Outdoor plants, split skins, nutrient deficiency and late blight

Split skins – outdoor pants

If your outdoor plants were rained on last weekend, there is a good chance that some of your toms have split skins.

You may wonder why a downpour of rain causes skins to split, given that the plants receive a good watering on a regular basis – usually more water than they get from a downpour of rain!

The reason is because transpiration stops, which prevents moisture loss through the leaves, but water uptake through the roots continues for a short period.

In other words…

When leaves become wet, they are unable to release moisture, but for a few hours, water is still absorbed by a plant’s roots.

This means that pressure builds up inside the plant and tomato skins split.

Tomato split skins.

Pressure inside the plant returns to normal as a plant adjusts to wet leaves and roots reduce their uptake of moisture and nutrients.

Nutrient deficiency

Through wet periods, we often see leaves that look lighter in colour than they should be, especially in the early summer – as if they need a good feed!

The reason is often because, when wet, leaves cannot release moisture, so roots are unable to take in moisture and nutrients through their roots. Therefore, plants become nutrient deficient.

Fungal spores and blight

In August, we are trying to avoid blight – especially when it rains!

Wet leaves are vulnerable to fungal spores – especially if a plant is nutrient deficient

Because plants can become nutrient deficient (underfed) if their leaves have been wet for prolonged periods, their immune systems are also lowered with the result that plants will go down fast with blight or any other disease for that matter!

More about tomato blight here.

Indoor plants – greenhouse or polytunnel

Leaves release moisture because the air is dryer outside the leaf than inside and because of air movement – like the washing on the line dries faster in a breeze – I know because my wife told me!

A humid greenhouse will reduce transpiration (moisture loss through leaves) causing the same problems as faced by outside plants.

So it’s important to keep plenty of airflow and aeration in the greenhouse by opening the windows and doors too if necessary. It will also help avoid blossom end rot because the flow of calcium to the fruit won’t be interrupted.

There is a balance between humidity, airflow and transpiration

  • The higher the humidity the lower the transpiration and water/nutrient uptake.
  • The higher the airflow, the greater the transpiration.
  • The greater the transpiration the higher the water/nutrient uptake.

The ideal …

  • Low humidity
  • Moderate, consistent airflow
  • Moderate, consistent transpiration
  • Moderate, consistent water/nutrient uptake

Imagine trying to achieve all that growing outside!!!

If we were growing in a high tech greenhouse, we could control all these issues. Of course growing in our modest circumstances means that we can’t. However, it’s good to be aware of these aspects that effect the growth of our plants and tomatoes.

I hope all is well in your tomato garden!



6 Responses

  1. Rhys Jaggar
    | Reply


    Out of interest, a hôt dry summer has yielded the earliest ever tomatoes grown in the soil, delicious Red Alerts harvested the first days of August.

    They were sown mid April, planted out end of May and in two cases are now nestled under Winter Squash plants.

    They have barely been watered the past seven weeks and we have had only one rain episode.

    Out of more general interest, the crops thriving in a very hot dry summer akin to the Mediterranean have been Sweetcorn, winter squash, beetroot, parsnip, carrot and leek.

    I did not plan for the tomatoes to be overrun by squash, but let it happen once it was inevitable.

    It does appear a workable strategy in hot dry summers. I have my doubts it would work in a damp cool summer, but you never know.

    • Nick
      | Reply

      Hi Rhys,

      I’ve found that with temperatures so high, my cherry tomatoes are ripening and going soft very quickly – I can’t give them away fast enough!

      Given the possibility of another summer next season like this one, I may have a go at sweet peppers and chilli peppers outside.

  2. Anonymous
    | Reply

    Found this myself this year. I am very dubious about a few of my plants – Red Alert in particular – which seem very different from normal. Behaving much more like indeterminate and two of them are developing much larger fruits than they should have. I don’t think that could in any way be caused by our strange weather pattern this year. Not just on tomatoes, I have had quite a few disappointing results with flowers, for example, turning out to be an entirely different colour from stated or shown on the packet. Have bought all my seeds from big supposedly reputable companies.

    • Nick
      | Reply

      I like to save seeds from open pollinated varieties that are successful – I know they will produce a reliable crop next season.

  3. Rob
    | Reply

    Hi Nick,

    Every year for the fun of it, I grow a few indoor varieties not available from mainstream seed suppliers. I’ve grown these specialist varieties successfully in the past, but in recent years I’ve noticed considerable deterioration in the quality of seed. The seed from two such suppliers seemed especially poor this year, with outcomes similar to those of your Crimson Crush:

    • Some varieties had poor germination rate; others failed to germinate at all
    • Mixed seed – two totally different varieties in the same packet of 10 seeds
    • Inconsistent results – some plants had different shaped fruit than others, from the same seed packet
    • Some plants were vigorous – some were not, from the same seed packet
    • Some varieties that were delicious last year are tasteless this year

    Happily, I also grow popular varieties such as Sungold, Sun Cherry, Sweet Aperitif, Rosella and Sweet Million. These seeds come from mainstream suppliers and the plants they produce are always healthy and productive.

    So, will I continue to experiment with other varieties in the future? You bet I will – it’s part of the fun. But next year, I will be more selective of suppliers. I have already decided which varieties to grow in 2019!

    Thank you, Nick for your help and advice, and for your valued newsletter.

    Kind regards,


    • Nick
      | Reply

      Hi Rob,
      It looks like poor quality seeds are quite common these days – especially, as you say, from some suppliers.
      It’s good to save our own seeds from open pollinated varieties but most of the best performers are hybrids.
      I’m interested to find out if there are any new blight resistant varieties available next season.
      I’m pleased that you find the newsletter helpful.
      Kind regards,

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