Window box bracket without nails?

Here's one idea where they used a plastic rectangular window box and a tension rod. Maybe this might work for you.

https://homemadebacon.wordpress.com/2011/05/03/urban-herb-gardening

There are support brackets. I searched window box brackets and found a bunch. https://www.wayfair.com/Sun-Joe--Deco-Rectangular-Bracket-FPH1901B-FPH1901W-L7299-K~JOO1085.html?refid=GX330539932276-JOO1085_12639707&device=c&ptid=651319284711&network=g&targetid=aud-354999624471:pla-651319284711&channel=GooglePLA&ireid=13560297&fdid=1817&PiID%5B%5D=12639707&gclid=EAIaIQobChMIldLj66XR6AIVE9tkCh0JpQnoEAQYESABEgJEyPD_BwE

I found one that has clamps:

https://www.bestnest.com/bestnest/RTProduct.asp?SKU=ACD-SFB-02C&src=froogle&kw=ACD-SFB-02C&gclid=CjwKCAjwg6b0BRBMEiwANd1_SBcSpBM7QskC66GsgnHsYpyFtocpkiez6rKRcf1gVJWU5mczUARJVRoCPXkQAvD_BwE

Here's a post that might help - https://homeguides.sfgate.com/attach-flower-boxes-drilling-holes-26046.html

Hello. Here is a link for windowsill brackets I am not sure if this size or appearance will suit your needs.

https://www.amazon.com/dp/B07W82Q2TB/ref=psdc_13350221_t2_B000LDNQ2U

Maybe with a wing nut and tighten it so it holds on

Hello LK,

Buy brackets for use on balconies maybe! Best wishes.

Maybe something like this?

https://www.walmart.com/ip/Black-Wall-Mount-Plant-Bracket/38471798?wmlspartner=wlpa&selectedSellerId=101007480&adid=22222222228000000000&wl0=&wl1=g&wl2=m&wl3=42423897272&wl4=aud-430887228898:pla-51320962143&wl5=9007128&wl6=&wl7=&wl8=&wl9=pla&wl10=140256681&wl11=online&wl12=38471798&veh=sem&gclid=CjwKCAjwg6b0BRBMEiwANd1_SC84TeUh0DEfT_i42ql8fHi_Qzn5n67ZaOQWae6fWkha_HhRpizJhRoC5DMQAvD_BwE

Maybe look and see if there are any command strips that would work?

I use these  https://www.wayfair.com/Sun-Joe--Deco-Rectangular-Bracket-FPH1901B-FPH1901W-L7299-K~JOO1085.html?refid=GX330539932276-JOO1085_12639707&device=c&ptid=651319284711&network=g&targetid=aud-354999624431:pla-651319284711&channel=GooglePLA&ireid=13560297&fdid=1817&PiID%5B%5D=12639707&gclid=EAIaIQobChMIituGu4nU6AIVDlYMCh0xPAnCEAQYAiABEgJGLPD_BwE

They do make railing window boxes-- they clamp over railings on a porch. Not sure if they'd work with windows, but worth a try!