Bio-based alternatives to plastic plant pots

In recent years, plastic pollution has hit the headlines as a major environmental issue. While gardening is an outdoor activity involving organic material and natural products, the uncomfortable truth is that gardeners use a lot of plastic.

At the start of the 2018 series of the BBC show Gardeners World, presenter Monty Don acknowledged this. Talking about his own garden, which is used in the show, he said: "One of the things that has really horrified me looking at the garden over this winter is the amount of plastic that we're using here, we have plastic pots, we have plastic seed trays, almost everything I buy is wrapped in plastic."

Pots are one of the most common plastics in the garden. In the UK alone, it is estimated that around 500 million plastic plant pots are used every year. And a survey by consumer magazine Which? found that the average British gardener has 39 plastic plant pots cluttering their shed, greenhouse or garage.

Of course, you can look after the pots, use them more than once, and eventually put them out with the recycling. But unfortunately, it isn't quite that simple. They are often not easy to recycle, and worldwide less than 10% of plastic waste is recycled.

It is possible, however, to buy bio-based pots. These are made from fibrous bio-based materials such as wood pulp, rice hulls and cow manure that are pressed into the shape of a plant pot. Most are biodegradable and can be planted with the plant, or thrown in the compost, once finished with. Some – such as those made from rice hulls – are rigid and can even be used multiple times, over a few years.

One disadvantage of bio-based plant pots is that they tend to be more expensive than plastic ones. Currently, on Amazon.co.uk, for example, you can get 100 8 cm wood pulp pots for £13,99 (€15,62), while 100 similar sized plastic pots will cost you £10,88 (€12,15).

However, a recent survey by Gardeners' World magazine, in the UK, found that 85% of its readers wish to use less plastic, and 66% would be willing to pay more for goods that reduce their plastic use. Research in the US found that people are willing to pay more for non-plastic pots. This suggests that there is an appetite for alternative pots, even if more expensive. But naturally, after more than 50 years of plastic pots, gardeners will be concerned about how well these alternatives work and possible negative effects on their plants.

Research on bio-based pots and plant growth is limited, but in 2015 a special issue of the journal HortTechnology looked at alternative containers for growing ornamental plants.

Two US studies compared the growth of different plants in plastic, bioplastic and bio-based pots – made from coir, manure, peat, rice hull, straw and wood pulp. One found that in greenhouses there was no difference in growth between plants in bio-based and plastic pots, concluding that bio-based pots were suitable alternatives to plastic. The other found no impact on plant establishment or growth when planted outside in bio-based pots, compared to plants that had been started off in plastic containers.

A research review also found that most trials had seen little difference in plant growth between plastic and bio-based pots, but there were a few exceptions. "In other research, plants produced in conventional plastic containers have greater growth," the authors write. They suggest that this inconsistency may be due to increased water loss through the walls of bio-based pots – which could affect plant growth – and highlight a few trials that have shown that plants in some alternative containers need more water.

Read more: www.allthings.bio/bio-based-alternatives-to-plastic-plant-pots/