Self watering salad-tray thingy...

[w33blegurl]

Morning! So, I have been wanting to put a raised salad bed outside our back door (think vegtrug type trough on legs - has to be on legs as will be on wooden decking). But as I got to thinking about this (which lets face it is dangerous really...) I wondered if I could make it self watering. So...my plan is to use a plastic trough on legs (can buy this no need to cobble together with my appalling DIY skills), seal the drainage holes in the bottom. Add a layer of gravel as the reservoir with a bit of pipe running vertically from the top of the trough into the gravel to allow me to top up the water in the reservoir. On top of the gravel some kind of mesh - and this is where I could really use your input - and then the compost on top of that.

Where I'm getting a bit stuck is what I should use between the gravel and the soil. I'm thinking either a fine metal (or plastic) mesh or some capillary matting (which I already have a load of in the shed anyway!). Only downside to the capillary matting would be that the roots may well grow through it and its a b*gger to get them out and clean it up when I need to grow the next lot. Also as I'm typing this, I realise I've got a big sheet of polycarbonate I could use as well (would just need to make some holes in it obvs) that used to be the lid of a long-dead cold-frame. Should say this is really aimed at lettuce type crops but may get the odd tumbling tom or similar in there too!

OK...so...I hope that made sense, but if someone has tried this before some pointers would be great! I've had a look on the interwebs but mainly found lots of videos on how to make them using buckets inside buckets which isn't really what I'm after!
Ta muchly!

[Mitzi]

The main problem I can see is how will you know when the water needs topping up and how will you know when to stop? There's a danger that the soil could get waterlogged without drainage holes.

I have some Stewart Balconniere pots which work on exactly the basis you describe but without the gravel. They have an overflow pipe to prevent waterlogging. Gravel will seriously reduce the water capacity so if you need it to support the mesh I'd go for pebbles instead.

[w33blegurl]

Thanks - yes an overflow hole would be needed, had forgotten about that! Precisely why I need some extra brains on this!

[Miss Mousetrousers]

Your trough idea sounds fine except for one thing. If you seal up the drainage holes the soil will get far too wet so there'll be no oxygen for the plants to take up and it'll encourage moulds etc. Put your trough on some sort of base that's got a few holes in the bottom and just a bit larger than the trough, line it with capillary matting, fill the tray to the top with gravel or perlite then set your trough on top. This means that excess water can escape, the matting will have enough water to keep things growing, the gravel will help to prevent it drying out and will also provide a medium for the plants to take root.