Garden of Dust and Thorns — Jeffrey Aaron Miller

The garden on Haven Ridge is the last bastion of green and growing things in a world turned to dust. One day, an army of a thousand men marches out of the desert and lays claim to the garden, capturing the few people who live there. It falls to a young woman named Adhi to find the heart of the garden, where a magic exists that might save it. But these men are servants of Deti Maranam, Lord beneath the Sand, and they bring a dangerous and deadly magic of their own. A brutal fight for survival will determine the fate of the garden and of the whole world.