Overgrowth Dual Land Cycle

In a set that revolves around uncontrollable abundant growth, land needs to mean something or there need to be mechanics that interact with land somehow.

My initial instinct was something Zendikarian-like, such as landfall. But I started thinking about it and rewards for playing land don't feel right. The concept of overgrowth means that in actuality, land is becoming less and less available and usable. The sentient races are being shoved off to the side, forced into the mountains and out to the sea. There are "ruins" that are actually only a couple of decades old, overgrown with plants and wildlife (or undead). 

So I thought about how I could incorporate the uncontrollable nature of growth into land use without turning to too much into the direction of actual land destruction, which is problematic design.

This is an allied color set (not tribal, but there are thematic links between allied colors and there will be multicolor spells), and so dual lands are called for. Here's an example of what I'm thinking.

So a dual land you can use immediately. But it's got a life span. It gets overgrown (I probably need to think of a better name then "decay" for the counters) and is no longer usable. And it punishes you when it crumbles, but if you're smart, you can plan for it. This will be the case for each of the dual lands.

Edited to add: I do worry that, design-wise, the penalty doesn't nearly account for the up-front benefits of getting this out on turn one. The countdown may need to be shorter.