If you need some tiny leaves for your bases, now might be the right time to go visit your nearest birch tree and harvest its fruit. I did so myself, encouraged by this great article I chanced upon on Reaper Miniatures website last year: 'Birch Seed Leaves' by Daniel Joyce. The article describes in detail how to prepare your own miniature leaves practically for free.
There are a dozen or so birch trees surrounding my bus station- I've been keeping an eye on them ever since they started blossoming. Yesterday I have determined that they were ripe for picking, so today I stopped on my way home to fill a small bag. Birch tree branches usually hang low, so it is no trouble at all to get to what you need.
After following the instructions from the aforementioned article, including baking it all in the oven for about 15-20 minutes at 120°C and separating the "leaves" from the seeds afterwards, I ended up with this:
I'll probably give some of it away, but even with that this amount should suffice for my basing and terrain needs for the next couple of years...