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Growing in Containers

Article by Dave Hamilton

from Grow Your Food for Free (well, almost)


Container growing has become more popular in recent years and seed companies have cottoned on to this by selling ‘patio’ varieties of our favourite vegetables. Some of these, such as the patio salads, can be a bit of a false economy, as most plants only grow to the size they are allowed to. I’ve found that conventional varieties of salads actually do better in containers than specific container seed, usually for half the price.

Tomatoes spilling from a hanging basketThere are exceptions to this rule, and growing compact dwarf beans as opposed to climbing French beans makes perfect sense if space is limited. Consider each seed on its own merits and go for specialist ‘container’ varieties only if they really do look like they are worth the money.




Large ‘tonne’ or ‘dumpy’ bags (builder’s bags) make perfect planters for potatoes and are near-identical to bags on sale doing exactly the same job! Alternatively, a large plant pot will work just as well. Plant three to four seed potatoes in each dumpy bag or pot and cover with soil. As the plant grows, cover the foliage with soil, leaving some of the leaves to poke out from the surface. Keep repeating this step as the potatoes grow until the bag is full. To harvest, roll the bag down.

What type of container?

Suitable containers and where to get them
Type of container Where to get it from Examples of what to use it for and extra instructions
Baby baths Freecycle, parents of no-longer-small children. Courgettes, dwarf beans. Drill holes in base.
Builders' / dumpy / tonne bags (woven sacks) Builders, landscape gardeners. Potatoes.
Old bathtubs Skips, recycling centres.

Almost anything - including tomatoes, cabbages and grapes. You will need to add a layer of free-draining material such as straw to the base.

NB Be prepared to take it with you when you move if you have an allotment or live in a rented house, as the next owner might not want it there!

Olive oil tins, 3 litre (0.6 gallon) or 5 litre (1 gallon) Home, small restaurants and cafes. Chillies, tomatoes, peppers. Wash thoroughly before use.
Plastic catering pot (mango chutney, mayonnaise, ice cream, etc.) Restaurants, residential institutions (e.g. old people's homes, catering colleges). Tomatoes, peppers, aubergines.
Sack (hessian or woven plastic) Pet shops (old feed bags), hardware shops, restaurants and shops (rice sacks), greengrocers (potato sacks). Lettuces, cabbages, strawberries (in holes cut in sides - see photo).
Shoes Home. Basil, lettuces (i.e. small plants). Line with plastic first and drill holes in sole for drainage.
Trugs Gardeners, recycling centres. Blueberries, currant bushes, dwarf beans. Drill holes in base.






















The choice of container is really limited only by what you can find. They need to be big enough to accommodate the plant and its roots, so a 5-litre (1-gallon) tub is never going to be big enough for a courgette plant but a chilli plant will be perfectly at home in one.


Tired advice


For some time tyres have been recommended by some to grow potatoes in, but this is no longer advised, as there are issues with toxic compounds leaching from the tyres into your potatoes.


Plants in a sack


Make the most of limited space by growing in a sackThe rooftops of urban Kenya show signs of the innovation of the gardenless occupants. In order to have a supply of fresh vegetables, many of the women of Nairobi have taken to growing much of their daily vegetables in hessian sacks.

The sacks are filled with earth and seedlings are slotted in through holes cut into the sack. If you wish to try this method on your patio or on a flat rooftop, a mix of leaf mould, compost and topsoil is an ideal growing medium, with additional nutrition supplied from liquid feeds.

Cabbages naturally grow on cliff tops and cliff faces and are perfectly adapted to growing this way; other suitable plants could include salad greens, strawberries and tomatoes.



Soils for pots and containers



by Tony Kendle, Foundation Director, Eden Project

The Eden ProjectPlants in pots have to get all of their water and nutrient needs from soil that is tens or even hundreds of times smaller in volume than their roots would reach if planted out. The containers have to be watered on such a regular basis that it puts the structure of the soil under great pressure and this structure can start to break down. A normal soil maintains a healthy structure thanks to natural activity such as worms burrowing, which isn’t as effective in containers. All of this means that for best results you have to be careful what soils to use – any old stuff won’t do.


To get the best yields you need container soils with the right pH, the right fertility and the right structure. But pH and nutrition can be fixed if you need to, while structure is something you need to get right at the beginning.


Clay-rich soils can be very fertile in the garden but they rely on worm channels and the formation of clods and airways to stay healthy. In containers this structure collapses and they can become airless and toxic.


Sandy soils have a totally different structure; they are more uniform and not dependent on clods and pores. These work best in containers.


You can make heavy soils more sandy but you need lots of sand to do it – maybe twice the volume of the clay. If you scrounge sand to do this you have to rinse it thoroughly before using it, in case it’s coated in lime or salt or something else the roots won’t like.


Organic matter is great to add to pots because it helps hold water and nutrients. But not all compost is the same. Compost made from soft material such as leaves will break down quickly and before you know it the pot will be half empty – this is a useful material for containers for annuals or short-lived crops. For perennials you need a proportion of tougher material such as composted bark and twigs. This can last for years but won’t release many nutrients, so will need more feeding.


Containers don’t need drainage layers such as broken pots at the bottom. You will never find these in the millions of plants grown in pots in commercial nurseries. But it is crucial that they drain well or the root zone will become stagnant and the roots will die. Roughly speaking, soils hold water in micropores and air in the larger pores that drain freely. Think of a bathroom sponge – when you lift it out of the water the big holes drain quickly, but the whole thing remains damp. But do the sponge test for real and look more carefully. You will see a saturated layer at the bottom that doesn’t drain. This is where water is held even in large pores, by capillary action.


What you will find is that, whatever way up you hold the sponge, this layer is the same depth. This is how it works in containers too. The soils will have a layer of a few centimetres at the bottom that doesn’t drain well and will risk being stagnant. This means that the shape of pots really matters – wide shallow pots hold more water and drain less well than tall narrow pots of the same volume. Matching the right pots, the right soils and the right plants gets the best results, but it matters most for plants that will be in the pot for a long time and where good rooting is needed.

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Extract taken from Grow Your Food for Free (well, almost) by Dave Hamilton, published by Green Books.

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