Pots and containers for indoor growing (Part 1)

Hello and welcome to this presentation about choosing suitable pots and containers for indoor growing.

So we need to first look at what a container needs to do for plants that are growing indoors. It needs to hold onto compost and stop it washing out. It needs to contain that compost in quite a close confinement so that the roots can grow into it. The pot also needs to help retain moisture in the compost around the roots of the plant. Although we do need to have drainage holes in the base of the container to allow any excess to drain away, so the plant isn’t sitting in really saturated conditions all the time.

We need to allow air into the compost in some way through the top of the pot, but also in combination with the drainage hole at the bottom where water drains out and that sucks in air through the top of the container. The container also needs to provide enough weight to support the top growth of a plant. And that’s particularly important for tall plants that make a lot of leafy growth. The container needs, in most cases to exclude light from the roots because in most cases roots grow in dark conditions underground, rather than in bright light. The exceptions to this being epiphytes and many orchid house plants, which need light exposure on their roots.

So in that case, then the container needs to be clear. We also need a container to insulate the roots as much as possible from wide fluctuations in temperature. So, again, roots generally are used to being underground where conditions are fairly stable and cool. And we need that container to emulate those conditions as well. And we need the containers to be durable and reusable, and it needs to be able to be cleaned if we’re going to do that. Now,

the sorts of materials that you can use for containers, for growing indoor plants are quite wide. Unglazed terracotta pots are probably the most traditional, and because they’re unglazed, then they tend to take away the moisture from the compost so they wick it away, absorb some of that moisture, and it evaporates from the surface of the pot, which keeps the balance of water quite well in the pot, in the container, it stops the container becoming waterlogged very easily, but it can wick away too much moisture and cause the plants to become dry. They’ve often got one large drainage hole. And one of the downsides is that they’re breakable.

But fortunately, they they do insulate the plant from extremes of heat and cool quite well. The same is true of glazed terracotta, but of course, in the case of glazed terracotta, then the sides of the pot are not porous. They don’t wick the moisture away. So it needs to be watered quite carefully. Wood is possible for some containers, for indoor plants. It can have some porosity, it can absorb some moisture away from the plants, but it normally gets saturated and then doesn’t wick any more moisture.

It’s a good idea in wooden containers to have multiple drainage holes to make sure that the plant doesn’t become waterlogged. And it’s easy to make bespoke containers using wood for use indoors. They’re robust, generally unbreakable, although they are liable to rotting. And wood is a great insulator from heat and cold. Metal, however, is not a good insulator from heat and cold, and it transmits heat. So if the sun’s shining on a metal container on a windowsill, for example, then the root environment can heat up very quickly, making it not very good for house plants.

And also equally on a cold windowsill, frost can radiate through glass in the winter, and that can also penetrate through the metal very, very readily and into the plant roots. Plastic, generally speaking, can be extruded into all sorts of different shapes, various colours, and they’re impervious to water and long lasting and don’t rot. So they make good containers. But we do need to make sure that we reuse as much plastic as possible, as many plastic pots as possible, and not add to an already plastic-filled world where possible. Clear plastic versions are available for epiphytes and also orchid roots that need light as well at their roots, as well as moisture.

They have medium insulation properties, so they’re not particularly good at retaining heat or insulating plants from heat. If heat shines through a window onto a plastic pot it can heat up the compost inside quite readily. There are also fibreglass and resin pots. These are robust and durable, quite similar in a way to plastic pots. But unlike plastic pots, which can be degraded by exposure to light and making it go brittle, fibreglass and resin are much more light stable. They are quite insulative and that means that plants are protected from extremes of heat and cold. And then lastly, you may find some glass containers in the forms of bottles and vases and glasses.

Generally speaking, though, for bottle gardens, these don’t have drainage holes in them. So you need to be quite careful about how you use them for growing plants in. And also bear in mind that they’re easily broken. They could be useful inasmuch as they allow light through to the roots of epiphytes and orchids, but they do transmit cold and heat very readily. So, again, we need to be careful in their use.