If you’re planning to get more containers for the new growing season, you may well be asking: ‘what size of container do I need?’ There’s no straight forward answer – but here’s the information that will help you decide.
If you’re reading this post, you may also be interested in what’s the best material for containers.
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 – for everything except root vegetables. 30cm (12 inches) is deep enough for most crops. Salads and herbs will be happy in less – 10cm – 15cm (5 – 8 inches) is usually enough.
Pros and cons of big pots
Big pots have big benefits
- 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’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.
But also drawbacks
- They cost more (in both pot and soil)
- They take up precious space
- They weigh more. Weight is a particular issue if you are growing on a balcony or rooftop – you must take care not to overload the weight bearing capacity. (Check with a structural surveyor if unsure).
Pros and cons of smaller pots
Smaller pots are better 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.
The downsides are
- They dry out faster – creating more work and more stress on the plant. 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. However, light feeders – like most salads and herbs – will do fine.
So which is best?
If space, budget and weight is no issue, then large pots win every time (I’d probably go for 30 – 40cm deep, 1 meter long and 60cm wide – equivalent to 12 – 16 inches deep, 3 feet long, 2 feet wide).
But as urban growing IS usually constricted by space, weight or budget (usually all three!) a mix of sizes is often the best solution. Here’s what I recommend you try – but as always, experiment to find what works best for you:-
Choose smaller pots for your salads, Asian greens and herbs. Cheap plastic window boxes 15cm (6 inches) deep, 20cm (8 inches) wide are fine. Plastic trays from grocery stores or polysterene boxes from fish mongers do the job equally well.
Choose medium sized pots – at least 30cm (12 inches) deep and 30cm (12 inches) in diameter – for larger leafy veg like chard or kale, baby root vegetables like carrots, beetroot or turnips, and for the smaller fruiting vegetables like chillies or small hanging basket type tomatoes. Old plastic food waste buckets, large empty cooking oil tins (see pic below), and the buckets on flower stalls (often available free) are good recycled options.
Choose large pots – at least 30cm (12 inches) deep and 40cm (16 inches) in diameter (50cm or 60cm diameter is even better) – for larger fruiting crops like vine tomatoes, aubergines, peppers, courgettes and squash, bigger root crops like potatoes. I also like to grow peas and beans in large pots. Old 50 litre recycling bins are a perfect size. Old hessian sacks or compost bags can also be used – great for potatoes. If you’re thinking of investing in your growing, check out Earthboxes, (NOT an affiliate link) a good size for most veg.
What’s your experience?
What size pots do you use, and which size works best for you?