Most of my tall varieties have now reached the polytunnel roof, so it’s time to begin removing the growing tips.

The last couple of weeks I’ve mention about pruning and how it can be used to encourage plants from the vegetative to the reproductive phase where emphasis is on growing tomatoes rather than growing leaves.

Another way to encourage plants into the fruiting mode is by the amount of food we give them, also known as increasing the nutrient strength.

Steering by feeding
Plants that are given a weaker feed tend to be more vegetative than those given a stronger feed. In other words, feeding plants a slightly stronger strength of food will encourage the reproductive phase and fruiting. Feeding tomato plants a slightly weaker strength of food will tend to keep them in their vegetative mode and delay fruiting.

Now you may say … what was all that stuff about not feeding plants too much …. and, it’s better to feed little and often – wouldn’t that also keep them in their vegetative mode?

The answer is that the two tips above work well as a general rule, but as our plants approach the desired amount of trusses, it is all about encouraging them to put their energy into growing tomatoes. The method I’m about to describe is a temporary boost.

Sweetheart variety growing in 3 inch Grodan cube - you don't need lots of soil to grow tomatoes.
Sweetheart growing in 3 inch Grodan cube – you don’t need lots of soil to grow tomatoes.

How much extra should I give and for how long?
After your container grown plants have been in their present soil for about six weeks and the nutrients in their soil have been almost entirely used up, the plants will depend on us for almost all their nutrients. At this point the recommended dose for feeding plants growing in soil can be doubled!

I am talking about plants that have reached a good size and have the amount of flowering/fruiting trusses you are happy with – usually four to seven trusses for a tall variety.

The advantages of increasing the nutrient strength

  • Steers plants away from leaf growth
  • Increased fruit growth
  • Sweeter tasting fruit if done when the tomatoes are swelling

The disadvantages if too much food is given

  • Wilting in hot weather
  • Increased risk of blossom end rot
  • Slightly smaller size fruit

Most Tomorite type feeds are reduced to half strength to allow for the nutrients in the soil. However, when the nutrients in the soil have been more or less used up by a plant in a container or grow bag, the given food can be increased – by up to double the standard diluted rate.

For how long?
Every July I give my soil grown plants a three week boost of tomato food. This can be done in two ways…

  1. Feed the same amount twice as often
  2. Double the strength and feed at the same intervals

The first option is less stressful for your plants, especially in hot weather, because adding more mineral salts to their water supply reduces the speed at which they can absorb water (see osmosis).

Flushing the soil
After the boost period of three weeks, plants should be given a good flush with plain water to remove any build up of mineral salts, then resume standard feeding.

Warning – Disclaimer
Do this with care … it’s best to try it on just a few of your plants and compare the results to those fed with only a standard amount of feed. I think you will find that the tomatoes given the higher strength/frequency feed will taste better and the plants will be more productive. Remember to stop after around three weeks!

The King Flower
The first flower on each truss (the flower nearest the main stem) is sometimes known as the king flower.

It is usually the first one to set, and because of this, has the greatest demand on the plant. It’s a bit like a nest full of birds – the one that shouts the loudest gets the most food and is the biggest!

Demand and supply
Not all tomatoes on a truss are equal – the ones nearest the stem are usually the sweetest because they are nearest the food supply.
Because of the dominance of the king flower and its tomato, many growers remove the first flower on each truss before it sets. This has the advantage of allowing the rest of the tomatoes to grow to a more consistent size and shares the plants resources more evenly between the rest of the tomatoes.

I’m not suggesting we start removing the king flowers, but it is one reason why tomatoes on a truss can grow to inconsistent sizes.

The weeks are flying by!


17 Responses

  1. michael.lewis
    | Reply

    good morning nick,i cannot understand why the cause I have 8 tom plants in my ghouse and 10 in my polytunnel, I feed and water these plants exactly the same but 1 of the plants has started with ber,i would be glad of advice should I destroy the affected plant also would spraying all the plants with dithane 945 help the problem
    kind regards
    mike lewis

  2. stephen clark
    | Reply

    hi Nick,
    a question, at this time of year i have many tomatoes various sizes and even more yellow flowers yet to set, my question is when do you decide to remove the yellow flowers that have no chance of growing into full fruit, i.e. on shirley, alcante etc,
    cheers Nick

    • Nick
      | Reply

      Hi Steve,
      The end of July is the time at which I get serious with pruning stragglers on the end of trusses.
      However, if you are growing a medium or large variety and you already have 8 to 12 good size fruit and a few flowers on the end of a truss, I would remove the flowers now.
      Sometimes, it may be necessary to remove a whole truss if almost all the flowers have failed to set and there’s no chance of decent size fruit before the end of the season.

      • stephen clark
        | Reply

        thank you Nick for great advice as always

  3. Rhys Jaggar
    | Reply

    I think I can agree with you about food strength Nick as I have done the experiment you suggested, not for the reasons you suggested but because I thought only the beefsteaks would tolerate the higher doses at that stage.

    Both my Super Marmande and my dodgy origin absolutely humungous beefsteak variety have orange fruit appearing already (the ripening ones are very, very large by the standards of each plant), whereas the Shirleys, Alicante and Ailsa Craig have lots of tomatoes, but all are green and yet to reach full size (each have around 50 – 60 fruit of visible size). I used 1000ml of half-strength tomorite daily for about a week on the beefsteaks (using 500ml of half-strength on the others). I also used 1000ml on Black Cherry, but that was because the plant was so big and had so many trusses that I thought it was the minimum necessary to get the fruit to grow out!

    It sounds like it is time for me to double the dose on the salad tomato plants for three weeks and see where we are then.

    Thanks for the tips as always.

    • Nick
      | Reply

      Hi Rhys,
      I’m pleased that you have tried the higher doses and have found them to be successful. As you’ve found out by experience, responding to the needs of plants at their different stages of growth is the more flexible way to feed and usually produces better results.

  4. Buster
    | Reply

    Thanks for your site Nick. Lots of information & different experiences of growing the blighters.
    So far no problem with BER inside or out of greenhouse.
    First few trusses on Tamina & Amateur are so good I’m pinching out the leaders before the pot falls over!
    Red Alert first to ripen now a Tamina.


    • Nick
      | Reply

      Hi Buster,
      Glad to hear you are without BER!
      I’ve had a really heavy crop on my Tamina and Amateur too and they are just beginning to ripen at a good size.

  5. Douglas
    | Reply

    Hi Nick. …
    Im not trying to be clever but this last newsletter regarding doubling amount of tomato feed has left me somewhat puzzled. I always thought that over feeding was as bad ,if not worse than underfeeding.The pros and cons here as regards more likely to develop BER and wilting and smaller sized fruit with higher amounts of feed leaves me scratching my head to be honest….Overfeeding is supposed to affect the taste,cause splitting and odd shaped fruit so ive been led to believe seems you are damned if you do …and damned if you dont.On one side we are encouraged to feed with half as much feed ,but twice as it seems we are encouraged to feed at double the recommended amount. Both ends of the spectrum there…Im lost Im afraid.
    By the way Ive had 3 cherry tomaytoes (black opal…a relative of black cherry supposedly) affected with BER this early. I thought cherry toms werent generally affected with BER…….maybe its an ominous sign for me this season. regards

    • Nick
      | Reply

      Hi Douglas,
      I can understand your frustration – the problem is, there are many different ways to feed tomatoes so it’s best to find a way that suits you and stick to it!
      It’s rare for cherry tomatoes to be affected, so it goes to show how unusually hot this summer has been so far.
      It’s caused because plants can’t get enough water – an interruption in their water supply. Reservoirs and watering valves are the way to go, but even these aren’t full proof in this heat.

      • Lauren
        | Reply

        Hi Nick,

        Could you recommend an organic tomato feed?



        • Nick
          | Reply

          Hi Lauren,
          At this time of the season I would recommend Miracle Grow, Organic Choice liquid feed. Its NPK is 326 and has a good strength and low pH.

  6. Valerie
    | Reply

    Good morning Nick.
    Well,my toms are suffering from blossom end rot.After growing toms for nearly forty years this is only the second time it has happened.I thought I had the watering sorted by growing in dirt pods,on capillary matting.and then on trays.I have given them a spray of milk.How often is this needed and also increased my watering regime and feed as of today.My GH gets very hot,even with automatic windows,vents on three sides,
    A double door wide open and roof blinds.We had an ugly gumtree felled two years ago and It provided some shade.This fits in with the appearance of blossom end rot!! Apart from water is there anything I should be doing?
    It is very dissapoiting to have to throw away a future crop. .P.S. I do water my GH floor!

    • Nick
      | Reply

      Hi Valerie,
      It’s really too hot for growing tomatoes and the BER is caused by a plant needing more water than it can get so there is an interruption to its circulation and calcium becomes unavailable.
      I normally spray once or twice every two weeks depending on the size of fruit, but I don’t think that in this heat it will make much difference. Reservoirs, watering valves and plenty of shade (as you suggest) will help.

      • Valerie
        | Reply

        Hello Nick
        I have had another thought about BER.I was given my current greenhouse two years ago.I collect rainwater and have had sufficient for the toms.Upto then I used mains water.We live in a very hard water area and I wondered if this would have an effect on the getting extra calcium? I am determined to solve my BER problem!
        As regards heat one sees toms in Spain etc under the boiling sun so they must be able to stand quite a high temp.

        • Nick
          | Reply

          Hi Valerie,
          Blossom end rot is caused be a calcium deficiency so If you live in a hard water area, there will be calcium in the tap water already and that would help prevent BER.
          The problem is, because calcium cannot be moved around a plant (it’s immobile), if there is an interruption to water intake, calcium becomes unavailable to the fruit and the result is BER.
          The only way to avoid it is to have water available to plants 24/7 as in a reservoir or watering valve. It also helps to reduce the need for water by reducing transpiration by shading plants and reducing the amount of leaves by removing the lower leaf branches.
          So far this season I have had three tomatoes with BER – all large varieties and I have hundreds of toms growing.
          The tomatoes in Spain are varieties that can cope with high temperatures (perhaps we should be growing some of those!) and transpiration is reduced by plastic sheeting above which keeps the humidity higher than outside, and when the temperatures drop at night, condensation forms on the plastic and water droplets fall back down on the plants – most are owned by Dutch growers … they are very clever at growing things!

          • Valerie

            Thank you Nick.Very interesting .I am moving three of my plant to a small shady GH! Will let you know what happens.

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