Combine the strawberries, rhubarb, ginger, agave nectar, water and mint leaves together in a small pot over medium heat. Cut the lime in half, squeeze all the juice out, and add it to the mixture. Throw in the lime too.
Bring just to a boil and lower the heat to a simmer. Simmer for 30 minutes. Cool completely in the pot and strain into a jar. The syrup should be about the same consistency of agave nectar or maple syrup. If it isn't, return the syrup to the pot and simmer another 5 minutes.