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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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I have over 50 pots in my garden and have allways used something to aid drainage, I have used gravell oldpolystyrine pot holders broken up and the usual crocs, my belief is without something in the bottom pot holes get clogged up with compost ,consequently the excess water cannot drain away, so until somebody proves to me this isn’t the case I shall carry on as before

Well this year I brought raised 80 Pelargoniums (for a wedding) potting into 13cm plastic pots. As an experiment, I only lined the bottom of 40 pots. They were all bottom watered using rain water. They all thrived.

Not exactly a scientifically conducted experiment, but sufficient for me to believe that maybe for annuals, messing with crocks is a waste of time.

brianca says:
3 April 2015

I have stopped using crocks and have changed to gravel and found that its weight helps keep pots stable and gives improved drainage.I am also an”old croc”