Crocks in Pots for Drainage - myth smashed!

[TrialAndError]

We've been doing it wrong for decades. Apparently there is no benefit to putting stones etc in the bottom of pots to aid drainage. See this BBC article:

BBC News - Are gardeners wrong to put 'crocks' in plant pots?

[kathyd]

Well I have no idea whether it's right or wrong, but I'm amused by the statement at the end about old traditions getting blown away by 'modern science' - not sure that's how I'd describe a one-off experiment by Which magazine with 40 pots of one type of plant...

[Bren In Pots]

I stopped using crock after finding they made a cosy hiding place for slugs.

[robmarston]

If it's true, it's good news but I think I'll find it a hard habit to break.....


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[Currysniffa]

I use crocks and large pebbles in the bottom of my big pots. But I do this so I don't have to use so much new compost. If I've got old stuff I put that in at the bottom and put new in the top half.

Never thought about slugs hiding in there. Good point Bren.

[Jeanied]

You have to stop the compost falling out through the hole at the bottom with something!

[Scarlet]

If the pots are very large I use broken polystyrene plant modules. Saves my back as they are much lighter and also saves my compost. I don't bother with "crocks" for smaller pots.

[Kristen]

Well I have no idea whether it's right or wrong, but I'm amused by the statement at the end about old traditions getting blown away by 'modern science' - not sure that's how I'd describe a one-off experiment by Which magazine with 40 pots of one type of plant...

I wouldn't say it is a one-off experiment, its been known for 100 years or more than water doesn't move well between different substrate types. Folk still have difficulty with getting their head around it ... me included!

Personally, the question I want answered is "Once the water HAS moved to the crocks surely it then flows freely out of the one hole at the bottom of the pot" - so perhaps the soil-to-crocks flow rate is better than the soil-to-drainage-hole rate?

Given that "crocks are bad" for drainage (assuming we just go with the science ) I think there is a big gain using ALL the pot for compost, rather than wasting 1/3rd (or whatever) of it for extra-drainage

This from Linda Chalker-Scott a Horticulture Professor at Washington State University. I do find she bangs her drum loudly on only one side when she discusses such things, but IMHO she knows the science better than most.

http://puyallup.wsu.edu/~linda%20cha...20drainage.pdf

[alldigging]

40 pots worth of experiment?

Did they try curved crocks, single crocks, multiple pieces, flat pieces?
type of crock? Age of crock?

You can design an experiment to disprove anything as long as you're defining the anything.

[marchogaeth]

I wouldn't say it is a one-off experiment, its been known for 100 years or more than water doesn't move well between different substrate types. Folk still have difficulty with getting their head around it ... me included!

Personally, the question I want answered is "Once the water HAS moved to the crocks surely it then flows freely out of the one hole at the bottom of the pot" - so perhaps the soil-to-crocks flow rate is better than the soil-to-drainage-hole rate?

Given that "crocks are bad" for drainage (assuming we just go with the science ) I think there is a big gain using ALL the pot for compost, rather than wasting 1/3rd (or whatever) of it for extra-drainage

This from Linda Chalker-Scott a Horticulture Professor at Washington State University. I do find she bangs her drum loudly on only one side when she discusses such things, but IMHO she knows the science better than most.

http://puyallup.wsu.edu/~linda%20cha...20drainage.pdf

Just want to echo these comments, really. It is the moving across the "barrier" between two substrates story. You do need to be sure the substrate in the whole container is as free draining as you need it to be for the plants in it.

Also, follow Two Shed's watering advice video which I'm hoping she will pop in and give a link to.

[Potstubsdustbins]

25 years ago I was using crocks, 15 years ago I had moved to polystyrene for the last 5 years I have used nothing.

The compost does not fall out as you would think, but the biggest thing I have noticed is that when I empty a container its full of roots. That says to me the plants are making use of the extra compost.

[BertieFox]

It depends largely on the type of pot you are using and for the old clay or porcelain pots I would certainly go on using crocks, stones, or anything else that aids drainage and protects the drainage hole from blocking up. Most of our problems nowadays are because so many pots are made without drainage holes at all, or with inadequate ones. There seem to be pots now with drainage holes in pillars that stick up into the compost, based on the idea the bottom of the pot will retain some water.... a very bad idea. I just don't believe this Which survey was properly carried out or across a wide enough range of planting mediums and pot types. There are problems with modern composts which easily waterlog and/or dry out and cannot be re-wetted easily, and for many purposes you cannot beat the old John Innes types, almost impossible to find nowadays.

[Chippy Minton]

But the big question is.....

What am I supposed to do now with all my broken bits of pot

I think the article implied that it may have just been a use for broken pot. Maybe I'll put them with all the stones I dig out of the beds and make a path faster

[Richard Eldritch]

I wonder if crocks also help by air pruning the roots, preventing them from winding at the bottom?

[Potstubsdustbins]

I suppose it also depends on what you use your pots/containers for. All my plants are in a pot/container of some sort from beginning to end. My smallest discounting modules is 2 1/2" up to 7" in what most people would call a pot. Moving through Morrison's flower buckets, various sizes of self watering plastic troughs with a base reservoir, large earthenware planters and troughs, 40 & 50 gallon plastic water tanks and of course my dustbins.

As to containers that have a water reservoir being bad for your plants I have never found this to be a problem. To the extent I was so pleased with the performance of the purpose made troughs with a water reservoir I now line my hanging baskets with plastic sheet and only pierce it for drainage in the top two thirds leaving the bottom third to hold water.