Container Gardening, Now With Less Deck Collapse!
April 21, 2016 1:24 PM   Subscribe

When installing a container garden, does the distribution of weight matter for the safety of the deck it's sitting on?

The Chicago winter is finally (mostly) gone (I think), and it's time to start putting out a container garden on the deck of my new place. The deck is on the second floor, so I am going with self-watering containers to limit dripping onto my neighbor's deck below. The deck is quite large-- about 100 square feet-- so I have lots of room for containers, yay! However, I realize that at 2 cubic feet of soil per container, I'm looking at each container weighing around 200 pounds. In my research I see that I can expect the deck to hold something like 40 pounds per square foot-- however, I'm wondering whether the distribution of that weight matters. In short, would I be OK putting my containers along the railing of the deck, or would it be wiser to arrange them along the edge of the deck that attaches to the building? I figure the only thing my downstairs neighbor would like even more than not having water constantly dripping on her is for the deck to not completely collapse, so... help!
posted by shaka_lulu to Home & Garden (8 answers total) 2 users marked this as a favorite
What kind of building are you in, exactly? What's the building and deck constructed out of? Also, orientation of deck supports.
posted by lizbunny at 1:36 PM on April 21, 2016

Distribution matters. IE: the 40 per square foot is per square foot.

Is the deck cantilevered? If yes then up against the wall would be best. If the edge of the deck is supported from below then it shouldn't much matter though it would be best to have it over the vertical supports from below.
posted by Mitheral at 1:37 PM on April 21, 2016

It depends on the layout of the deck and 5he supports. Luckily (assuming the deck is of equal weight and strength everywhere) it's 100% the same principle as how a lever works. The farther the weight from the supports, the more force from the weight, just like pushing on the end of a lever. If the deck is only attached to the building and sticks out in the air, then the closer to the building, the less force from the planter. If the deck is attached to the building and has columns at the outside corners, then the best places are above those columns and next to the building.
posted by Homeboy Trouble at 2:10 PM on April 21, 2016

Also important is the soil you use. The weights given are generally for wet soil; if you buy soil made specifically for self-watering containers (without wetting agents), the soil should drain faster and hold less water.
posted by snickerdoodle at 2:17 PM on April 21, 2016 [1 favorite]

post pictures of your deck from above and below
posted by Jacqueline at 5:23 PM on April 21, 2016

People are right that it depends on how the deck is built. If you want to know the best spots for your pots on your specific deck then I'd need to be able to walk around it. Even photos might help in a limited way, if they can give a general sense of the construction style and overall condition of your deck.

Assuming that your deck is a fairly standard U.S. suburban-style deck with wooden posts that anchor into appropriate concrete footings and a ledger board that is correctly lagged into a major structural member of the house, and assuming that the framing is sufficient, and assuming that the deck is in good general condition and was made sometime in the last, oh, 20 years by someone who knew what they were doing and was trying, you should be good to put your pots most anywhere.

However. If I were at all concerned about the deck's ability to support the weight of the pots, I would try to place them on top of posts, over beams, and near the house as much as possible, and I would definitely distribute them around the deck as much as I could. Those are the strongest parts of a well-made deck. If you have reason to believe that your deck was not built right (for instance, many decks have absent or insufficient footings, and many decks have ledgers that are only nailed on) or that part of it is damaged (for instance by rot) then I would avoid placing my pots near the compromised spots.

In all likelihood you'll be fine whatever you do, but you're right to have some caution. Wet dirt is heavy, and decks are often poorly made or in poor condition. Bad decks are certainly known to collapse from time to time, and overloading one is the easiest way to do that.
posted by Anticipation Of A New Lover's Arrival, The at 5:35 PM on April 21, 2016

Oh. I would like to emphasize that the most important thing to do is to spread your containers out as much as you can. If your container weighs 200lbs and has a footprint of two square feet, that's almost a 50% overload even for a deck that's brand new and fully up to current codes. That's likely not a problem if you don't cluster those loads too close together (the empty space around each heavy container should help average things out a bit) but if you put all your pots in the same place and fill them all up you might be in trouble. You'd certainly exceed the rated capacity for that part of the deck; all bets are off after that.

You don't have to go crazy about evenly distributing your containers, but try to break up the groups. I can't tell you what the optimal distribution would be or what the maximum number of containers you can have is; I would have to know a great deal more about the specifics of your situation, and also I would have to be a structural engineer.
posted by Anticipation Of A New Lover's Arrival, The at 5:45 PM on April 21, 2016

You should also consider that the weight of the pots isn't a constant, and that you can lighten them (somewhat).

You can grow plants in pots that are mostly styrofoam pellets. In a horticulture class in college I heard about a a rooftop garden with trees in pots, and the architects and garden designers were uncertain whether the roof could support the weight of the trees and the wet soil. So they planted them in a layer of dirt a few inches deep over a pot full of styrofoam pellets. Apparently the trees were fine, since their feeding roots could find their way into the dirt, and any taproots could still reach water, and in any case as pot plants they would be fed with liquid fertilizer. The styrofoam would hold onto water long enough for the roots to get some of it but not become waterlogged and heavy.

So if you are concerned about weight, I would get some of those lightweight foam pots and some foam pellets for the bottoms of the pots. I would maybe put a brick or something in the bottom of the pots if they are really deep and if you are concerned about them being top-heavy and blowing over.
posted by Lycaste at 7:12 PM on April 21, 2016 [1 favorite]

« Older Catastrophizing about what could be a catastrophe   |   It IS the largest country in the world Newer »
This thread is closed to new comments.