Lightweight Soil for a Planted Roof

lindasewandsew(So Cal 9)December 15, 2011

Does anyone here have a planted roof? I'd love to see some photos and get any advice possible. Most of the roofs on Google are a lot different than what this will be. It's being built to carry more weight than it will ever have. It will be on top of a potting shed and will be about 12'x7'. It won't be very steep. maybe an inch or two drop per foot. The drop will be in the 7' direction.

I'm looking for a lightweight soil recipe, The depth isn't decided, but am thinking 4 inches or so. It will be planted with sedums and other succulents, and possibly a few annuals thrown in to see how they do. I use soil very close to Al's recipes in containers and it's worked out very well (Thanks again Al!!). I have easy access to bulk perlite, pumice and bark that's just the right size, with just a tiny bit of waste. Even though there are large rock quarries in the area, I haven't found the gravel in bulk, so buy it in bags. Thanks, Linda

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Pro-Mix potting mix is my favorite. It's light too.

    Bookmark   December 17, 2011 at 7:39AM
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ykerzner(9 TX)

So do you want a heavier or lighter mix? A good long-term mix for this application would be a mix of pumice and gravel, with no more than 5-10% bark. Perhaps 10-15% sand.

A lighter mix would contain more pumice. On planted roofs longevity is important, so usually the thinking goes that less organic matter is better.

    Bookmark   December 18, 2011 at 3:45PM
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I'm going to plant the roof of my chicken coop when I build it and stumbled across these green paks., I'm taking the idea but making my own with my own mix. I'm going to use bark-turface-pumice, 1-1-1 ratio, I figure this will be light enough, long lasting and still hold enough moisture. This is always open to change up to the day I do it, there is always some new thought that pops into my head as I gather information.


    Bookmark   December 18, 2011 at 9:53PM
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lindasewandsew(So Cal 9)

Thanks for the simple ideas. A lot of the info out there about planting on a roof seems more complicated than it needs to be. Same here with changing the plans often, hoping for a nice outcome when it's all figured out. Linda

    Bookmark   December 19, 2011 at 2:12PM
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greenman28 NorCal 7b/8a

Although I vastly prefer Pumice, I would recommend using Perlite for the low weight.


    Bookmark   December 19, 2011 at 3:14PM
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I just wasn't sure Perlite would hold enough water, and in roof growing your growing your plants in a much shallower container, most systems seem to be only 4 inches deep. I might try a product called Sure Grow Hail, and mix it with my gritty mix, it will take up some space but be much lighter, yes, I think I'll experiment with some mixes this spring.

Josh, I think I read in a post you live in Northern California, and Linda I don't know if your close, but, I went up to the California Academy of Sciences to see their Living Roof, WOW. Check out the web site.


    Bookmark   December 19, 2011 at 7:51PM
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lindasewandsew(So Cal 9)

Thanks for more ideas, I looked up the roof and it's amazing and huge!! I'm east of Los Angeles, but will go see it if we drive up around the area.

I decided to do the roof 4" for a few reasons, weight, amount of soil that has to be mixed, and it seems that the sedums do just fine in shallow soil mix. The depth can still be adjusted, because it's not built yet. Some of the ones on the web are 12" deep, but we won't be growing large shrubs or trees. The soil won't be mixed till the shed is ready, so it doesn't have to sit around in the way.

Perlite would be good. Al said in a former post that perlite changes the dynamic of the soil if you replace something else with it. I don't think it holds much water either. I use it instead of gravel in some pots, due to weight issues, but don't know if it upsets what's needed by the plants. I'm sure that it can be part of the soil mix, but could use an idea of how much should be used.

This roofed potting bench will support plenty of weight when it's finished, even enough for me to climb up there to work on it, but it wouldn't hurt if heavy ingredients were cut back or eliminated. Linda

    Bookmark   December 19, 2011 at 8:49PM
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