes that are grown outdoors split when it rains?” and it has produced some good comments.

Tomato Split

To those who have been contacted, you will receive Red Alert (bush) and Stupice (tall) seeds and they should arrive this coming week.

The traditional answer of dry soil followed by too much water is generally correct, especially for greenhouse grown tomatoes. Roy gave us a list (in the comments of last week’s newsletter), of good reasons why tomatoes split. Both Roy and Nic also touched on temperature, this is another variable to be taken into account.

Here’s my answer to “why do tomatoes that are grown outdoors split when it rains?”.

Tomato Plants are similar to humans in some ways …

  • We have veins, blood and blood pressure.
  • Tomato plants have veins, water and water pressure.

Tomato leaves are very absorbent and when it rains, plants take on moisture through their leaves and roots, creating maximum pressure within their system. Therefore, ripe tomatoes become fully pressurized like a balloon filled to the maximum.

However, rain falling on the tomato skins lowers the skin temperature slightly, causing the skins to contract – the skins then split.

Even if outdoor plants are watered regularly so that their soil remains moist, a downpour of rain can increase the pressure inside ripe tomatoes and shrink the outside skins at the same time!

Fortunately, as soon as the first few toms split, the pressure inside a plant’s system drops slightly and the rest of the tomatoes are out of danger!

In my experience, varieties that contain a lot of juice such as Sungold and Black Cherry split more easily than those that contain less moisture – Roma is a good example and great on the barbecue because of its fleshy qualities rather than juicy qualities.

Black Cherry Tomato

Black Cherry is a lovely juicy variety and great for saving seeds!

Putting warm tomatoes in the fridge can also cause the same affect – the skins shrink faster than the inside because of the sudden cold air and so they sometimes split, as suggested by Avril.

Keeping Leaves Dry
The problem of splitting skins brings us back to one of the biggest “do’s” in tomato growing – keep the rain off leaves and fruit if possible.

I have plants outside exposed to rain, plants outside but sheltered from rain and plants in a greenhouse. This gives me the benefit of experiencing the results of different growing conditions on the varieties I grow.

Choose a Mix of Varieties
As suggested in a previous newsletter, this gives the advantage of being able to contrast and compare and often reach a conclusion and find an answer to a problem when things go wrong – as they will every season!

When considering which varieties to grow next season, try choosing tall and bush varieties, and also ones that are early to mature. Also, devising a way to shelter your outdoor plants from rain will increase the chance of success and lessen the chance for disease – aka – Tomato Blight!

Bush Varieties
Bush varieties have many advantages but one supposed disadvantage is that all the tomatoes fruit within a short period.

I say “supposed” because I have two Red Alert plants that started producing ripe fruit back in the middle of June and they are still producing ripe fruit at the end of September.

Also, of all the varieties I’ve ever grown, the cherry/bush varieties are among the best tasting and I would recommend Red Alert and Maskotka along with Tumbling Tom to everyone for next season.

Tumbling Tom YellowThis one plant has produced a lot of tomatoes and is still going strong – it’s under cover!

There is one yellow Tumbling Tom plant in the greenhouse (above) that has produced well over two hundred tomatoes so far this season! They may not be big in size, but if I were to weigh them all, I’m sure that this one plant could compete with many of the larger varieties in the weight produced.

One disadvantage with bush varieties is that their branches tend to break away from the main central stem because of the weight of tomatoes.

Split Tomato BranchThe split branches are still producing ripe tomatoes on this Red Alert plant!

Usually, the plant can still function and water/nutrients will still pass through to the leaves and fruit. This plant has been in this condition for about two months but is still producing well.

Next week is the last newsletter of the season!

Please leave a comment below if you would like to.

Best wishes,

20 Responses

  1. Tuly
    | Reply

    Its a tricky bsienuss growing in the winter in a g/house, you have to keep it heated for a start and is really only good for starting seedlings off not producing veg or fruit as theres not enough light this time of year, but from spring through to summer is the best time to grow the likes of tomatos and cucumbers or whatever you want to grow. I wouldnt try to grow anything unless your going to heat the g/house every day and night and all you can put in is leeks or onions or some winter lettuce put thats just to start them off so there ready for spring time to go into the ground.

  2. Wilson Baskett
    | Reply

    Dear Nick.
    I have just grown for the 1st time tomatoes. Well anything for a matter of fact and really got the bug! I read your news letters and going to take on all the advice for growing next year. Hopefully will have a better growing season….

  3. Nic
    | Reply

    Many thanks for your site – so interesting, informative and so nice to find a human at the end of a computer!
    Keep up the good work – really looking forward to next season and thank you for the seeds!
    My crop was largely lost to blight this year but now with what I have learned I am going to try different varieties and ways to grow. Hanging baskets sounds fun!
    Happy Chutney days everyone!

    • Cesar
      | Reply

      You don’t say where you live, and that can make a BIG difference in how much sucsecs you would have growing in a greenhouse in winter. I live in Minnesota, where of course it gets really cold and days are short. I worked in a hydroponic greenhouse here, and we grew only greens, lettuces, kale, the winter. Spring through fall we grew tomatoes, basil, peppers and other greens, but they just won’t grow in the winter, there isn’t enough light. It also costs a lot of money to heat a greenhouse in winter, so do your homework before you make a decision. I should say that you can add supplemental lighting to a greenhouse in winter, but again it is very expensive.

  4. KEVIN
    | Reply


  5. David Jones
    | Reply

    Hi Nick, thanks for providing such a useful website.
    This was my first year of both having a greenhouse and growing tomatoes. I came across your site when looking for advice on watering, the information provided was extremely helpful. I have been moderately successful with Beefheart, Alicante and Gardeners Delight purchased from a local diy warehouse but more successful with Roma and Gardeners Delight plants that were given to me by a local grower, proving that source is sometimes as important as type. I grew all my plants as cordons (not knowing any better) only learning later that some could have been grown outdoors as bush plants. Once again thanks for the website, I have taken your advice onboard and am looking forward to next spring and the start of a new tomato growing season.

  6. JaneB
    | Reply

    Thanks for walking me through the first year og tomato growing, mixed results but enjoyed growing them and will try again next year.
    Thanks again for all the advice.

  7. Bill Hadden
    | Reply

    Hi Nick,
    As a recent visitor to your website, let me say thanks for all the
    practical and useful info you have provided over the season. I look forward
    to next year. Hopefully a better summer at least ! This year has been the worst ever for toms in Northern Scotland ! Regards, Bill Hadden

  8. Janis
    | Reply

    Hi Nick

    thanks for all the support, info and encouragement for the past two seasons. I especially enjoy the grow-along bit!

    Have had a great tom year, and was surprised to see Gardeners World last night talking about the opposite… Am busy preserving as many as possible by following means:

    1) eating!!
    2) my balsamic tomatoes – OMG how gorgeous they are. Great for using odd shapes, softies, even split toms. Wash them, cut them in half around the equator (!), put in a roasting pan with some good olive oil, balsamic vinegar, seasoning and I have some fresh basil and thyme on hand too. Don’t forget some sugar. Roll them all around to coat them, cook for around an hour and a half on 160C. They are ready to serve – lovely hot as a side veg dish with chicken or fish, or steak, or lamb…. ok with anything. If any are left, allow to cool and they will store for a week or two in the fridge. Lovely for a quick panini…
    3) freezing, this is new this year for me. I have been advised to wash them, hull them to remove the stem scar, place them in a layer in a ziplock bag and freeze. No need to blanche or dice. Remember to remove as much air as possible but leave some room for expansion as the water in them will make them expand a little on freezing. Or, you can freeze them individually on a tray then store them in a ziplock bag. Either way they will be great for stews, soups, etc in the winter. They should store for up to one year in the freezer.

    Kindest regards and, until next March, happy tomato eating

    • Nic
      | Reply

      Ooh, nice yummy ideas there, thanks!

  9. douglas
    | Reply

    Ive only been a member a few weeks but allready have learnt quite a bit from the newsletters.Iwish Id joined at beginning of growing season ,rather than the end.
    Im toying with trying some heirloom tomatoes next year,not sure which variety to use living in not exactly a tropical place! I would be glad of any suggestions.

  10. phil
    | Reply

    Thanks for great site,already looking forward to next years tips,Tigerelle,red pear,shirley and sungold were our favourites this year.

  11. Jan Garbett
    | Reply

    On this, my second year of attempting to grow tomato plants, I have had such a learning curve thanks to your help, and needless to say, a huge increase in harvest. I can’t wait for the next season. I think I’ll try beef toms if I can find them soon enough, and plant Shirley again – tasty.
    Again, a big thanks to you Nick for all your advise.

  12. Roy
    | Reply

    Hi Nick
    Many thanks for all the info during the summer.
    Looking forward to to next year.

    • Nick
      | Reply

      Hi Roy,
      You’re welcome and thanks for your helpful comments this season!

  13. william forsyth
    | Reply

    Well nick, sorry to hear next week is the last newsletter, look forward to receiving it every month. Not a good season for me this year in Scotland, to much rain not enough sun. This year I tried tigrella not very good, what would you recommend for next year in the greenhouse keep up the good work and all the best for the coming year.
    cheers, Willie

    • Nick
      | Reply

      Hi Willie,
      I would try the short season varieties such as Stupice and Glacier (tall) and Red Alert and Latah (bush).
      From the emails I’ve received, I think that most gardeners in Scotland have struggled this season to get a good crop.
      All the best to you too!

  14. Lyn Say
    | Reply

    I have so enjoyed your guiding hand. I have grown my tomatoes in hanging baskets have a wonderful crop still picking every day.
    One of the dogs started taking them off the plant but am glad to say they did not seem quite her taste!
    Thankyou for all your guidance

    • Nick
      | Reply

      Hi Lyn,
      I’m very pleased that you have found the website helpful.
      We used to have a Yorkshire Terrior who loved tomatoes but she always spit out the skin!
      Best wishes,

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