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View Diary: Growing Vegetables on City Rooftops (42 comments)

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  •  Peat moss? Then what's the nutrient source? (2+ / 0-)
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    Hardhat Democrat, Nulwee

    Peat moss provides no nutrition for the plants and won't hold a heavy plant, like say fruiting bell peppers or eggplants, upright.  Not to mention that it dries out easily necessitating much watering.

    Why not use compost instead?

    I want to live in the future, not in the past.

    by Involuntary Exile on Thu Apr 10, 2008 at 04:13:06 PM PDT

    [ Parent ]

    •  Good question (2+ / 0-)
      Recommended by:
      Hardhat Democrat, wondering if

      A lot of what goes on in these self watering containers is counter intuitive for "normal" gardeners.  There are some pretty sophisticated ideas at play here.  I'm not responsible for any of them, but encourage you to look through the links at the Flickr page for a more detailed explaination.

      There is a one time application of a  slow release granular organic fertilizer that is placed on top of the potting mix (essentially peat moss).  There's enough nutrients in this application to last throughout the growing season.  The whole container is covered with a plastic sheet that keeps the fertilizer from washing away/releasing all at once,  acts as a mulch cover, and prevents evaporation at the same time.  This is part of what lets the official box claim better results with fewer inputs.

      The top 2/3 of the tub are for the growing medium, the bottom third is the water reservoir.  In one corner of the box, a column of potting mix sits down in the water, constantly staying wet.  As the plants up above need water, they draw it through the potting mix.  If you use compost, the water won't wick properly through the soil. If you look here, you'll see the cut-away of the official box.  (We think it's better to make your own though.)

      As long as you keep the reservoir full, and there's an overflow hole that keeps you from over watering, the plant gets enough water.  Last summer, the bigger water using tubs were using 6 gallons every other day.  This year we've worked out a simple automated watering system, so there's no need to manually fill the tubs.

    •  Bruce pretty much covered it (1+ / 0-)
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      CSI Bentonville

      you can have some coarse sand and perlite in with the peatmoss, and make the top layer a bit thicker as well as adding a bit of silt and sand to it.  But you'll still have to stake or trellis heavy plants.

      These are cousins of hydroponics. The idea is to give the roots plenty of water while still keeping them aerated; as well as have nutrients added continuously through the leaching of the fertilizer at the top.  Nutrients that aren't captured on their way down end up in the water, where the plants eventually grab onto them as the water is wicked up into the medium.

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