Soil depth experiment 1

There is a big trend at the moment in recycling containers to use in the garden (we’ve already touched on it with recycled food containers used for raising seedlings). There is also a large range of containers you can buy – from cheap plastic pots right through to enormous designer urns. What you choose is as much down to your budget as it is to your tastes, but all containers need to hold a suitable volume of potting compost and retain water whilst allowing any excess to drain away. If you are recycling containers to use for food plants then be sure that they’re clean and that they weren’t used to store anything toxic in their previous life. And remember that not all plastics are UV stable – some degrade when they’re exposed to sunlight.

Some plants are more suitable for container culture than others – those that don’t mind having their roots confined, and those with small root systems and a tolerance for drought are the most suitable. Larger plants and those that need a lot of water are usually fine if the container is large enough and their water supply is regular, but there are some plants that just don’t thrive (or are not productive) in containers and it’s usually because they have large root systems or don’t like being contained.

When you’re choosing your container you also need to think about what it’s made from. Plastic containers can be ugly, and many gardeners avoid them, but they do retain water well – useful in hot weather and for plants that like to keep their feet wet. Terracotta pots are more expensive, but look nicer. They allow evaporation through the sides of the pot and so are harder to keep well watered, but are good for plants that live life on the dry side. They are much heavier, which is a consideration for balconies and roof gardens. The final point to note with terracotta and similar materials is that they’re not entirely weather-proof and can be damaged by frost over winter.

Unless you’re catering for plants that need to remain submerged (i.e. creating a pond environment) then your containers need drainage holes so that excess water can drain away when it rains. They’re usually in the bottom of the pot, but can be part way up the sides to retain a shallow layer of water in the bottom.

Gardening advice often recommends putting ‘crocks’ (broken pot shards) into the bottom of containers to ‘improve drainage’. I tried this when I started gardening, and all I got was a cut finger when I emptied out the pot at the end of the season. Some people use chunks of polystyrene for the same reason – then you get polystyrene in the compost, which is horrible. In fact, there is scientific evidence that putting chunky materials in the bottoms of containers actually makes the drainage worse and can lead to waterlogging. At the very least it reduces the volume of compost available to plant roots.

Grow bags are commonly used for growing tomatoes in the UK, and they’re usually laid flat so that two or three plants can be planted into holes cut in the top. Drainage holes in the bottom allow excess water to drain away. This is not the easiest way to grow tomatoes, which like a lot of water and feed and don’t really enjoy life in such a shallow volume of soil. A better way is to cut the bag in half and arrange those halves vertically, so that each tomato has a deeper (and separate) root run for the same volume of compost. You can also buy special tomato pots that are used as an extension to grow bags. You lay the bag out as normal, make your holes and then put the tomato pot into the hole. The tomato is planted in the pot, and benefits from a deeper root run; it’s also easier to water into the pot.

Growing lettuce in a bag

Of course, there’s no reason you can’t make your own growing bags out of a strong plastic bag and homemade compost (or your chosen potting mix) – but avoid using degradable bags as they may fall apart before the end of the season.

The benefit to grow bags is that they allow you to grow tomatoes in the same space every year without having to use the same soil (which rapidly causes a build-up of pests and diseases). If you have the space you could try planting into straw bales instead (it should also work for cucumbers, melons and other greenhouse crops). I haven’t tried it yet, but there’s a lovely article on the subject by Christopher McCooey in the Telegraph. The basic idea is that you add water and nutrients to the straw bales so that they start decomposing. Their internal temperature rises, which helps your crop, and then you scoop out planting holes and fill them with compost. You plant into the compost and then care for your plants as normal. After one or two seasons your spent straw can be recycled as mulch or added to the compost heap. It may well be worth trying if you have easy access to straw bales.

Another special case is hanging baskets, which suspend plants in a small volume of compost up in the air and well away from the soil. Traditionally they are lined with sphagnum moss, which grows in peat bogs – when it dies it decomposes slowly to become peat. In theory, sphagnum moss is a renewable resource, but in practice it is often over-harvested. It may be possible to grow your own; one of my Australian correspondents does just that in a shady spot in her garden. I am trying it myself, although I don’t have much shade. Whether it’s easy (or even possible) to grow enough to line a couple of hanging baskets every year remains to be seen. If you have a patch of grass then you can use lawn moss instead – recycling a waste product.

In any case, there are plenty of peat-free options for hanging baskets. Ready-made liners are made from coir (sometimes processed into green ‘coco moss’), wool that is a by-product of the wool industry or even compressed paper. You can recycle old woolly jumpers if you want to – it would probably take several seasons for them to decompose to the point where they can no longer be used. If you’re a crafty person you could even knit or crochet your own liners, out of suitable yarn or garden twine. There used to be a pattern on the internet, but it seems to have disappeared. If anyone has one they would be willing to share, then let me know! I imagine it could be quite a simple pattern; I may give it a go myself as a winter project. (Kate Bolin has a lovely pattern for little knitted hanging pouches.)

Whatever you use as a container, and whatever you fill it with, feeding and watering your plants will be your most regular tasks.

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