what about some sort of bracket that would hang over the entire window sill?

Think window air conditioner. How does it stay in the window without falling? Better yet, why not take an old window air conditioner and convert it into a flower box

But a window air conditioner stays in the window mostly because the window stays closed. For a window box, I'd imagine you'd want to be able to open the window to water and whatnot, or just to enjoy the flowers.

Wish I had a solution! We're in the same boat.

What if the flower box had arms that extended and were mounted from the inside?

Please do not open old electronics that contain coolants. It's in general a poor idea and will expose you to things you do not want to be exposed to.

maybe a "saddle" or panniers inspired? you would have flower boxes from inside and outside?

Is there much of a lip outside the window? You can get clamp on window box brackets. But even if you can find a no drill solution make sure they're ok with you using them anyway. They might have other reasons for not allowing window boxes, like the possibility of them falling and being a liability issue.

@Lorint, that was the gist of my air conditioner point. Every apartment building in New York allows window air conditioners but you'll also see a lot of building bylaws about not hanging anything else off your window/window sill.

I wasn't suggesting to anyone to drink the coolant @VAPID TOAST (great name by the way), just use the frame that supports the air conditioner. Better to recycle these toxic boxes than to throw them into a landfill.

The typical window air conditioner box has a screen on the interior - put a hinged door or window here. It has a screen on the outside - put a window here. The top is usually solid - cut an opening it a few inches from the outside corners. Voila!

Or you could build the same thing from scratch if you are sensitive about toxic waste. ;)

Totally agree with Vapidtoast about not messing around with old coolants and things and I think the "saddle" idea by Pixelspersecond is brilliant.

I was thinking that you could use angled brackets below the window and have the top hit just under the opening. Then you could build a 3 sided box that sticks out the window. Depending on the bracket, you could build as large or small a box (maybe even with a little shelf on the inside) as you wanted.

Post and let us know how/if you solve this problem.

Well, first I'd Google the idea (window boxes) and see if anything suitable is available commercially.

After that, I had a strange idea. Maybe you could hang pots of plants in some kind of mesh bags that would be hooked to the wall inside and only minimally block the window from closing all the way? (something like onion sacks or other kinds of netting...) Each plant would have it's own bag, and you could get ornamental with how you hang them...

Just an idea...

I got an adjustable bracket window box at Home Depot. It only cost about $25.

How about using something similar to an expandable shower curtain rod. You can expand it and secure it to the sides of the outside window opening and somehow attach the flower box to it so that it stays secure. It may be unsightly from the inside (I imagine) but hardly noticeable from the outside.

Perhaps if you built a greenhouse box that fit in the window like an air conditioner but taller? It could have opening panels on the back and front so you could still access the plants or have air flow by opening both panels. Leave a lip along the bottom so things won't fall out. You could add supporting legs inside to avoid any holes in walls. You should probably make the outside part sloped for drainage. It might be possible to adapt some kind of aquarium. If you want the plants to be open air on the outside you could build the box with openable panels on the inside and an open section facing outwards. Should be possible to set up a drainage/automatic watering system too.

Have you seen this? http://blog.makezine.com/2012/06/06/tilt-out-window-garden/ It relies on tension bars, I don't think there's any drilling.

A number of years ago (10?) in Brooklyn there was a fire in an ancient industrial loft building and there was no fire escape. The building was zoned for commercial, not residential use, but people were living in the space anyway. The result was horrible. After that, building inspectors were sent in full force all over every borough to look for code violations, like planters on fire escapes and outdoor window boxes that weren't supported by brackets drilled into the brick or the window sill. If they found these beautiful violations, the landlord was fined.

So I had to bring my window boxes in!!! No more flowers for me except for African violets on the inside window sill!!! And a moth orchid, which actually bloomed again this year!!!

I had attached my dark green plastic window boxes to the outside sill by wrapping sturdy sisal around the lip of the window box, and then making a halter for it, wrapping the twine over and under the box in several places, tying those lines to the sisal wrapped around the lip of the box, then pulling the over and under lines across the window sill and tying them to the radiator grill. Of course, I put these outside only when the heat wasn't on, and took them in just before the heat came back on (usually late October). And I couldn't totally close the windows when the window boxes were in place.

Problems with outdoor window boxes: if you put them out in late Spring, birds, especially starlings and pigeons, love to take a few (like all of them) leaves and twigs for building their nest! Especially lemon thyme! Miniature roses are magnets for aphids, a birdie treat!

Solutions: A chicken wire cage placed around the window box keeps the birds out, but it's unlovely until the plants have filled out. Birds will stay away from petunias because petunias have sticky stems. (I happen to like petunias -- big, colorful blooms -- I consider them the 70's bridesmaid dresses of flowers!) Birds won't take mint (I don't know why), but once the mint is full, they love to roost on the nice soft, cool mint, especially on the hottest days, so then you have to cut back the mint stems they broke.

One year after I'd cleared out the plants but before I took in the window boxes, a pigeon couple built their nest in the window box. Pigeons build conceptual nests: they place any twig-like thing they can find, such as bits of plastic straw or wire, spokes pointing outward, in a ring around the nest area. Just a few, so that you get the idea that this is a nest! The chicks don't go outside this area until they're old enough to start flying -- I think because other than eating, their favorite activity is snuggling, and they are too roly poly top-heavy to move. The chicks have very long straw-like beaks which they insert into the parent's mouth to suck the pigeon milk from the parent (similar to cows milk and human breast milk). Pigeon parents are a great example for us humans -- they work as a team, and they share in taking care of the chicks, even in feeding the chicks! They take turns either sitting on the nest or roosting lookout!

Have you check out the Lee Valley Brick Clips? They don't require any drilling and support a lot of weight, they also stay hidden behind your window box.

An air conditioner support would provide a good base.

http://www.homedepot.com/buy/appliances/air-conditioners-fans-dehumidifiers/ac-safe/universal-light-duty-air-conditioner-support-22962.html

As for using a discarded air conditioner, I personally think that's a great idea - it would make it sort of a "secret" garden box. Most air conditioners (especially the larger ones) have a removable metal sleeve around the electronics/cooling portion of the unit. Take that sleeve off (usually by removing the face plate and taking out a few screws) and you have yourself a completely empty metal box to play with.

Would love more answers to this question! I am struggling too.

You could also use one of the window-mounted cat cages people put out- I think they stay in simply by closing the window around the lip.
http://www.amazon.com/PetSafe-PPA00-10774-Cat-Veranda/dp/B000LRH6CM

the window ac idea sounds good.
out here most ac's are enclosed in a grill, and that works as a flower bed of sorts, specially if you're not using an ac.
there was an AT post sometime back about a deck of trays that could be attached inside the house, saw that?

how about a double box? you can then plant on both sides of the window, the weight of the box on the inside will prevent the box on the outside from falling, and you'd still be able to water and close the window. and you'd get twice the enjoyment...now if only i could think of a way of making that...

@ROBYNDOUBLEU - thanks for the mention of those brick clips - that solves an entirely different problem I'm having at my property!

I had something similar when I lived in NYC, and I'd say definitely run any ideas by your landlady, there aren't just liability issues at stake but also water damage that can occur to the mortar that may be a concern to her.

The only other idea I have, beyond what's mentioned here, is to buy a tool (<$5) at a hardware store that's used to profile interior moldings. Then take the measures of your windowsill inside & outside (you press the tool, which has multiple pins, against the shape and it conforms to it), trace each shape onto paper, until you have a full profile of your windowsills - take that to a metal shop - and ask them to custom-bend brackets to suit your needs. My guess is it would cost somewhere in the neighborhood of $25 per bracket to have something made for your purpose because the material itself for the bracket is cheap stock.

This would work, though your landlord would have to be ok with it.

Put a very heavy window box outside, the length of the window width. Use wood shims to make it level (those window sills slope outward often,) Attach some straps or very strong line that doesn't stretch at all to the back of the window box. Run these inside the window, and either attach by screwing them inside somewhere, if you can put a few screws in inside where they will be inconspicuous and easily filled when you leave, and attach that window box securely. You could also weight these straps or lines by tying to some very heavy weights you find somewhere, sitting on the floor inside the window...and don't ever move them!

I'd just do the plants inside though. Get a wood shelf cut to lay in front of the window in the wells on the sides there that were for the original shutters, and get rid of the plantstand. It will look nicer. And you won't have to worry about the birds and bugs and wind getting your plants. Depending on your light, the outside light in Brooklyn can be too strong all day in the summer for many plants, and the heat can also affect them more out there.

Wow! Less than a year later, on the site all the time and I missed my own question?! Darn! Now let me read what everyone has to say :-)

@renovationconfusion that is amazing!

@SherryBinNH I was thinking about that, the Wally wall pockets just seemed too expensive, but West Elm seems to carry something similar now.

@weatherman this is a great idea, have to measure and see if it would work since there is a ledge but if the window box can be secured to it then maybe!

@talby that is genius and gives me some ideas!

To all who mentioned building something, I truly wish I had the time, patience and/or space for a project like that (or any project for that matter lol!) but maybe if someone wants to help me build some prototypes, we could start a kickstarter fund!

I'll keep ya'll posted :-)