Agave in shallow, low-weight situation

a22andrewMarch 20, 2013

Hi all,

I'm new here and am hoping I can get some ideas on a challenging situation.

I have a rooftop deck with a load bearing capacity of 200kg per square metre (around 440 pound per 1.2 square yards). I also have a corrugated iron container that is 1.2 meters (1.4 yards) in diamter and about 60cm (2ft) deep, and access to a bunch of semi mature agave.

I can't fill that container with soil or it will go through the roof.

So, any ideas on these challenges?
- How can I fill the container with light weight material (foam??) that will bring the container up to a depth that isn't structurally dangerous?
- How shallow can the soil be for agave? 30cm / 1ft? Technically I shouldn't do 'normal' soil more than 15cm deep.
- Is there a soil alternative that may provide more depth that would be suitable.

... is this a stupid idea?


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What if you built a bench of some sort to fit inside the container, and just keep the agaves potted and sitting on the bench? Or build something like a window box with legs to raise it to the level of the metal container's rim? That way it will be just air space filling up the metal container. My concern would be that whatever you use to fill up the space otherwise (even foam) could hold some water (via capillary action) and make it heavier.

    Bookmark   March 21, 2013 at 12:38AM
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I think that's an excellent idea salt_creep, thanks; I've seen circular plastic planters that would provide a good base (or a pond - just got to find the right size), then I just need some legs or trestles to put it on.

Anybody know minimum depth I should be using for agave? Or a suitable soil alternative?


    Bookmark   March 21, 2013 at 2:17AM
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Tiffany, purpleinopp GardenWeb, Z8b Opp, AL(8B AL)

Having trouble picturing your container in my mind, but worry about toppling from top-heavy-ness and wind. I use fishing line for a lot of plant-related situations and that's what came to mind reading this. If your arrangement will be static, you could make a grid of fishing line at the surface, under the crowns of the plants. Then if a strong gust comes along, the pots and root balls will be stopped from leaving the container by the fishing line. It's unobtrusive and weighs virtually nothing.

If you can find a plastic shelf unit that fits in there, it would probably be more stable than overturned plastic containers. The type where the shelves and supports stack to desired height might work well. Quite strong, inexpensive, and also weigh just ounces. In the winter, you can bring it inside to house tender plants, if that's something you do. You may want to drill a hole or two in the shelves, they usually have a lip for structural integrity.

I don't know how you'd stop the wind from taking them away, but ping pong balls or those plastic balls from those kids' play pits could fill up the empty spaces without weight. Something similar that wasn't spheres would be more stable...

Square plastic milk or laundry soap jugs, if you have those in Aust., could also give you a higher base without weight.

    Bookmark   March 21, 2013 at 9:35AM
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You could pot in a weight-light mix, something with a high percentage of Turface, pumice or perlite. Additionally, the 15 cm sounds deep enough for Agaves in general - mind, they'll likely quickly become root-bound, but So What (excellent Miles Davis tune, btw) - you can remove the pups and cull the herd as need be. Let's see some pictures of your proposal and the great minds here will come out like land sharks to a free meal.

    Bookmark   March 21, 2013 at 10:07AM
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wantonamara Z8 CenTex

Making your soil with perlite and pumice with some compost would keep your soil light. One would have to depend on fertilizer for nutrients. The other thing one could think of is spreading the load outwards from your container by using grids of timbers like skids. It might give things a very structural look that would either look good in a creative architectural way or be loo totally not right in your situation. Just an idea.

    Bookmark   March 21, 2013 at 10:18AM
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Thanks all, some excellent ideas - I will grab a picture tonight and post it up. What I'm thinking at this stage is:

- find a plastic or fibreglass pond that is something like 20cm (8 inches) deep
- drill some holes for drainage
- affix some sort of legs / trestles to raise it to the required height....although filling with light weight plastic junk sounds interesting as an alternative
- put some sort of maerial barrier to hold the soil in / ensure cleanish water only goes through to the deck below
- Fill the pond with perlite / pumice
- plant direct into the pond.... this may add more stabliity than individual pots, I'm thinking.

There are also some good soil alternative ideas here:
which I may have to explore.

What a helpful forum! Glad to find you guys.

    Bookmark   March 21, 2013 at 9:09PM
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smaller tub with 1.3 meter diameter...

    Bookmark   March 22, 2013 at 6:23AM
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Larger tub with 1.5 meter diameter... this one concerns me just because it's so huge. You'll notice that we are quite high up though (deck is effectively the fourth floor), so it will be difficult to get rid of. I'm hoping to find a way of liking it, hence this thread...

    Bookmark   March 22, 2013 at 6:26AM
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If this were mine I might attach a wooden base to make the bottom more rigid when it gets raised up. All that weight might make it sag. Also, I might use wheels instead of legs just in case a dance party pops up on my deck.

Your mix will be pretty light if it's 50-60% perlite. I prefer pumice for growing but it's much heavier. You could also do about 10 inches of perlite on the bottom and 12-14 inches of mixed soil on top.

Don't separate root systems by planting small pots in big pots. You want plants that will take advantage of all that root space and make use of the water you add. It would be better to put too many plants in it and then remove them as they begin to crowd, rather than waiting for a few plants to fill the whole container. Root systems will get tangled as they co-mingle but they keep each other safe by using up the water they're given.

Hopefully, one of our UK members can jump in and give you some local insight. We Americans (and honorary Canadians) have no experience with your weather.

    Bookmark   March 22, 2013 at 11:53AM
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Tiffany, purpleinopp GardenWeb, Z8b Opp, AL(8B AL)

I hadn't realized these were so large, 1.3 meters = over 4 feet. 1.5 = a tad under 5 ft.

I agree with, and this goes along with what Hanz was saying about using a big planter as a mini garden bed, not separately potted plants - Do they have those plastic baby pools around where you are? I wouldn't try legs, which would create too few pressure points, but fill the bottom of the metal container with large pieces of styrofoam, as much as is needed to have the rim of the baby pool slightly under the container. This would spread the load to more, wider points. Just make sure the holes in the baby pool coincide with a crack between pieces of styro or water won't be able to escape.

That should give you about 12" of depth to work with, not too heavy even with bagged potting soil. As mentioned, perlite could increase bulk without weight if needed, and you would want something that harbors little excess water for this type of plant. Baking in full exposure, and winds, should help it dry quickly.

Even a small depth of water is very heavy, so ensuring that water flows through whatever soil mix as fast as it can rain, and on through the pot would be my main concern. Using hot glue to attach screen over a few fairly large holes in the bottom of the container might help. By fairly large I mean several times larger than the largest particles in the soil, so no single particle could possibly block a drain point.

Furniture or appliance stores should be able to give you all the styrofoam pieces you need, gladly.

    Bookmark   March 22, 2013 at 12:40PM
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Oh my, those are some containers - makes me think of the ravine nearby (which uses similar material for drainage). I can see them just chock-full of Agaves and loving it. I second the idea of those on a platform separating them from the deck, and furthermore, would fill the bottom third of them to block off the need for potting medium (upside down pots / plastic buckets / pans do this admirably).

This post was edited by cactusmcharris on Fri, Mar 22, 13 at 15:35

    Bookmark   March 22, 2013 at 1:41PM
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wantonamara Z8 CenTex

The beams to distribute weight would look good with the look that I am seeing One has to fashion a secure rigid bottom. Thje other end of the beams could support a slab of wood for a garden bench, or the other container. A modern minimalist look. Did I mention, I am a furniture builder and designer for my DAY job. LOL.

Yea. I don't usually have to worry about the weight of falling water and snow. Haven't had enough of either to write home about it.

    Bookmark   March 22, 2013 at 8:24PM
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Thanks all. I'm in Australia, not the UK, so certainly no snow. In Melbourne we do have plenty of both extreme heat, near freezing cold, and decent wind at this height. Fishing wire may be required, along with irrigation, etc.

Would styrofoam break down in water over time (just from the constant draining, i mean)? It's an easy solution if not.

Baby pool may be the way to go ... anything light and plastic and the right size I guess. Will take some hunting, but sounds possible.

So, you guys are saying a platform under the iron containers to distribute weight? I'm having trouble picturing this. I am keen to try to integrate these monsters into some sort of integrated, and yes, modern / minimalist, design, so it's an interesting idea.

    Bookmark   March 23, 2013 at 6:02AM
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That's exactly what we're saying - it could be something as simple as a shipping pallet or as expensive as a rosewood frame. A frame would also protect your deck, to a point anyway, from the weight of the pot deforming it.

I have a mate here (from near Brisbane) who says that Melbourne is where I should go when I go to Australia. I also want to see all sorts of venomous creatures and drink your country's wines, not necessarily together.

    Bookmark   March 23, 2013 at 10:49AM
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Tiffany, purpleinopp GardenWeb, Z8b Opp, AL(8B AL)

Nope, styrofoam will not degrade, at least not buried in the ground. If it does, it's a time span of decades, not months or single-digit years.

People use those pot-shaped styro things upside-down where I lived in OH to cover - something, IDK. They were outside all winter, with a brick on top, then stored in garage for summer, last until you accidentally smash it with car or something.

After living here for 5 years, I realized the "mini Caladium" (no such thing, AFAIK) was a Syngonium, a tropical vine, not semi-hardy bulb. Someone had planted it against the house, surrounded with styrofoam blocks. I'm told an elderly lady lived here for about 3 years before I did, so doubt she did that. So after at least 8 years after being buried, styro was intact when I dug it up, just very dirty. Rarely does one get a chance to "play archaeologist." It was kinda fun.

I think you need a serious math nerd to know whether you're adding so much more weight with a platform that it's defeating the purpose. Wood pallets are heavy, but the notion to spread the load is really good.

Some type of sheet metal such as the container, but in flat pieces, would match and might be less weight per sq. inch, IDK. I use these sheets (with much less distinct corrugations) to kill grass and they're pretty easy to drag around. Something aluminum? A piece of the safety-plexi-glass-plastic from a patio table? Usually comes with a nice hole in the middle, no sharp corners, but might need something done to the edge if you'll be bare-footin' up there.

    Bookmark   March 23, 2013 at 12:13PM
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wantonamara Z8 CenTex

One would want to find out which way the floor/ceiling joists under the floor ran and made sure the wood beams Spanned some of the joists to either side of the container to insure the weight would be distributed to other weight bearing structures.I do not think that the added weight of the wood would be much and the added benefit of the weight spread would be good. I would consult an engineer and find out the weight in these containers. I don't know what your floor plan of the the area usage is and if this would work in your situation. I also do not know how much money is available for your project. I would think an engineering STUDENT could answer these questions and would love a little cash to be pressed in their hands. I got an architect to help with my house by a note on a bulletin board at the university.

If one did not like the look of the Void underneath the raised containers, An artisan could grind /cut slots that the beams could slice into keeping the heiht the same as placed on the floor. This would have to be done by a GOOD metal worker with proper tools or one would have a mess of raw jagged ill fitting metal. Then one could use the top of the beams to place the rubber fountain /swimming pool structure. OR, One could add and rivet on a metal fill pieces on the bottom edge to carry the metal cylinder to the floor but this would make the metal cylinders look taller and increase their appearance of vertical mass. Anyway you do this, I would have it drawn out so you know what one is getting into. God, I need to shut my designer mind off.It has a tendency to raise away. I will probably talk you out of it by discussing difficulties and possibilities. It could be a very fun project but it could also be a hair puller if approached wrong.

Styrofoam will not break down but some very knowledgeable professionals on another site said that Styrofoam does leach chemicals that plants don't find beneficial. I forget what chemicals they said or the effects on plants. I am just repeating a remembered conversation.If they are placed on the bottom and one has provided a fast draining soil, that leaching should be going out the container and not ip wards. Roots do find their way into every corner though.

    Bookmark   March 23, 2013 at 2:25PM
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HI all,

To close the loop on this, here is the final product with the smaller planter complete.

What I ended up doing:
- Filling with styrofoam
- Put on pot feet to ensure the deck doesn't get damaged.
- lined the remaining area (above styro level) with pond liner.
- Cut holes in liner for drainage (a lot)
- added plant mesh layer to hold soil in
- Added 5 x 25 litre bags of succulent potting mix
- Added 3 x 20 litre bags of perlite

Total of 150 kg over 1.3 square metres, so within the boundaries. Gave me about 16cm of planting medium to work with.

So far, it's only been a few days, but the Agave seem to be recovering slightly (they did not like being in small pots on the deck - possibly too exposed to wind).

With the larger planter, I'm considering talking to a furniture designer and actually getting it made into a table ... I think it could look ok with a round teak top and 'ribs' at 8 or so intervals between the base and the top... we'll see.

Thanks again for all your help.

    Bookmark   May 16, 2013 at 10:46PM
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I like the look of the container. If you don't mind I have a suggestion: add one more plant or take away one - looks better with odd number of plants.
I would add something trailing (like a trailing/ground cover sedum), or take away one of agaves.

    Bookmark   May 17, 2013 at 12:31AM
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I agree with Rina. A trailing plant would add to your creation, making it look even more phenomenal. Either way... looks great! Love it!

    Bookmark   May 17, 2013 at 1:37AM
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Thanks Rina / Greta - I agree, but I'm nervous about mixing succulents with a different type of plant ... do you agree that I should stick with a succulent ground cover?

    Bookmark   May 17, 2013 at 4:25AM
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oh, I see now that sedum are basically succulent ground covers... now i get it :)

    Bookmark   May 17, 2013 at 5:02AM
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Sorry, I should have mentioned that photos in my previous post are of some ground covers/trailing succulents!
There is many more, I only have few.
Just don't get 'donkey tail' (euphorbia myrsinites) - it is nice, but self-seeds like crazy...Many sedums will hang over sides of the container (sedum spurium is good choice - easy to grow, not invasive, and there is few different colours available. Attached photo showing this sedum growing between the rocks & trailing down - it has red flowers as you can see at very bottom of the photo.).
I also find sedum rupestre Angelina self-seeding too easily, I probably wouldn't get that one for your container either - but it is good grouncover otherwise.


This post was edited by rina_ on Fri, May 17, 13 at 18:57

    Bookmark   May 17, 2013 at 6:53PM
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hoovb zone 9 sunset 23

Some Agaves grow in rock fissures on vertical cliffs--bracteosa for example--they have very little soil in nature. Others expect to develop monster root systems in deep, rich soil.

Which Agaves do you have?

    Bookmark   May 17, 2013 at 8:34PM
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Thanks Rina - very nice example. Might see what I can find tomorrow.

hoovb, agave are all planted, as you can see from the pic up a few posts. Hopefully it will be all good!

    Bookmark   May 18, 2013 at 4:53AM
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