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Debunked: crocks in plant pots helps drainage

Pot crocks

We seem to have caused rather a controversy in the normally sedate world of gardening by debunking a gardening myth that’s been around for years…

Turn on any gardening TV show or open any gardening magazine and you’ll find gardeners religiously putting a layer of ‘crocks’ at the bottom of their patio pots before filling them with compost.

A pile of crock

The idea behind this activity was to improve drainage. But Which? Gardening research found that crocks made no difference to how well our plants did. Research by soil scientists has proved that water does not flow freely from fine-textured materials such as compost into coarser material such as crocks. In fact, it only does this when the compost above the crocks is saturated. So, in wet summers, crocks can prevent water draining out of the pot and do more harm than good.

Yet, so many of us do it. We found that 62% of Which? Gardening members always use crocks in large pots – only 6% never do. And 71% of crock-users opt for broken terracotta pots. But with plastic pots now being more commonly used than terracotta ones, it becomes an expensive business breaking perfectly good pots just to use as crocks.

Will you still use crocks?

So what will you do this spring? There is an argument that crocks help reduce the volume of compost you need to fill pots and so you could save you money. Using broken polystyrene instead of terracotta crocks can also help to reduce the weight of pots, which is useful if you struggle to carry them or are going to put them on a balcony or somewhere else where you don’t want excess weight.

For me, my nostalgic side will miss the ritual of finding crocks and putting them in, but debunking myths is what makes working for Which? Gardening so fascinating. Therefore, if not using crocks is one less job to do and it’ll also help the success of my pots, then I’ll be happy to give it up.

Do you put crocks in plant pots?

Yes (53%, 591 Votes)

I did, but will stop thanks to Which? Gardening's research (28%, 318 Votes)

No (19%, 216 Votes)

Total Voters: 1,125

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Comments
Member

Using crocks helps prevent compost escaping through the drainage holes and by adding weight it can help prevent pots falling over if the plant makes them rather top heavy. That’s my argument for continuing to use them.

Member

Can the “crocks” be recycled? Or will they just end up in the general rubbish? So using them at the bottom of flower pots would be a good way to avoid unnecessary landfill use.

Member

My crocks have probably been reused many times because new ones are less easy to obtain thanks to the move to plastic pots. I have a plant pot with my stock. No doubt you have heard of the term: “A load of old crocks”. 🙂

Member

I stopped using crocks 25+ years ago. Instead, I use polyester wadding (the stuff my wife uses for stiffening and backing in sewing). It’s thin, so doesn’t steal room from the growing medium, it stops the groewing medium falling through the drainage holes and its capillary allows for good drainage. It is resistant to nasties crawling into the pots through the drainage holes too.

Buy the cheapest, thinnest wadding and simply cut a small circle (or square) to fit the bottom of the pot.

Member
Christina says:
28 April 2014

This sounds like a brilliant gardening tip. Thank you.

Member
Steph says:
3 May 2014

Yep – I think so too, and so will I! Thanks

Member
Flibertigibit says:
4 May 2014

Similarly for many years I have used cut up pieces of cheap versions of those checkered throw away J cloths cut into roughly the right size and usually double thickness. I especially do this for plants I know will be moving into bigger pots soon or planted out. It does the job well and seems to be biodegradable so I don’t need to bother disturbing the roots, just leave it to rot away.

Member

Old j-cloths sound like a good idea to me too. As you say, they’ll eventually biodegrade (rot), so many be even better than wadding.

Member
Margaret Mccadden says