It’s been a warm week for many of us in the UK and a quick look around the plants in my polytunnel shows that some tomato varieties cope better with the heat than others.

With the prospect of more warm weather to come, here are a few tips on how to avoid plants becoming stressed.

Shade cloth
One of the most useful items to have at hand is garden fleece. It’s very good at protecting plants from direct sunlight – especially young or newly potted plants that have smaller roots systems.

Water spray
Not only essential for foliar feeding but excellent for reviving plants that are wilting!

Leaf curl and cupping
Leaves curling and cupping is a sign of heat stress. You may sometimes see a plant twist an entire leaf branch away from direct sunlight. Learning to read what a plant needs by its behaviour, especially through the leaves, is one of the most important aspects of tomato growing. However, some varieties curl, cup or roll their leaves whatever the temperature – it’s a variety thing!

Leaf cupping on tomato plant
Leaf cupping on tomato plant.

 

White reflective surfaces
This is very useful for increasing light, but when it’s very hot, it also helps prevent plant roots in black pots from becoming over-heated. It can get very hot in a black pot that’s in direct sunlight.

Stand pots in trays
In normal circumstances, it’s not a good idea to stand large pots and containers in trays of water for more than a few hours as it keeps the potting compost saturated and we know that roots need oxygen as well as water. However, an inch or two of water in a large tray (after the pots have been watered) will keep plants going through the day. Best make sure the tray is dry before night time.

Don’t feed
Mineral salts (tomato food) reduce the amount of pure water that a plant can absorb.
In hot weather, plants require much more water than usual – even feeding a moderate amount will interfere with water uptake, so it’s best to delay feeding until temperatures fall. This does not apply to organic feeding, only those feeds that are similar to Tomorite or Miracle Grow that contain mineral salts.

Photosynthesis stops when temperatures are too high
On a more technical note, photosynthesis stops when temperatures rise above 35C. However, the rate of food used by respiration (see respiration) rises above the rate that food is made by photosynthesis.
Plant growth comes to a stop and tomatoes lose their sweetness.

In other words, when temperatures are too high for too long, plants run out of the food/sugars they make in their leaves and tomatoes taste watery.

Small containers
The most vulnerable container to drying out in hot weather is the patio hanging basket and of course the more plants in a basket, the more often it will need water.

If you have several hanging baskets, or any other type of container for that matter, a drip system on an automatic timer is probably the best way to water – you often see them outside pubs … not that I often visit pubs to see if they have a watering system!!!

That’s it for this week … how are your plants doing so far this season?

Regards (or should I say cheers!),

Nick

 

 

18 Responses

  1. John
    | Reply

    Is it good idea to reduce the amount of leaf on tomato plants in hot weather to lower transpiration?

  2. Norman Anderson
    | Reply

    I have had a rather disastrous year, all of my pots are black which I think attracted the heat as most of the plants seem stunted and the tomatoes are not ripening at the top, so next year I am going to cover the pots with white plastic and use fleecing to minimise the heat at the root level in the pots. Is there any further advice I can be given in relation to this problem

    • Nick
      | Reply

      Hi Norman,
      You are probably right about the black pots causing the problem, but water stress, too much and too little, may also have added to the problem. The colour of the leaves are also a good indicator when things go wrong and woody stunted plants indicate a possible calcium deficiency.
      Nick

  3. Malcolm
    | Reply

    Hi Nick,

    I am at the stage now of deciding when to pinch out the top of my tomato plants. I am growing three varieties of cherry tomatoes in an unheated greenhouse, using the quadgrow container system. I understand the principle that the more trusses allowed to develop on a plant, the longer it will take for the fruits to mature, but was wondering if it is true that the fewer trusses allowed to develop on a plant, the higher the number of fruits produced by each truss?

    Thanks for any advice.

    Malcolm

    • Nick
      | Reply

      Hi Malcolm,
      In an unheated greenhouse I would allow six or seven trusses on a single stem indeterminate cherry variety.
      The amount of flowers on each truss is determined by a number of factors including light, temperature, vigour and balance between vegetative and reproductive phase.
      However, a plant only has a limited amount of energy, so it is possible that given the right timing, more flowers and fruit would appear from trusses if the growing tip is removed early.
      By the time the growing tip is removed, most of the flowers on the lower trusses are already formed and any stragglers should be removed to promote growth on the higher trusses.
      Regards,
      Nick

  4. Jess Allaway
    | Reply

    Hi Nick,
    Everything jumping up here this last week or so. Am wondering what I am doing wrong. My indeterminates have still a bit of growing to do and are mainly all about four feet high but only have, as per usual (for me that is!) three/maximum four trusses each. Fourteen trusses would have them visiting the neighbours! Should I have been doing something to get more trusses relative to height? Air pots doing well and looking forward to seeing the end result for those.
    Thanks for another very interesting newsletter.
    Regards,
    Jess.

    • Nick
      | Reply

      Hi Jess,
      Your results are quite normal for this time of the season – my plants are about the same except for the ones I sowed very early and pampered through the dark days of late winter.
      Air pots look really good and perform well too – because of the cavity at the bottom of the pot, you can stand them in water and roots will grow down for a drink.
      Regards,
      Nick

  5. nik scott
    | Reply

    Nick,
    great info thanks. I especially liked the piece you did about CO2 production, and have made my own CO2 production units which are bubbling away.
    out of interest when is your earliest ripe tomato and what is the variety ?
    last year mine was Stupice, seed put in pot January 1 and ripe tomato june 28. I would also be interested to hear from others about their earliest ripe toms. I live in west Cumbria by the way.
    regards
    nik

    • buster
      | Reply

      Hi Nik. Best growers for myself at the moment in the West Midlands are ‘Tamina’, ‘The Amateur’, plus ‘Red Alert’. Lot’s of solid toms developing on all. No signs of any problems yet! At least 2 weeks away from a red ripe one though.

      buster

      • Nick
        | Reply

        Hi Buster,
        That’s funny … I have the same varieties doing very well too! I’ve double-stemmed the Bejbino and it’s taking over the polytunnel!
        Cheers,
        Nick

    • Nick
      | Reply

      Hi Nik,
      I usually have a ripe tomato or two from Red Alert around the middle of June but this year it will probably be the end of June. The fruit on my Red Alert plants have grown bigger than normal, probably because of the bright weather we’ve had, so are taking a bit longer to ripen.
      Most of my other plants will start to ripen from mid July.
      Regards,
      Nick

  6. Rhys Jaggar
    | Reply

    Thanks for the tip on beefsteaks Nick, I’ll definitely try that. The first truss has most certainly set well – the toms are about 2 – 3 inch diameter on Truss 1 (4 of them), so they’re well away.

  7. Valerie
    | Reply

    Good Morning Nick
    I am awed by Rhys’s comments! My toms are fine and have turned from spindlely little fellows into nice robust toms.I am nervous about putting them outside but will have to as they a bit crowded in the GH.As usual I grow too many but supply a granddaughter with a small back yard in London,a next door neighbour who I introduced to tomato growing and the remaining extra half dozen to my gardening helper who sells them for his “chicken fund”.I do get eggs in return!

    • Nick
      | Reply

      Hi Valerie,
      It’s nice to know they go to a good home – a fresh egg is almost as good as a freshly picked tomato!
      Regards,
      Nick

  8. Rhys Jaggar
    | Reply

    Similar story to you down here, Nick.

    The sunshine has seen the production of new trusses and the flowering of plants come on very rapidly – I can scarcely believe that my Alicante has now produced 14 trusses (all I need for the season), Black Cherry has produced 30, Ailsa Craig has produced 10 and Super Marmande 10. They are all so far ahead of last year that it’s astonishing. Having harvested nearly 20 Maskotka+Glaciers by the middle of June is something I’ve never managed before!!

    Heat sensitive plants include Ailsa Craig (I knew that from last year, but even 24C produces a bit of heat stress), Black Cherry, Riesentraube and Ferline. Apero, Sungold both curl the very top leaves into a tight ball but it hasn’t stopped them setting their first trusses well. Alicante likes the heat, Shirley is fine with it as are Maskotka and Glacier.

    The most efficient fruit setters right now appear to be Alicante, Ailsa Craig, Shirley, Super Marmande. The two big beefsteak varieties are being fussy this year. They set truss 1 properly or partly but are not setting properly further up the plant. Plant growth continues and I’ve been giving them potassium shots, so I’m somewhat stumped. I give them the same as Shirley, Alicante and Super Marmande all of which have been setting brilliantly.

    At least all my plants are now in their final homes, with the Red Alerts and Cedricos potted up last night.

    Good to see you continuing to anticipate all the issues my tomatoes face each week Nick!!

    Keep up the good work.

    • Nick
      | Reply

      Hi Rhys,
      Sounds very impressive as usual and your plants are certainly very well advanced.
      With beefsteak tomatoes, after the first truss has set, give them a burst of nitrogen for a couple of weeks to encourage further growth higher on the plant – this should also encourage the higher trusses to develop (as long as the first truss has set). As you know, many of the large varieties tend to run out of steam early.
      Regards,
      Nick

  9. John Bowtell
    | Reply

    Hi Nick,
    Tomatoes leaping up especially Cossack and my Lidl experiment Harzfeuer: very cheap seeds, all germinated all growing like the clappers. Will let you know if they turn out to be as good as they look now. Hopefully will have some good outdoor plants if the weather stays right.
    Regards,
    John

    • Nick
      | Reply

      Hi John,
      So far so good … fingers crossed and it could be an excellent season both inside and outside in the garden.
      I tried Harzfeuer from Lidl last season and they are a very good medium size tom.
      Regards,
      Nick

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