Do they need a bigger pot?

[womble]

I thought that grow bags had a better make up of material than std MP compost?
It's great that you can make up bags and pots easily at home, you've probably got piles of well rotted manure around, decent soil to use and MP compost by the bale, you also have intimate knowledge of how to do it and immense self belief because of years of practice.
But if you're just starting out with nothing apart from a pot full of tomato plants, but no other equipment, having a couple of these bags to start with, isn't bad and then next year they can build on that experience.

[Nicos]

To be honest- I think it comes down to initial start up cost( and how much £ you can spare)- and how much space you have.
I've found that growbags have always needed a bit more watering than tubs- and being a teeny bit lazy I prefer not to make extra work for myself.

This is a fantastic example ANewGrower how different gardeners will give you different answers....all based on their experiences.
We're all on a learning curve here- and sometimes it's good to try out other peeps methods to compare to your own!

Sound advice from everyone- now you need to tweek it to fit in with your lifestyle!

[Two_Sheds]

I thought that grow bags had a better make up of material than std MP compost?

I don't believe so. If anything, the cheap growbags are little more than dust and floor sweepings, with a bit of feed mixed in if you're lucky.
As most people, if not everyone, feeds their tomatoes anyway, there's little point in paying extra for compost with feed added.

[womble]

These aren't the cheap ones and they are well filled from what I saw.

In fact if you were to ask me the best medium to grow tomatoes in, I would say from the top.

1. Ground, with manure and leaf mould if you have it.
2. Ground, just decent soil.
3. Pots, as 1.
4. Pots filled with, or good growbags cut in half and on their ends.
5. Pots, a mixture of MP compost and manure/soil.
6. Pots, just MP compost

[Florence Fennel]

You're doing really well already, just follow the advice you've been given on here and pot them individually. Let us know how you progress!