Okay this is an obvious one. You've probably already thought about it but I have to throw it in, just in case it's slipped your mind.
Purchase online advertising where your green community frequently visits to collect information. Yes, for this particular tip, I'm talking about green blogs. Here are a few, but I encourage you to do some research and ferret out more. There may be one or two or ten that exactly fit your audience profile.
- Treehugger has a bevy of green followers that happen to come in many different shades of green, from a light minty green to deep dark forest green and everything in between. Their interest lies in everything from serious political issues to buyer's guides. What I love about Treehugger is their small business option for advertising. They work hard to make sure the little guy has the same opportunities as the big fortune 500.
- IdealBite has a following of the more upscale, less politically motivated, luxury green shopper.
- GreatGreenGoods is a shopping blog. While the traffic isn't as staggering as Treehugger or WorldChanging (see the last bulleted item), if you have a unique eco friendly product, this might be the perfect place for your ad. Just a note, while I love the traffic stats of the whopping sites/blogs like Treehugger and WorldChanging, there's something important to be said for less traffic that is highly targeted. I like the shopping blogs (probably because I am completely in love with the whole social shopping scene) because the visitors are ACTIVELY in a phase of the shopping cycle which makes them a bit more targeted from a web traffic standpoint and more likely to purchase.
- TheGreenGuide is published by National Geographic. Their audience is actively looking for healthy alternatives and educational resources for their homes and families.
- WorldChanging has a large following of tech savvy, highly educated, deeply committed to the environment consumers.
Yep, that's the Green Tip #6 for today. Get out there and bother those bloggers. They secretly love it! 
[...] Green Marketing Tip #6 - Purchase Ads On Green Blogs [...]