Feeding, Watering, Pruning and Heat Stress

At this time of the tomato growing season, the most visited pages on the website are concerned with feeding, watering, pruning and tomato problems.

Like most subjects, we can make it as complicated or as simple as we wish to. Perhaps if we were supplying Sainsbury’s, or entering a contest, we would need to get the very most from our plants and optimize in every aspect of tomato growing.

However, given that most of us are probably growing for fun and the great taste of home-grown tomatoes for our own kitchen, here is the straightforward and time saving approach!

For tomatoes grown in containers and grow bags.


  • In warm weather, feed half strength every third day.
  • The idea is to feed little and often rather than a lot once a week.
  • If your large pots/containers are stood in trays, water in tray – feed/water in soil.


  • The idea is to keep the whole soil area just moist – impossible really!
  • The best way is to have the soil wet in the morning and dryer in the evening – known as a wet/dry cycle.
  • This is done so that air can enter back between the soil particles – roots need oxygen as well as moisture.
  • However, the soil should never dry out completely.
  • During this hot period, I’m watering my containers twice each day.


  • Bush varieties do not need pruning.
  • Remove side shoots from tall varieties.
  • Remove leaf branches up to the first truss on tall varieties.
  • Remove the growing tip after four or five trusses when growing outside.
  • Remove the stragglers – very small toms and flowers at the end of trusses – when the truss already has fully grown fruit.
The end of a truss. Removing the last few flowers.

Tomato Problems

The hot weather we’ve had in the UK means that there are fewer diseases around than usual. Many problems that effect tomatoes are caused by low temperatures and wet weather. Thankfully, it’s been a warm, dry summer so far!

Heat stress is probably the biggest issue at the moment.

Curled and cupped leaves that turn away from the sun, and fruit that has green shoulders (greenback) or patches where the lycopene (red pigment) hasn’t been able to develop because of the hot direct sunshine.

Keep roots cool

Tomato plants can also become stressed if the root area in a container becomes too hot. This happens especially when growing in dark coloured containers. Sticking a sheet of white plastic or paper to the front of dark or black pots helps!

Quadgrow Planter with white reflecting pots.

Greenhouse heat

If you grow tomatoes in a greenhouse, you and they will be feeling the heat. One newsletter reader suggested taking one or two glass panes out of the roof. A bit tricky but one way to get some fresh air in and heat out!

Flower set and humidity

In hot weather, when humidity is either very high or very low, flower set can be a problem too. Flowers fail to set as pollen is too dry to fertilize a flower’s ovary.

In dry air conditions – low humidity, pouring water on the greenhouse floor or around the base of a plant can help. When the air is high in moisture, tapping plant stems to help dislodge and move pollen around the flower can help too.

That’s it for another week … I believe we have more hot and humid weather on the horizon but It has rained overnight here in my part of the UK – we could do with it!


7 Responses

  1. Don Stedman
    | Reply

    Hi Nick.
    New one for me this year Heinze one they make the ketchup from.? not a bit like the picture on plant that I had, This showed round tomatoes mine are long shape fruit maybe labels got switched Fruit skin very tough not bad taste though. Will enquire when next in the nursery Big boys very tasty this year must for next year Regards Don

  2. Robert Smith
    | Reply

    Hi Nick
    Grateful as always for your very comprehensive advice, I am having a great success so far this season particularly with my Black Cherry plants in fact I could be doing with a two storey greenhouse (if there was such a thing) as even although I pinched out the growing tips the plants are bunching up at the peak of the greenhouse. Don’t know if the prolific growth and abundance of fruit is due solely to the weather or the fact that I started using an air pump with the quadgrows but whatever, I have been most impressed.
    Could I ask your advice again please, when should I stop feeding and when should I dispense with the air pump.
    Many thanks and Regards


    • Nick
      | Reply

      Hi Robert,

      Good to know you’ve had such success – I would say it is both the air pump and the weather!

      It’s best to feed until the last fruit matures because the potassium will bring the last tomatoes to maturity.

      The same applies to the air pump, but if you already have fantastic results, you could stop the extra aeration at the end of August.

      The extra air makes plants grow faster and the extra potassium feed bring fruit to maturity sooner.

  3. Andrew
    | Reply

    My Greenhouse plants are a mess this year blossom end rot on the San Marzano’s, under production on Sungold and Gardeners Delight. However the outdoor ones appear to be thiving, much easier to water and no heat stress.

    • Nick
      | Reply

      Hi Andrew,
      It’s difficult avoiding blossom end rot when growing toms with very fleshy fruit like San Marzano – especially when it’s hot.
      Probably, Sungold and Gardener’s Delight have struggled a bit with the greenhouse heat, as you say, outdoor toms are doing better.

  4. Jess Allaway
    | Reply

    Hi Nick,

    Quite a difficult year so far for me as a greenhouse only grower. Excessive low temperatures early on when plants were small followed by weeks of excessively high temperatures, although thank goodness they have dropped a bit now. The problem I am having right now is with all my Tumbler and Red Alert bush tomatoes. The Tumbler plants have become massive and the stems bending over as they are overloaded with large bunches of fruit and at the same time sending out huge amounts of flowers. I feel I should be in there removing flowers but hardly know where to start. The Red Alert plants are behaving like indeterminate and heading for the sky. Have Been enjoying lovely tomatoes these past three weeks, so shouldn’t be complaining but I feel the Tumblers are almost destroying themselves with over production. Never experienced this problem before. Guess it must be weather related. A great year for the outside growers I would think. Hope so.

    • Nick
      | Reply

      Hi Jess,
      Good to hear from you as always!
      You may have to remove some of the flowers – I remember having the same problem and it would have been impossible for the plant to produce fruit from every flower. Remove a few of the smaller flower/bud clusters – that should do it!

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