Best Container Sizes for Tomatoes
One question I’m regularly asked is “are some container sizes for tomatoes better than others?” for planting tomatoes in their final position that is.

The answer depends on a number of things including plant size, fruit size, leaf size, early or late to mature etc.

Various pots and container sizes for tomatoes

For example, a dwarf variety can grow in a 6 inch pot but most beefsteak varieties will need a much larger area for their roots.

See also: Best container size for tomatoes

Various container sizes for tomatoes

A variety with a large leaf area will require a bigger pot (in theory) because it will lose more moisture through its leaves and therefore require a larger soil area from which to draw water.

Also, a variety that matures early may need less growing room because its season is shorter than a late maturing variety for example, so it needs less resources.

As valid, and long winded, as these points may be, they don’t get to the heart of the matter.

Better growing methods mean you can use smaller pots

The fact is, the better the growing methods used (i.e. growing media, type of container and access to water and nutrients), the smaller the container size that is required for a successful crop.

The plant below is Sweet Aperitif growing in an 8.5 litre pot using the Auto Pot system. It was trained to three stems.

Tomato Sweet Aperitif growing in an 8.5 litre pot.
Sweet Aperitif on three stems growing in an autopot system.

For example, a tomato grower who uses the least expensive compost, a basic pot, waters and feeds inconsistently will need a bigger pot to achieve good results than someone who understands what their plants need and delivers it to them. The extra soil in a larger pot acts as a buffer zone or safety net!

With best growing practices, it’s possible to use a 10 litre rather than a 15 litre pot. It’s possible to grow most varieties successfully in a 6 litre pot too. It’s how we grow them that determines the pot size.

Container sizes vs garden border soil

The above applies to container growing. If planting directly into the garden soil, the bigger the root system, the better.

If growing in containers, there is a limit to the size the roots can grow before they become pot-bound.

The idea in container growing is to give a plant all it needs so its roots won’t become too large and pot bound.

It is the case that a plant that receives water and food 24/7 – that’s whenever it needs them, will grow a smaller root system and be happier in a smaller pot.

Disadvantages of large pots

Bigger pots are more expensive to buy, take up more room and need more potting compost. Two important considerations for most of us are expense and space, not to mention carrying the heavy bags of potting compost!

Of course the question now is: “what do tomato plants need?”

Creating the best growing conditions

They need a good medium that contains lots of oxygen and doesn’t dry out too quickly allowing good respiration (see below) and avoiding water stress (see hormones below).

They need access to water and nutrients 24/7 – when they want them, rather than when we give them – leading to consistent transpiration and osmosis (coming soon).

They need good aeration when in a greenhouse, tunnel or on the windowsill producing good transpiration and avoiding disease.

They need plenty of light to maximize photosynthesis.

Lots more on these subjects in coming newsletters.

Here’s a link to a very useful page if you are interested in some of the more technical aspects that make plants grow, click here.

Blowing in the wind

Every morning I blow gently on my seedlings!

This may seem a strange thing to do, but there are at least four good reasons why it helps growth.

  • Increases air flow in the window and helps get rid of any morning condensation.
  • The aeration increases transpiration (moisture loss from leaves) and gets the circulation going.
  • It provides extra carbon dioxide for photosynthesis – we exhale carbon dioxide.
  • The movement encourages stronger stems.

It’s long been suggested that talking or singing to plants encourages growth – the truth is, that plants grow better when subject to carbon dioxide. We inhale oxygen (for respiration) and breath out carbon dioxide – good for us and plants!

Respiration and Tomato Plants

It is useful to understand respiration because by creating the right conditions, plants grow faster, produce more tomatoes and are healthier.

So what is respiration?

It is a process that happens when plants combine the sugars they make during photosynthesis, with the oxygen they mainly absorb through their roots.

In other words, respiration is the process of combining sugars and oxygen to create energy for growth.

So what can we do to optimize respiration in our tomato plants – or least make sure we don’t hinder it!

The most important thing is to provide plenty of oxygen for plant roots. This can be achieved by using perlite, vermiculite, air and fabric pots etc.

Respiration plays an important role in organics too. A well aerated rich soil will encourage friendly bacteria, and they need oxygen to play their role just as much as the tomato plants do!

There’s always a trade-off between moisture and air in the root zone. Too much of one leads to a reduction of the other – the challenge is to maintain a regular supply of both.

More about container growing here

14 Responses

  1. Rhys Jaggar
    | Reply


    My 8cm pot seedlings this year are growing much faster than last. Maybe it’s due to the milder temps stopping my window sills getting cold, but first true leaves formed in under 2 weeks from sowing, nearly a week faster than last year. 2 days shy of three weeks the first side shoots have multiple leaves on and the Maskotkas are going vertical like Usain Bolt!

    My potting on mix in 8cm pots is:

    3 parts John Innes Number 1
    1 part MiracleGro
    1 part rotted horse manure
    5 parts perlite
    A handful of Pinetum Products’ Basaltic Rock Dust per full washing up tub of the above.

    I hand mixed it all to ensure that any lumps were well broken up but I’m too lazy to sieve it all!

    No science, but it seems to be doing well for Maskotka, Black Cherry, Sub-Arctic Plenty and Glacier.

    I sowed two strains of sweet peppers using my old tomato method and they took considerably longer to germinate and are barely forming true leaves after being planted on the same date as the tomatoes. I think I’ll give them perlite plus extras at the next potting up! It may also be that my commercial seeds are older than the tomato seeds I made last autumn.

    • Nick
      | Reply

      Hi Rhys,
      Looks like you’ve been planning well in advance and have an excellent potting mix there!
      The varieties you mention are a good reliable selection too – the weather is so unpredictable it’s worth having the ones most likely to succeed at the top of the list!

  2. Bernie Adey
    | Reply

    Hi Nick,
    I have been growing and using comfrey as a liquid fertilizer for about five years you can get it from the wild for nothing but it will spread everywhere out of control. I have never noticed comfrey seed on sale. Mine came from Henry Doubleday a special variety called Bocking 14 it is infertile so will not spread they supply it as root cuttings.

    I started with six cuttings and within two years I had six bushes that grew to a meter high giving me far more than I needed. When I attempted to thin it out to three bushes I found it kept coming back as it is almost impossible to get all the root out I had to carefully treat the small new plants as they appeared with systemic weed killer to stop them. I even had a couple of new plants appear between the original site and the route to my car where I guess I must have dropped an odd piece of root of the plants I was disposing of.

    It is a great plant stimulant almost anything that starts looking sad picks up after a couple of treatments with this, you can tell how good it is because of the stink your neighbours will love you when ever you give it a stir.

    A side benefit is it flowers for many months and all the time it is in bloom it will be smothered in bees. This year I am going to put a couple of vases of the blooms in the polytunnel when the tomatoes are flowering instead of the vibrater I used last year.

    Regards Bernie

    • Nick
      | Reply

      Hi Bernie,
      Thanks for the information – you are obviously someone who knows their comfrey!
      I’ve seen the Bocking 14 advertised so I might take the quicker root and buy a few cuttings as you suggest.

      • Rhys Jaggar
        | Reply


        I bought Bocking 14 last summer and am hoping for bumper harvests this summer. It grew like the wind between July when I transplanted from pots into the ground, until October. It’s already coming out in February and you can feed it fresh horse manure and it will eat it up gratefully.

        It’s reckoned to be the best strain based on the research of Hills at the Henry Doubleday RA back in the day.

  3. sonny
    | Reply

    hi Nick
    thanks for clearing that up for me, as it will be growbags and pots i will be planting in this year, i got hoselock trays and auto water drip feeding system i will be setting up soon. thanks again. sonny

  4. jess allaway
    | Reply

    Hi Nick, looking forward to a new season. I too always blow across my seedlings and, just to be on the safe side, I add a wee “aye, you’re all doing just fine!” Regards Jess.

    • Nick
      | Reply

      Hi Jess,
      I’m glad it’s not just me who blows on his seedlings … the words of encouragement are a good idea too!

  5. sonny
    | Reply

    sorry im new to all this its my first year.
    i read on this that a good root in plants are better and produce more, and how to get good roots in Tomatoes, but now you saying smaller root system needs less. how do i work out best for plants i got in? ….. sry as i said this my first year and trying to read as much as i can on it ,,,, many thanks.

    • Nick
      | Reply

      Hi Sonny,
      You raise a good point.
      If growing directly in the garden soil, the bigger the root system, the better.
      If growing in containers, there is a limit to the size the roots can grow before they become pot-bound.
      The idea in container growing is to give a plant all it needs so its roots won’t become too large and pot bound.
      It is the case that a plant that receives water and food 24/7 – that’s whenever it needs them, will grow a smaller root system and be happier in a smaller pot.

  6. mick w
    | Reply

    Hi nick
    Do you think drilling holes in the sides of ten litre pots would increase respiration ? Good newsletter.
    mick w.

    • Nick
      | Reply

      Hi Mick,
      Absolutely … it’s a good way to optimise a standard pot.

  7. Mick Loughrey
    | Reply

    Just to verify what you were saying about container size for tomato plants. I think it was the year 2000 that I grew brandywine beefsteak toms in 7 inch pots with pot saucers under each one. Every morning before I went to work I filled the saucers with diluted tomato feed. Did the same again when I got home in the evening. Had a fantastic crop of big juicy tomatoes.I think the good weather played a big part in the success of this. I also pinched out toms when they were pea sized and just left 5 to a truss.

    • Nick
      | Reply

      Hi Mick,
      You are obviously an experienced grower – when plants are given everything they need, they grow smaller root systems and therefore need less room.

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