Rocks in bottom of pot for drainage?


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Will adding small river rocks to the bottom of a pot improve drainage or will it actually retain more water?
 
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it will improve drainage. its interesting how water can worm itself around through rocks. another good thing for that is wine corks, a little lighter, will do the same.
 
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Interesting article here on crocking pots
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.
 
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Digressing a bit but on the subject of drainage. We put bits of broken pot at the bottom of our dozen or so ceramic patio pots. All ours are on plastic pot movers. I drilled a hole in the middle of these, so that surplus water doesn't collect in them during the winter. But in the Summer I put a dab of silicone over the hole so that surplus water can sit there and keep the plants from drying out. If on hot days I see any without any water in them I know it's time to water that plant.
 
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I don't add rocks to pots, I use the perforated metal sheets sold as car body repair material. That stops worms from getting into the pot from below and keeps the compost from falling out.
 
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Interesting article here on crocking pots
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.
Seems a more scientific test would be to simply pour equal amounts of water into each pot and measure the amount that drains out. Too many factors in the test mentioned to draw conclusions.
 
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Seems a more scientific test would be to simply pour equal amounts of water into each pot and measure the amount that drains out. Too many factors in the test mentioned to draw conclusions.
The all point is how the plants in the pots perform most are against crocking now like this item

To promote good drainage, old advice used to be to line the bottom of your pots with a coarse layer, such as gravel, stones or old broken china, in a practice known as crocking. Crocking was supposed to encourage water to pass down from the potting mix into the gaps in the coarse layer below and out through the drainage hole.

It sounds so plausible doesn't it? Maybe that's why so many people still do it.

Yet soil scientists have known for years that crocking doesn't help drainage. In fact, it can hinder it.
 
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Hello,

Fundamentally, good drainage is down to a couple of factors. Ideally, compost used straight from the bag needs to be modified through the addition of either horticultural grit or perlite (messy). For woodland species I use pine needles and fine composted bark in addition to grit. This opens up the structure of the potting medium and aids the flow of water through the pot and encourages good root development and growth. You can adjust the ratio based on the requirements of the plant. The second factor, and which the original post relates to, is the efficient egress of water from the bottom of the pot (prevents stagnation). Some of the very old clay pots which I use (with great care - over 100 years old) have a huge drainage hole which, if not crocked, would allow the compost to fall out of the bottom.

Martin.
 

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