1 PET1: Polyethylene Terephthalate marked with a 1 on the triangle. Very commonly recycled, can break down when exposed for long periods of time to light or heat.

It’s the stuff drinks bottles are made of and it breaks down too easily to withstand sunshine and weather.

2 HDPE: High Density Polyethylene (Polythene) doesn’t break down easily, resists UV rays and very heat tolerant, coping with -100 to 80C – one of the most common plastics used in the garden because of these properties.

Used in: most black, brown and green rigid plant pots; seed trays; the containers you buy pesticides, herbicides and fertiliser in; insect-proof mesh

3 PVC: Polyvinyl Chloride Used in plastic pipes and irrigation. Most contain chemicals known as phthalates, helping the PVC to be more durable, flexible etc. But phthalates are very harmful to humans.)

4 LDPE: Low Density Polyethylene (Polythene) Single use plastics used in things like plastic produce bags and bin liners. It came along after HDPE and shares many of the same characteristics – so very safe in a wide range of températures and doesn’t leach into the soil.

Use in gardens: Single-use packaging around mail-order items

5 PP: Polypropylene Used in products that require injection moulding like straws, bottle caps, food containers. Not as tolerant to heat as HDPE or LDPE, generally safe for use with food and the garden.

Use in gardens: Compost sacks; some more flimsy plant pots (eg seedling modules); Horticultural fleece is made from woven polypropylene.

6 PS: Polystyrene One of the most widely used types of plastic, but one of the most harmful to the environment as it breaks down very quickly into very small particles, and tends not to last very long.

Use in gardens: Bedding plant trays, pots, labels and packaging for mail order plants

7 Polycarbonate (this actually means any plastic other than those listed above – but usually polycarbonate or polylactide). Polycarbonate is the most harmful plastic we have ever created: proven repeatedly to leach BPA (Bisphenol A) –shown to cause reproductive problems in animals and linked to cardiovascular disease and diabetes in humans.

Use in gardens: Plastic non-breakable greenhouses and cold frames.