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Are gardeners wrong to put 'crocks' in plant pots?


By alextb


BBC Magazine Monitor

For centuries, gardeners have put shards of pottery – “crocks” – at the bottom of plant pots to increase drainage. But a new study has debunked the tradition, writes Tom de Castella.

Crocks in pots are an article of faith for gardeners. A piece of crockery in the bottom of the pot aids drainage. It allows water to run off more quickly than soil would and prevents compost from clogging up the holes at the bottom of the pot. That at least is the age-old wisdom handed down from one generation of green-fingered sages to the next. Gardeners’ Question Time, Monty Don and Alan Titchmarsh have all endorsed the tradition.

But a study by consumer magazine Which? suggests it’s a myth. Researchers planted 40 pots each with five “Million bells trailing yellow” – a flowering plant prone to root rot in saturated soils. Permutations involved plastic pot, and terracotta pot, and with either saucers or no saucers. Half got crocks, half did not. The plants were recorded for “vigour and flowering impact”. The magazine found that the crocks “made no difference to how well our plants did”.

You might think that the bigger gaps where soil meets bits of broken crockery would allow more water to filter through. But this turns out not to be the case, some argue. Guy Barter, chief horticultural adviser at the RHS, says a crock is actually likely to worsen drainage by creating a block. It’s better to have a layer of sand underneath soil that will allow water to drain into it and later be sucked up by roots if needed. The only minor points in favour of crocks are that they might block drainage in hot weather, and also save money on compost. In most cases, people would be better off omitting them, he says.

Like many gardening “tips” it probably owes more to Victorian fashion than practicality, says Matthew Biggs, a panel member on Gardeners’ Question Time. There was something comforting about re-used shards of terracotta performing magic inside the pot. “It’s always sad when a tradition gets blown away by modern science.” But many will probably ignore the science, and carry on with this “intuitive ritual” that is part of gardening heritage, he says.

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I always put "crocks" in the bottom of flower pots...I thought it was to keep the drainage hole free...and I´ve had no problems upto now.

24 Apr, 2014


It was done to stop the compost falling out through the hole. Look at really old pots and the hole is generally a lot bigger than modern pots.

It also makes it much easier to unpot a plant because you have something solid to push against.

24 Apr, 2014


I have not 'crocked' a pot for many, many years. If the pot is on a hard standing then I have found no problems, if it is sitting on soil/grass or in a plunge then the lack of a crock enables a continuity between the compost and outside medium for moisture transfer.

24 Apr, 2014


I have run out of terracotta crocks so if the drainage hole needs covering enough for the compost not to fall through the hole I use one or two flat little stones. But i agree, modern smaller plastic pots don't need any.

24 Apr, 2014


I save the broken bits of pot to cover the holes in the pots rather than drainage.

24 Apr, 2014


I don't use crocks in planters or pots. In large planters I use a flat stone over each hole and in small plantpots I use folded kitchen roll to cover the holes and stop the compost falling through. Works fine for me!

24 Apr, 2014


Used to use crocks or stones, now I use polystyrene as its lighter when lifting, unless I haven't got any then its back to the broken crocks. It works for me and I see no reason to change my method...Somewhere I saw a tip that said use spent teabags but I can't remember where I saw it....

24 Apr, 2014


I don't use any for smaller pots but for large and extra large pots I tend to fill the base out a bit with polystyrene, it reduced weight as Lincs has said and also cuts down on the amount of compost I use.
One thing I do do and it's a tip I learned here on GOY was to line the hole with jay cloth, this will stop any creatures burrowing in and making the pot their home, in particular ants.

24 Apr, 2014


I have never used crocks or polystyrene and never had a problem.

I thought posting this would grab GoYers attention.

25 Apr, 2014


Jay cloths is clever Scottish. I wonder if it even keeps woodlice out?

25 Apr, 2014


I stopped putting crocks in some years ago. I used a J type cloth until I used garden fleece which works well and can be reused if need be.

26 Apr, 2014


My dad always used spent tea bags.....I use leaf tea tho'.

1 May, 2014

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