Tomato plant roots have a great sense of touch and it is this sense of touch that tells them to “get on with it!”

When their roots reach the sides of a small pot, it triggers the plant into quicker growth and earlier maturity. This is because the plant knows it has a limited area in which to grow, and therefore, a limited time in which to produce tomatoes and seeds for further generations of its kind.

Tomato Root StructureA healthy root system and time to pot on.

This is one of the reasons we start with small pots and then pot on into bigger pots. To encourage plants to maturity sooner rather than later.

It also saves space – if you had a hundred seedlings, each in a 10 inch pot, you’d need a lot of room!

The later in the season that you start, the less pot sizes you’ll need. This is because the period between seedling and final position is shorter owing to plants growing more quickly due to better weather – hopefully!

Here’s a photo of my pot sizes – I started in January. If you started in March or the beginning of April, you can omit a pot size.

Tomato Pot SizesThe plant in the large pot is a Red Alert (bush variety)

After the seeds had germinated, I began with a 3 inch pot, then 4 inch, then 5 inch and the final large pot is about 16 inches at the top – any large pot 9 inches or bigger is fine.

It’s best if the plant in the 5 inch pot is in flower before planting in the largest final position pot. This will prevent it from becoming too leafy.

I bought the large pot for £1.00 in Poundland – it’s perfect for a Red Alert bush or trailing variety like Tumbling Tom. Tall pots will keep the tomatoes off the ground as they cascade over the sides.

Tall varieties are best grown in grow bags or tomato pots that aren’t so high off the ground. It makes it easier to pick the higher trusses.

Why not keep a plant in a 3 inch pot until its final position (big pot)?

When plants become root-bound (kept in a small pot for too long) they run out of steam and become unhealthy.

Some growers use this technique to force plants on to maturity sooner – it’s called “forcing”. However, you need to know exactly when to pot on otherwise it will have the negative affects already mentioned.

5 Responses

  1. Wilson Baskett
    | Reply

    Dear Nick.
    My three different types of tomato’s I have grown from seed are all doing better than I thought, and have more than I thought I was going to get.

    The variety’s I have are Beefsteaks, Gardeners delight and Sweet olive tomato’s. As I already said before I made two raised beds in the most sunny part of my garden.

    I was just wondering which ones would fair better in these, and which ones would do good in pots as I do not have much room left. Also what size pots would they require??

    • Nick
      | Reply

      Hi Wilson,
      I would grow the beefsteaks in the raised beds, where there is plenty of room for their roots.
      The smaller tomato varieties will be happy in either raised bed or pots. I like to grow them in the biggest pot I can find – anything from 10 inches or bigger for each plant.
      Pot grown plants need to be fed well – almost like hydroponic plants – to get the best results.

    • Andy
      | Reply

      Totally agree about the cherry or selmlar tomatoes. My annalise and yellow pear tomatoes are producing a ton of fruit, while the larger tomatoes require so much more work for such a small amount of fruit. I think I just might stick with salad tomatoes next year. Thanks for the tips on the suckers. I’m going to try not to by seed for the hybrids next year and over winter using this propagation method instead.

  2. Rhys Jaggar
    | Reply


    That’s a very clear system you use, but is there any evidence that slight variations makes any adverse differences?

    I have gone from seedling to a variety of pot sizes based on what we had – four in 3 inch pots, plenty in 5 inch pots and a few in six inch pots. They are all doing great and some are getting ready to be potted up into even bigger things soon.

    Also, any tips on how many days without water you should leave plants before potting up – getting the soil out in a oner seems harder if they are still a bit damp?

    • Nick
      | Reply

      Hi Rhys,
      I don’t think that slight variations will make a lot of difference. I keep my eye on the lowest proper leaves and if they begin to discolour a lot, I know it’s time the plant was in a bigger pot as it is running out of nutrients. Also, I may give it a feed before or just after potting on.

      I prefer to water plants after they’ve been potted on rather than before – as you say, it can be difficult getting the soil to keep its shape if it is too wet. Sometimes though, on a warm day, you don’t get a choice – the water comes first!

      I go by the weight of a pot – whether it is light and dry or heavy and wet – after a while you can tell how much moisture there is in the pot’s soil just by lifting it.

Leave a Reply

Your email address will not be published. Required fields are marked *