Tomato Seedlings and High Temperatures

This week: Tomato seedlings and high temperatures, beware of the pigeons, take the quiz, reasons why we don’t sow tomato seed directly in garden soil.

Can seedlings have too much sun?

It’s been a fabulous week for sunshine here in the UK.

I don’t want to grumble but it’s been too hot under cover – conservatory, greenhouse etc., and at times, it’s been too breezy on the patio for small seedlings. What a hard man to please!!!


Beware of pigeons!

A few seasons ago, I put a tray of seedlings out on the patio and a pigeon pecked the top off of each one!


We know that tomato plants like full sun but there is a danger of too much sun for seedlings.

Tomato Seedlings and High Temperatures
Seedlings in Rootit Sponges


Garden fleece is a good way to reduce direct sunlight. If kept in the strong sun for too long, you may find that leaves begin to twist or cup as they try to turn away from the sun.

It’s sometimes difficult to know what the weather is going to be like in your garden, if you are out at work all day – but best to be safe than sorry with seedlings. Better in the shade than damaged in full sun.

Wilting seedlings can be given a misting with water (when in the shade) to rehydrate. Spraying water onto plants in direct sunlight can damage leaves.


The Quiz

I thought it may be fun to have a quiz this week. So that everybody can take part, the answers are in the text below, so read that first if you wish. Click the link at the end to take the quiz.

[Note: Requires Adobe Flash – works best on PC’s. For Android install the Puffin Browser via Google Play.]


Tomatoes originate from South America but Italy is often thought to be the home of the tomato because it is so widely grown there and used in Italian cooking.

There are two types of tomato plant:

  • Tall – often called indeterminate or cordon.
  • Bush – often called determinate.

Bush varieties may be divided into three types:

  • Trailing – great for hanging baskets and high sided containers.
  • Dwarf upright – ideal for growing on the kitchen windowsill.
  • Larger upright – such as Maskotka and Red Alert. These are larger plants with some trailing habit but prefer to grow in larger pots.

Salad tomatoes are medium size – one of the old-timers that has been very popular over the years is Moneymaker. My first two tomato plants were Moneymaker and Alicante – both salad varieties.

The tomato is a fruit because it contains seeds.

In America it was classified as a vegetable in order to avoid import tax.

If you grow indeterminate (cordon) tomatoes in a greenhouse, you can allow the plants to grow up to the greenhouse roof. This will produce between six and ten trusses – depending on the height of your greenhouse.

If you grow outside in a short season area like the UK, it’s best to allow four or five trusses on your cordon varieties.

  • Nitrogen for top growth.
  • Phosphorus for root growth.
  • Potassium for flower and fruiting.

Over feeding can cause a build up of chemicals in the soil that is harmful to roots.

There are a number of reasons why we don’t sow tomato seeds directly in garden soil:..

  • The seeds will be slow to germinate at lower temperatures.
  • Seedlings will be attacked by insects and diseases.
  • Sowing in small pots or seed trays of fresh potting compost will produce the best results.

Bush tomato plants are best grown in high sided containers to keep the fruit up, off the ground and away from slugs and snails etc.

A well grown cherry bush variety can produce well over 100 tomatoes!

Take the Quiz here

There is no prize but If you score 8/10 or higher, you may award yourself the honorary title: “Master of Tomatoes”.

Have a sunny weekend!



13 Responses

  1. Robert Smith
    | Reply

    Hi Nick
    Not wanting to use my fan heater in the greenhouse I am putting the tomato plants out in the forenoon and bringing them back indoors in the early evening, four of the plants, ie black cherries are getting fairly tall at almost 12 inches from the seed leaves to the top of the stem, when I eventually manage to plant them in the quadgrow pots how deep into the pots can they go to avoid the first trusses being too high and therefor perhaps getting fewer trusses before the plants reach the greenhouse roof !
    Best Regards

    • Nick
      | Reply

      Hi Rob,
      You can plant them as deep as you like – remove the seed leaves, you can also remove the lowest leaf branch if necessary.
      It takes around two weeks for the roots to begin to grow out of the main stem that’s below the soil surface but you should see the benefit after about a month.

  2. David
    | Reply

    I took the quiz & got 80%! 🙂 One I got wrong because I didn’t read it correctly, in fact it was the one question that made me laugh! The other I honestly didn’t know. 🙁 I won’t say which ones I got wrong so as not to spoil the fun for others.

    So, Can I consider myself a Master Tomato Grower? 😀

    Thanks for that, Nick! 🙂

    • Nick
      | Reply

      Hi David (MT),

      You may now consider yourself a Master Tomato Grower! 🙂

  3. David
    | Reply

    Hi Nick & thanks again for producing the newsletter. I think it’s an interesting idea to do a quiz, spices up the newsletter even more & who doesn’t like a challenge once in awhile?

    Unfortunately the very hot sunshine shriveled up my ‘Tumbling Tom Red’ seedlings on the balcony! 🙁 I had left them in the propagator on the table on our balcony but forgot to move them off to a shadier spot before my wife & I went out to visit our daughter & grandkids in a village 5 miles away. When I checked on them the next day I saw they were dead – cooked in the hot sunshine & trapped inside the propagator with the vents closed!

    Do you think it’s now too late to try again?

    All my other seedlings have their first pair of true leaves now & are looking very healthy! I sowed 5 varieties & have loads of seedlings!

    • Nick
      | Reply

      Hi David,

      You can still sow quick growing cherry varieties – if you really want Tumbling Tom, I expect that they sell them as small plants at your local garden center.


  4. Rachel
    | Reply

    Loved the quiz thanks Nick. I always learn so much from your newsletters 🙂 My tomatoes (piccolo, yellow tumbling toms, sweet million – can you tell I like the small ones?!!) are coming on really well and I plan to plant them out in the greenhouse this week. Rachel

    • Nick
      | Reply

      Hi Rachel,
      That’s a great selection of cherry toms!
      The small ones are the usually the best tasting, unless you live in the south of France or Italy where there is a lot of sun and large tomatoes can develop their full flavour.

  5. Rob
    | Reply

    Hi Nick,

    April temps not *too* normal, please! I’ve just put my first batch of indoor toms into the greenhouse. Knowing my luck, I’ve also got the greenhouse heater on standby.

    Just for fun, I sowed a couple of Sub Arctic Plenty on New Year’s Day and nursed them in a south-facing bay window. These went into the greenhouse last week looking healthy and in flower. I also sowed a couple of Maskotka and while they haven’t come on as quickly, they do look as though they will flower in a couple of weeks. These plants should have a nice head start when the time comes to put them outdoors.

    Thank you for another fascinating newsletter.

    • Nick
      | Reply

      Hi Rob,

      I used to grow Sub Arctic Plenty along with Siberian – both very early and good results.
      I’m pleased you enjoy the newsletters!


  6. Rhys Jaggar
    | Reply

    We have had temperatures more akin to Italy in high summer the past two days: closer to 30C than 25C in mid to late afternoon. So my earliest tomatoes lived in the more shady areas while the younger ones sat near open windows to get a bit of cooling breeze.

    It has to be said, the first three weeks of April have been perfect for my equinox sown seedlings: not too hot and sunny to begin with, warm sunshine in the third week as the plants are growing away well.

    My Red Alerts for the soil came through in 4 or 5 days this past week, just the competition seeds next week and we are fully sown.

    Forecast suggests a return to normal April temps this week, so all good for tomatoes, potatoes and onions.

    • Nick
      | Reply

      It’s great to have this boost of sun for the more mature tomato plants but I think it is easier to cope when the weather is a little more moderate. Looking forward to normal April temps!

      • Rhys Jaggar
        | Reply

        I must say I used the hot weather to germinate squash and cucumber seeds very well last week. I had just built a complete compost heap after cutting the grass for the first time and the heat of the heap allied to hot sunny weather brought through all the seedlings in five days.

        For every bane there sems to be an opportunity too!

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