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Tomatoe planting

I'm always watching monty don use seed trays to start tomatoes.  He then painstakingly prickes them out into a larger container and then another larger container again.  Why not just plant them in the final container at the beggining?


  • Because you don't want to drown a tiny seed in a large container of damp compost. Germinate first and then progress. Just imagine yourself growing up in an a claggy, cold environment - same thing for plants.
    I'm not particularly a fan of MD but I think this is common knowledge for seed sowing.
  • Thank you
  • FairygirlFairygirl Posts: 54,350
    Yes - as @philippasmith2 says, it's not ideal for seeds to have huge amounts of wet compost round them as they germinate and grow initially. 
    It's the reason why seed trays are used, or anything else shallow that can be utilised. The shallow plastic trays that meat often comes in is also ideal. 
    Having said that, I usually sow my toms in 3 inch pots - usually 3 seeds in each, and they're sown round the edges of the pot. That also aids drainage. Mine are started indoors [as most people in the UK will do] and once they're big enough to handle, they're transplanted into a three inch pot of their own. It's easier to keep them drier and warmer in the house too. 
    They're transplanted again, and often once again into their final pots before they go in the greenhouse [we can't grow outside here] In warmer areas, where they're able to be grown outdoors, it's about timing, because of weather conditions. 

    All of that process means they're not sitting in cold, wet soil for long periods. It's the same for lots of seeds   :)
    It's a place where beautiful isn't enough of a word....

    I live in west central Scotland - not where that photo is...
  • Ante1Ante1 Posts: 2,961
    Every time when you transplant seedling, plant them deeper and they will grow roots from covered stem. They will have good developed roots when time come to plant them out or in the greenhouse.
  • thrxvsthrxvs Posts: 32
    Apologies but this is one of these urban myths around growing seedlings, in fact there is no scientific evidence at all that seedling will benefit from being potted on to gradually increasing pot size, IF everything else is completely equal. It has been stated that overpotting causes damage however there is no scientific evidence to support this claim. The argument around roots having too much wet around them also has no scientific basis. The root size of a plant of a particular size does not differ if it is in a small pot (unless it is pot bound and then you have other problems to worry about) or if it is in a large pot. The roots take up the same area and therefore they have the same surface exposure to the soil and therefore the moisture in the soil, it does not matter if the plant is in a small pot or in a large pot, either will drain to a certain point at which point it will stop draining and the water content per m3 will be the same. A larger pot will dry out more slowly than a smaller pot however this is irrelevant if you maintain a responsible watering reigime - your soil should never be wet but only damp so if your big pot is full of wet soil then the problem is with the watering method not the pot size. Similarly if your plant is in a small pot and the soil is dry then there is an issue around watering timings based on the environment the plant is in.

    Providing the pot has proper drainage the soil will drain equally regardless of whether the pot is a large pot or a small pot. If the pot is a large pot then there will be a larger volume of wet compost BUT the surface area of the roots touching the wet compost in the bigger pot will be the same as the surface area of the roots touching the compost in the smaller pot. Everything else being completely equal there is no scientific evidence whatsoever that potting onto a bigger pot is better than potting onto a smaller pot.


    If you are growing tomatoes specifically, then think about what you will achieve if you transplant into a larger pot vs transplanting into a smaller pot. Root size is related to foliage size. So what does that mean for a tomato plant? What is your eventual intention with the plant, do you want to keep it in a pot or are you going to plant it out into the greenhouse or outside. If the tomato plant is kept in a smaller pot then if the growing conditions are right then a smaller pot will restrict the growth (of the tomato plant) - this can be good if you are waiting for the right conditions for planting out, eg if it is still too cold. Conversely if you want to get the plant growing quickly because you need to plant out soon and need it a certain size to do that then putting it into a bigger pot will encourage it to grow faster and be ready quicker to plant out, but then you could argue that if conditions outside are ready then you could just plant straight out into it's final place without going through the rigmarole of potting onto a larger pot first. So it depends on what you need to do in a particular situation.

    Why does gardening recommend a small pot and science a big pot? Probably inexperienced gardeners tend to overwater and small pots hold less water and therefore less likely to be (apparently) overwatered. So therefore the easy advice to give is to water the small pot and have a small plant.

    So the short answer to the question that is asked is - it is not quite as clear cut as a blanket statement "overpotting = bad" and it depends on the plant and what you are doing with it in the longer term... for tomatoes it can be one tool of several to control plant size.

    But don't take my word for it, you are free to do your own research online and also try for yourself potting on vs just moving onto a much bigger pot. Personally I have tested the theory and have found no benefit from potting on tomato plants gradually.

  • UffUff Posts: 3,199
    There's some food for thought thrxvs. I'm open to any ideas and willing to adapt to them if there is firm evidence that they work. In this case, the one of potting on, there are a number of factors to consider I imagine so it isn't just a simple case of potting on to a size larger pot. Can you provide us with a link to the research you mention please as I would like to read about it and if proven it might save gardeners some time and effort in their work. 
    SW SCOTLAND but born in Derbyshire
  • Every year I grow about 20 tomato plants. I start them off in little trays in a windowsill propagator and prick them out into little pots, then they live on the dining room windowsill until the weather conditions are ok for them to go into my little lean to greenhouse before eventually being planted out into the veg patch or large pots. 
    If I started them off in large pots the windowsill wouldn’t be big enough 🤪 

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.

  • BenCottoBenCotto Posts: 4,573
    A great post @thrxvs. I love reading a well evidenced refutations of accepted practice. But @Dovefromabove has the perfect response - when seed sowing and potting on is in full swing, space in the greenhouse or the windowsill is at such a premium small pots make perfect sense.
    Rutland, England
  • DovefromaboveDovefromabove Posts: 86,876
    edited December 2021
    @BenCotto 😊 

    Another point I would make is that if, as the vast majority of gardeners do, we are using proprietary multi purpose compost it is likely to come with a fertiliser incorporated in the mix. This lasts quite a short period of time and if not absorbed by the plant will leach out. 

    If potting on at regular intervals into fresh compost this is obviously not a problem as this will contain more nutrients, and it’s only when the tomato plants have been in their final pots for a while and have set their first truss that the gardener has to purchase a potassium rich  fertiliser to feed the fruiting tomatoes. 

    However, if the seedlings start and continue life in their final pots the nutrition in the compost will soon be exhausted/leached out and the gardener will be having to purchase and apply an additional general feed to the pots for the growing period … if the pots are larger than the rootball then much of the feed will again be leaching out and going to waste.  

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.

  • FireFire Posts: 18,026
    thrxvs said:
    Apologies but this is one of these urban myths around growing seedlings, in fact there is no scientific evidence at all that seedling will benefit from being potted on to gradually increasing pot size.

    There has been discussion of the real virtues of potting on across the forum over the years. I'm interested in the evidenced practice too. I don't really get the science behind the idea of having to pot on.

    As with many of these questions, I think it would be very easy to set up some tests over the summer to see what happens, setting up various planting conditions in as similar settings (earth, water, seeds etc) as possible.

    It would be interesting to bring curiosity and investigation to the question.... 

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