Raised Bed on a Deck Question

A reader sent me this question asking how I would build a raised bed on a deck.  It's a very interesting question. I've never built a raised bed on a deck before but if I were planning one here's what I would do. But first the question:
Dave,

I want to build a raised bed garden to put on my deck and I need ideas for the design of the bottom. Should it be a solid composite board bottom with small spaces between the boards for drainage? Should the bottom be raised by an 1" or more so I don't have a constant moisture problem with the floor boards of the deck?
would you line the bottom with fabric cloth and then a layer of gravel for drainage? What would prevent the roots from penetrating the bottom and creating an unsightly mess?
Would appreciate your thoughts.

Dale
Comment from Greenland Gardener Raised Beds

Putting a raised bed on a deck is a very cool idea. It puts your vegetables closer to where you want them - right outside your door which obviously will be very convenient. Convenient is an awesome word when applied to a garden since it usually makes for a better maintained garden. My first concern with building a raised bed on a deck would be the deck surface it it sits on. Wood rots (even pressure treated over time) and you want enough space between the bottom of the raised bed and the deck to allow for moisture to evaporate quickly to help reduce or eliminate any rot. I think 3-4 inches might be ideal. Also for convenience you may want to consider attaching caster wheels so that you can move the bed around. With wheels you can follow the sun or move to a new location to allow the deck to dry out underneath.

I like the idea of using the composite boards underneath the bed. Spacing the boards apart with a nail should be sufficient to allow good drainage. If your soil mix is good you shouldn't need the gravel for your bed. In my pots I've been using a 50% compost and 50% mix of peat and fine bark mulch which might work well in a raised bed. The compost will retain the water and provide nutrients while the bark mulch creates drainage. Place the weed control fabric underneath the soil at the base of the bed to prevent the soil from leaking out from the cracks between the base boards.

Another idea for the base is to create a solid interior that will catch water and send the excess to a hose that drains off your deck and maybe into another garden or bucket to save for later use. This would be a lot more work as it would require a drain spout and possibly piping on the interior to collect and direct water to the drain spout.

Build the raised bed as deep as you can so that the roots have plenty of room to grow. Also remember that a raised bed dries out much quicker than an in ground vegetable garden so water accordingly. Since it is elevated it will dry out even faster, just keep that in mind.

Thanks Dale for the question! It's a cool idea and I hope my response helps you out!

Dave                               


Gardeners what do you think? How would you try this project?

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