We were reading across Martha Stewart's list of projects that can be tackled in a single day (there might be more hours in her day than ours though...) and found one that fit our needs (aka, sills that are too shallow to hold most pots) perfectly! Click through the jump for the how-to, and links to our own, one day diy ideas!
Wanna expand your shelves? Here's Martha's take on on completing the task with ease.
1. Select plywood the same thickness as sill; cut it as wide as sill and 12 inches deep.
2. Attach bottom of shelf to bottom of sill with 3 hinges: 1 at the center, the others near the sides.
3. Cut 2 right triangles from wood thin enough to lie flat beneath folded shelf; trim tips. Brackets should extend 3/4 of the way across shelf and 3/4 down apron.
4. Hinge brackets to apron. Paint before installing.
Not the project you were looking for? Try one of these on for size!
(Photos courtesy of MSLO)

White Enamel Flatwa...
this could make a really nice collapsible desk/eating counter in a tight space as well, with maybe an extra bracket or two to take more weight/traffic.
Really cool idea.
I would rethink this if you had cats, I had a very bad experience involving one of these and a paw, it could of led to amputation.
Beware!
I'm now sitting here trying to imagine HOW this could be dangerous to cats... but I'm stumped. Care to elaborate, Ana?
Please people!
Its "could have" not "could of"
You're mistaking the sound of the contraction "could've"
great notion
Still stuck in the clay pot age. There are better ways.
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i like this idea, but I can see a cat's paw getting accidently stuck in the folding area when they're on the original sill and you're folding the shelf up. Or a fatty catty collapsing the shelf. I've stepped on my cat's little paws so often that I'm afraid she'll lose a paw one day. :(
Hey Greenscaper, cool ideas.
I love this idea. This is the kind of stuff I like to see on this site. Even though it's called apartment therapy, about a third of the content on this site seems aimed at folks that have all the space they need and gardens.