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22/02/2014 at 11:35
What do you use to ensure good drainage in window boxes and containers? I've seen lots of recommendations for using packing nuts or broken pots but unfortunately I have access to neither. I read last night that aluminium cans can be used... I have a constant supply of those little metal cases that tea light candles are in... Can I scrunch those a bit and use as a bottom layer? Don't want so poison my plants!!! Also, should I mix some grit with the compost for all containers or just those housing plants that need good drainage? Thanks!
23/02/2014 at 10:54

Hi Logan, i have looked at how aluminium effects plants,i think u need to look yourself as the info says it can effect root growth,however the amounts needed seem to be obscure,i went to (effects of aluminium on plants) to me it looks a no,no,however we know its used on acid soils as a colouration for some plants, id use polystyrene myself broken into bits ,it works perfectly in pots or troughs and is used in packaging everywhere, hope this helps, 

23/02/2014 at 10:56

I've used polystyrene packaging broken into chunks - it works and doesn't weigh the container down too much. 

23/02/2014 at 11:06

Yeah, I'd use polystyrene too in window boxes especially, it's pretty inert. I'm sure you'll find some somewhere. I don't use it anymore because I like to put my used compost on the garden and polystyrene would drive me nuts, so I use only rubble and gravel.

Incidentally, when people talking it aiding drainage, it really only bulks up the soil and takes up space that water but otherwise occupy. Few things actively encourage the water to drain away, for that you'd need pure gravel. You need air pockets large enough to stop capillary action. And drainage holes are sooo easily blocked by the slightest little thing. I had two big pots with just three hose size holes in the bottom filled with 50:50 gravel and compost, it still turned into a bog. They're now filled mainly with gravel with pockets of soil for alpine type plants, and they're raised off the ground more. 

23/02/2014 at 11:09

I save wine corks for using in pots that need good drainage.   They are natural and  lightweight and they also absorb excess mositure which then makes a reserve supply if the compost dries out  too much.   They can be recycled quite a few times too and don't harm the compost heap if they end up in there - unlike polystyrrene chips and so on.

23/02/2014 at 11:13

Wine corks?!  How many??!!  

I was referring to my big terracotta pot with the fig tree in ............ that'd take a lot of corks - and a lot of wine - Obelixx,  I'm seriously impressed!!!!!!!!

23/02/2014 at 12:01

I use polystyrene chunks too but I know what you mean about picking the lumps out when you empty the old compost out Jim 

I've also used small broken plastic pots in the base of big pots to save using loads of compost, but I add some gravel or larger stones to fill the space round them which seems to work quite well. If you cover that with a bit of weed suppressing fabric it stops compost being washed down to block the drainage holes.  

23/02/2014 at 12:46

There u go Dove i knew that Obilexx was on the hooch, buys it by the truck load ill bet 

23/02/2014 at 13:16

No wouldn't use aluminium either. ,polystyrene for me too.  Most shops, stores would have polystyrene packaging to give away I think.  Or local GC as in broken polystyrene trays etc.

23/02/2014 at 17:04

Yeah, I've used cracked up turned plastic pots before just to bulk it out. Sometimes you really don't need all that compost. I've just planted to clematis today, I'd had them in front of my old shed. Because they're clematis I just put some broken terracotta pots to stop the drain holes blocking up and filled with a bag of compost each. I had a good chunk of soil around the base of them though. Don't ask me what varieties they are I lost the labels and didn't make notes. 

23/02/2014 at 17:09

I keep the polystyrene trays that plants come in and break them up and use them. When I have run out of these I use bits of hardcore that I have dug out of my garden  

23/02/2014 at 17:32

...I'm afraid I hate polystyrene with a passion - there was also a segment on GW a little while ago which claimed that you don't need to put anything for drainage at the bottom of pots and containers, just fill with compost.. I think it was Monty Don that said it...   I used to use pea shingle but no longer bother... now I just cover the drainage holes with a roughly 3 inch square piece cut from a plastic pot, each piece with a bit of rim which leaves a small gap.. and cover each hole with a piece...

I usually add extra grit to the compost to aid drainage...

..suppose we've all got our own ways of doing things...

23/02/2014 at 18:43

For me polystyrene adds bulk for temporary plantIngs so less compost is used.  Also good for faster drainage 

23/02/2014 at 18:56


These days we mostly drink Oz or Kiwi wine with screw caps so it's just as well corks can be re-used.  The bottles can come in handy too.........

23/02/2014 at 19:00

Think it also depends what's in the pot - as Jim says. If it's something that's going to live there for a while I'd probably treat it differently to something annual. Size of the pot is a factor too of course.

obelixx - were those bottles all from one session? 

23/02/2014 at 19:03

I too find that polystyrene works well in the base of large containers but if you re pot and use the old compost on the garden, sieving out the polystyrene can be a real pain.

On pots with large drainage holes, I cut Mosquito netting and place at the bottom of the saves the compost falling through and if you catch it right, you can remove it when potting on.

Re the wine corks as drainage/bulk, it is worth remembering that so many "corks" these days are man made rather than natural cork so they won't degrade if you add to your compost bin. 

23/02/2014 at 20:32

In Belgium, Oz and Kiwi bottles are not returnable for a deposit and, until about 10 years ago, there weren't ubiquitous bottle banks so we built up quite a collection of empties.    When English speaking friends learned I intended to build a bottle wall the men all scoffed (closet engineers of the failed variety) but brought me their empties too. 

OH wasn't convinced either but my bottle wall was quick to build and has been in place 10 years and withstood temps ranging from -32C to +38C.   What is not to like?

If you should fancy making one yourselves, the straight sided bottles with high shoulders work best.  No cement needed, just a firm base and an end wall made, in our case, from granite pavers fixed with cement.  The top is made from marble slabs recycled from dismantled fireplaces when we renovated this ex farmhouse. 

23/02/2014 at 23:24

If you want to reduce the amount of compost in the pot, for economy or weight reasons, then adding coarse material in the bottom of pots will work, but what it does not do is improve drainage. Wisley, and many others, have been trying to get rid of this myth for some time. Google "perched water table" and you will see lots of discussions on it. The alpine group at Wisley used to demonstrate to visitors pouring water into identical pots, 1 with crocks and 1 without. The former holds onto more water than the latter, because it sits at the change in growing medium. What it does do is prevent water-logging by takeup from below, which can be useful, and means things like hanging baskets need watering less often, but it actually impedes drainage.

24/02/2014 at 11:55

Thank you tillium2cv! What a relief to hear some common sense. I struggled to get my head around that whole idea from my days at college doing soil science to years later. It just didn't make any sense to me. I did some experiments myself and it was clear that all the extra rocks etc did was take up space that otherwise would have been occupied by water holding compost. I think I've already said as much. And a bucket of gravel or a bucket of clay will still make a pond if you poor water in. By the way, I was watching a recording of GW last night and Monte clearly said adding gravel will improve drainage, despite me shouting at the screen, he  didn't listen!  Let's not forget Monte, as great as he is, and I do have a huge respect for his presenting of GW and his garden, he's not a horticulturalist. Like many GW presenters in the past he's an amateur. That's no criticism; who better to understand the needs of Amateur viewers than an Amateur? Sorry Monte, you've still got my vote. 

24/02/2014 at 11:59
Fairygirl wrote (see)

Think it also depends what's in the pot - as Jim says. If it's something that's going to live there for a while I'd probably treat it differently to something annual. Size of the pot is a factor too of course.

obelixx - were those bottles all from one session? 

Oh, blinking eck, I couldn't see what I was supposed to be looking at, Bottes? What Bottles? Could see the bottles for the wall. 

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