Plastic substitutes

If not plastic, then…. what?

So far I’ve been concentrating on what to do with the plastic you’ve already got.

But once you’ve taken the pledge not to buy any new plastic for your garden (and done your best to fend off the plastic that keeps trying to get back in) you still need pots, and seed trays, and hanging basket liners. So if not plastic, then what?

Smaller pots – anything up to about 7cm – are easy. You can make them yourself: save your loo rolls, make newspaper pots, or use a soil blocker. Small plastic pots and module trays were the first things I got rid of in my garden: I no longer use them as I find the alternatives so much better. I’ll be detailing how I did it soon on this very blog.

Larger pots, though, are tricky. You can’t make them yourself: so you have to buy them in. And most of the pots you’ll see offered for sale at sizes 10cm and above are plastic.

That’s not to say there’s no alternative to plastic pots: actually, there are loads, they’re just quite difficult to find. The stranglehold plastic has over the horticultural industry is loosening off, just a teeny bit, and most garden centres now sell at least some biodegradable pots. But if you look into it more closely, the choice is actually quite bewildering. I have found just under a dozen different biodegradable materials currently used as a replacement for plastic in gardening products. Here’s the list:

  • coir (coconut fibre)
  • miscanthus
  • spruce wood
  • bamboo
  • rice husks
  • straw
  • cow manure
  • starch
  • cellulose
  • cardboard
  • terracotta clay

Some of these sound like they might be the same thing, but nonetheless – it’s quite an impressively varied choice.

Why we are still using so much plastic when there are so many other types of pot out there I’m not entirely sure. Part habit, I’m sure; but also because biodegradable pots are definitely more expensive. This is mainly because most biodegradable pots, ahem, biodegrade; so they don’t last very long and need replacing each year as they are planted along with the plant. That’s not the case with all of them, though: clay pots are the obvious example of a long-lasting biodegradable pot, and there are others which claim a life of at least 3-5 years.

The clincher for me, though, and one that justifies the extra expense is that quite a few biodegradable pots are an improvement on plastic. When plant roots can breathe (as they cannot in plastic), when they can grow through a material rather than being forced to circle round and round (pot-bound plants are a thing of the past when you grow in many biodegradable pots), and most importantly of all when container and plant can go into the ground together with no need for root disturbance – that means a happier plant that’s more vigorous, healthier and quicker to establish in the garden. I can bear witness to this myself: my results, especially at the beginning of the year when I’m sowing, pricking out and transplanting hundreds of plants, have noticeably improved since I stopped using plastic.

Not all these advantages apply to rigid biodegradables like clay or bamboo, but you still keep some. I find when growing in clay pots that the plants seem to appreciate the increased exchange of air and moisture through the sides of the pots, and though they dry out more quickly they also wet more thoroughly than plants in plastic pots, as the clay absorbs the water as well as the compost. That means you don’t get that effect of water running down the sides between rootball and pot before draining out the bottom and leaving the roots as bone dry as if you hadn’t watered at all.

The more I grow in biodegradable containers the more I like it. But having tried a few different types in a rather haphazard way over the last few years, I’m also aware that they are not all alike. There’s a big difference between growing in a floppy coir pot and a rigid terracotta pot; and there are other considerations too. Rice hulls have a very different environmental footprint to cow manure, for example.

So I am going to be spending the next few weeks collecting together information about as many of the biodegradable alternatives out there as possible. I’m also going to get my hands on a few samples of the pots in question and put them through their paces. The result, I hope, will be the most comprehensive analysis yet of exactly what it’s like to grow your plants in non-plastic materials; which are the best, which don’t perform so well and which you should be using in your garden.

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Research

The plastics in your garden

There’s a huge range of plastics in common use in the garden. Here’s the breakdown:

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.

Used in: Practically nothing in the garden. It’s the stuff drinks bottles are made of and too unstable for most uses as it breaks down to easily to withstand sunshine and weather.

HDPE: High Density Polyethylene (Polythene): marked with a 2 on the triangle: 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

How to avoid: Use biodegradable pots; use wooden seed trays; make your own pesticides, herbicides and fertiliser from the plants you grow; and I am still experimenting with alternatives to insect-proof mesh. Calico is looking expensive, but promising.

PVC: Polyvinyl Chloride: marked with a 3 on the triangle. 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.)

Use in gardens: hosepipes

How to avoid: rubber hosepipe might seem a good alternative, but many are synthetic rubber which is basically plastic. Better just not to use a hose: use a metal watering can instead.

LDPE: Low Density Polyethylene (Polythene): marked with a 4 on the triangle. 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

How to avoid: Buy from nurseries and garden centres or find a supplier who doesn’t pack in plastic (easier said than done…)

PP: Polypropylene: marked with a 5 on the triangle. 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: Some more flimsy plant pots (eg seedling modules); Horticultural fleece is made from woven polypropylene.

How to avoid: Use newspaper pots instead of modules; wrap plants in hessian and straw instead; or just avoid growing particularly tender plants.

PS: Polystyrene: marked with a 6 on the triangle. 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 and packaging for mail order plants

How to avoid: Raise your own bedding plants, or buy from a supplier who doesn’t use polystyrene trays. Buy from nurseries and garden centres or find a supplier who uses biodegradable cornstarch packing instead.

Polycarbonate: marked with a 7 on the triangle (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.

How to avoid: Use glass instead.