What size container do I need?

Multi coloured containers can brighten any growing space.
If you’re about to get some containers to grow food in, you may be asking: ‘what size do I need?’ Here’s the information to help you decide.

Is depth or volume more important?

The general rule is: the bigger the pot, the bigger the crop.

The volume of the pot is more critical than the depth.

15cm (6 inches) is deep enough for most crops (although some root crops may need more), as long as the volume is large enough.

Pros and cons of big pots

There are several reasons why it is easier to grow successfully in larger pots:

  • They dry out less quickly. This makes watering easier. It also reduces the stress on your plants. Most crops don’t like rapidly fluctuating water levels – it slows their growth and often triggers premature bolting (this is when a plant goes to seed before you want it to – rocket and coriander do this a lot, for example).
  • They hold more nutrients, ideal for hungry vegetable crops.
  • They offer more space for the plants root systems – enabling the plant to grow bigger and stronger.
  • They’re better at sustaining beneficial soil life, like worms. This helps you to mimic natural soil growing conditions in your pots. This in turn makes for healthier and more disease resistant crops.

However, large post also have drawbacks

  • Critically, they take up precious space – space that many homes don’t have.
  • They weigh more, requiring more physical work to fill and move. Weight is also an important issue to consider if you’re growing on a balcony or rooftop.
  • They cost more (in both pot and soil)

Pros and cons of small pots

Smaller pots, on the other hand, are not as easy to grow in but are a good choice for some situations because:

  • They’re cheaper to buy and fill
  • They’re lighter and easier to move around,
  • They take up less space.
You can fit more small pots in a space - and they are easier to lift on to a shelf like this. Most leafy veg will grow fine in them.
You can fit more small pots in a space – and they are easier to lift on to a shelf like this. Most leafy veg will grow fine in them.

The downsides of small pots are

  • They dry out faster. This puts stress on the plant and creates more work for you watering. You can get round this problem by using a container with a water reservoir or setting up a self watering system.
  • They need more regular feeding – observe plants carefully.
  • You’re more limited in what will grow in them. Don’t try big hungry crops in them like courgettes.

What volume of pot do different crops need?

Nearly all edible plants grow better and bigger in larger pots. However some types of crops can be grown more successfully in smaller pots than others. Here are some general rules:

Fruiting crops

Most fruiting crops really do need a larger pot to fruit well. The larger the fruit they produce, the larger the pot they need. For example, squash do best in a container of 50 litres (10 gallons), while small chillies can be grown successfully in a 5 or 10 litre (1 to 2 gallon) pot, tomatoes in 10 to 20 litres (2 – 4 gallons).

Large fruiting crops like this squash need a big pot to grow well. This one is in a 50 litre (10 gallon) pot.
Large fruiting crops like this squash need a big pot to grow well. This one is in a 50 litre (10 gallon) pot.

Leafy crops

Leafy crops can be grown successfully in large or small pots. The difference is that in large pots, they will grow larger and can usually be harvested over a longer period. In small pots, the leaves will be smaller. However, as long as the plant is kept well watered the small leaves will taste just as good.

Root crops

Root crops are similar to leafy crops. You’ll get bigger roots in large pots than small pots.

Root crops like beetroot, carrots and potatoes, will grow ok in a 10 litre (2 gallon) bucket like this.
Root crops like beetroot, carrots and potatoes, will grow ok in a 10 litre (2 gallon) bucket like this.

So which is best?

If space, budget and weight is no issue, then large pots (20 litres / 5 gallon or larger) are usually the best choice for most crops.

But as urban growing IS usually constricted by space, weight or budget (and often  all three) a mix of sizes is often a good solution. The best solution for you will depend on how much space you have and what you want to grow.

This is what I usually do:

  • I grow microgreens in seed trays or mushroom crates lined with newspaper.
  • I grow salads and herbs in smaller pots – either window boxes or small plastic buckets (10 litre / 2 gallons).
  • I grow larger leafy veg and roots in 10 or 20 litre (2 – 4 gallon) buckets or  the large plastic supermarket veg trays that hold 50 litres (10 gallons).
  • I grow chillies in 10 litre buckets, tomatoes in 20 litres, peas, beans and courgettes in 20 litres minimum (40 litres is better), and squash in 40 litres or bigger.
Pea shoots and microgreens grow well in seed trays - so make a great choice for very small spaces.
Pea shoots and microgreens grow well in containers as small as seed trays – so make a great choice for very small spaces.

Your turn?

What size pots do you use, and which size works best for you?

 

17 thoughts on “What size container do I need?”

  1. I find it helps to stand blueberry pots in saucers if they are in a sunny/windy position because they require constant dampness. I do concentrate on ornamentals at work because the place has to look nice for visitors and I am only there 3 days per week, I often mix edibles with the ornamentals though. I’m going to try doing more of that this year because GYO has become so popular. I have grown small pumpkins and squash in the pots, but not yet courgettes, mainly because they tend to become such enormous plants – and if they get mildew they look awful! I am probably going to try them this year though.
    I would never recommend lining our pots with plastic, it stops the roots from binding on to the pot walls (see my previous comment), is likely to impede drainage, means that less oxygen reaches roots, and encourages slugs and vine weevils. I think people need to consider the foliage/root balance of their potfuls instead of worrrying so much about the material of the walls. In my experience people expect large plants to thrive in small pots – if you look at the volume of leaf and compare it by eye to the volume of compost you can see why some potfuls never seem to be happy. This is hard to explain without being able to draw some sketches!

  2. Perhaps the biggest issue with containers, is the high temperature the soil can reach. Having the container shaded either articically or with plants, will reduce the stress dramatically. The choice of container, again is important. I cant find it on the internet, but there was a trial a while back that tested the various different container types. Black plastic, surprisingly was not the worst as it radiated heat as well as absorbed it. Clay I believe was the worst.

    The same can be said to be true of protecting the pots from the excesses of the cold. It would seem logical that wood might be the best material, as it is a poor themal conductivity. The greater the volume of compost will also provide a better buffer (likie the ground) to extremes.

    There is alwatys a temptation to over water plants in pots, though this in fact, can cause more problems than it releaves. Watering early morning when the compost is cool, reduces the speed at which compost heats up and there by keep the soil temperature at a level where the roots can function. A sodden compost at a high temperature, not only removes air available to the roots, but will also prevent the compost cooling as quickly at the end of the day. Perfect conditions for root dieseases and reduction of nutrient and water uptake.

    When watering pots, you should only really supply as much as the plant will need in one day, and in the ornamental industry, research has shown that watering 25% less than the rainfall received in the previous 24 hours, is the most efficient method to follow.

    Alternatively, use a water resevoir and take away the worry!

    1. Thanks for sharing your experience, Morris – I’d be fascinated to see the trial of different container materials if you come across it again. I was planning to write a post on the pros and cons different container materials soon – and it would be great to back my observations up with some hard facts! About watering pots – the other advantage of watering pots in the morning, of course, is that it is less conducive to slugs which love evening waterings!

      1. Cheap, thin terracotta may not be a good insulator, but sturdy, good quality terracotta of the correct porosity works beautifully. I find that the fine roots of plants grown in Whichford terracotta (and here I must declare that I am the gardener there) bind themselves to the terracotta, so that the pot and rootball almost become one – this prevents the compost from shrinking away from the pot walls (as it does in plastic pots), so that it is easy to water the potful without the water running uselessly down the gap. I can honestly say that I have not had problems with plants getting heat stress in our pots – but correct plant choice and positioning is important too…

        1. My experience with sturdy terracotta is quite limited so its invaluable to learn from your experience, Harriet. My experience with terracotta is that it can dry out rather quickly – or is this just the case with the cheap stuff? I did try some blueberries in large, very good quality terracotta pots last year and they did less well than they did in the plastic pots. Although there may be other reasons why this happened (eg I moved them to a more sunny spot as apparently it improves the flavour of the fruit). I’d be very interested to know if you would you grow a water hungry plant like a courgette in terracotta?

          I’ve occasionally lined terracotta with plastic to reduce the water loss – is this ever something you’d recommend?

  3. You are spot on – it is much easier to look after a large container than a small one and yields will be better. My tip (I have 200-500 pots on display all year) is to group pots together – creating a more humid microclimate – thus the pots dry out much less quickly. This way you can also insert pots of flowers among the group to attract pollinators and move them to hide empty spaces where crops have been harvested.

    1. Thanks for sharing your experience and tips, Harriet. I love growing a few flowers in between crops, too. And very interesting observation about grouping pots to create a humid microclimate – that’s a great idea. I know that some gardeners say it’s important to ensure there is a good air flow between plants to help prevent pests – do you ever find this is an issue when you place lots of pots together?

      1. I know that’s potentially an issue, but the pots don’t need to be crammed together to make a difference, in fact because our pots are decorative I arrange them so that they can all be seen, this often involves putting some of them up on brick plinths or walls. It’s trial and error, really, and of course with containers it’s easy to put spacing errors right! I also think that because plants are raised up in pots the airflow can actually be better than on the ground. A lot of gardening involves getting to know your own patch – where the stagnant, snaily corners or the wind tunnels are – and making adjustments to optimise the use of your space.

  4. This website is a true inspiration! Please, keep it going. I’m interested to find out more about your wooden boxes. Are the water reservoirs on the bottom fully water tight and are they connected to your water butt? Also, for a similar size balcony garden in your experience would you say a 50 litter water butt connected to a down pipe would be big enough.

    1. Yes, the water reservoirs in the wooden boxes were fully watertight – they were basically empty plastic boxes linked together with plumbers piping, which in turn were linked to the water butt. If you buzz me an email I can send you a link to the design. About water butt size – I guess it depends on a few things like how much rain fall you get in your area, how regular it is and how big a roof area you are collecting from. Water is always handy to have so if you can fit / afford a slightly larger one (or two linked together) it might be useful. But a 50 litre could be enough (much, much better than no water butt!) – maybe give one a try and see how it goes? (The one on my balcony was 80 litres – which was enough for most of the year).

  5. I always find the bigger the container the better (within reason) and your analysis explains very clearly the reasons why. Deep metal planters are often available from garden centres and DIY stores and these are lighter than terracotta and last longer than wooden containers. They can add up to a united display on a roof space.

    1. Hi Mark,
      very interested in your self-watering containers and would appreciate the link as you mentioned..
      Thanks
      Rick

  6. Very topical, I’ve just been outside looking at what’s survived the cold temperatures & planning which edibles to grow in which pots/bags…
    My challenge is finding veg/herbs/fruit that do well in containers that are mostly in the shade. Do you have any recommendations?

    1. Most leafy veg usually do OK in less sun – so things like salad leaves and oriental leaves (like pak choi) usually do well. Also many herbs do well, particularly things like mint, parsley, chives, sorrel, and lovage. Even some of the more Mediterranean herbs like rosemary and bay will do OK with just a few hours of sun. As long as you don’t have total shade (you really need a minimum of 2- 3 hours a day) all these things should do OK. I’ll be putting together a more comprehensive list in the near future.

  7. This is a really useful post – thank you. However, I was sorry to see the Earthboxes are made of plastic and contain a peat-based growing medium. Do you think it is essential to used peat in containers? I really try to avoid it if possible.

    1. Thanks for sharing these thoughts, Joanna, important issues. Like you, I don’t use peat in containers, either, and don’t think it’s necessary. The Erathboxes I’ve seen for sale have always been empty – so you can choose which compost to use. I usually use municipal compost or New Horizon peat free – and add some loam if I can find it. Plastic is also a thorny issue and, to be honest, I’m not too sure where I stand on it. On the plus side for Earthboxes, the plastic used is very strong and resilient (as well as being ‘food grade’), designed to last for ten years or more.

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