I wanted to offer my experience with growing lemongrass for the benefit of anyone living in a similar climate. Lemongrass is often viewed as a tropical plant, but I've lived at 1800 to 2000 feet for the past 10 years or so and have grown lemongrass outdoors for most of that. In that time I've never lost a plant and I give them no protection in the cold seasons. I've heard other people say they mulch them in the winter, but it hasn't been necessary here. I have some snow most years but it usually melts off within a day or two. There are lows in the 20s every year. The lowest temp I remember is around 20 degrees F, but that was measured well above ground level and I'm sure it was much colder right on the ground. Light frost heaving and shallow freezes are common, but deep freezing of the ground is a rare occurrence. I'm not sure how cold of a climate lemongrass can be grown in, but I'm sure a lot of people who could grow it don't because they think its too cold. If one were to mulch it heavily I'm sure the region could be extended to considerably colder climates than this one. In areas where temperatures dip too low for mulching to be effective, the plants could be potted up and brought in for the winter. I potted mine up and moved them into the greenhouse for one or two years before before my friend told me his plant survived outside near Mariposa.
The plants do freeze back to the roots every year, and they also sprout back very late in the season. It takes some extended hot weather to wake them up and get them going, which is somewhere past June. Since it takes a while to get going in the summer and doesn't grow super fast, there is a limited season for fresh lemongrass from mid/late summer into late fall or early winter depending on the year. Not to worry, to solve that problem I harvest jars of the basal shoots to freeze when it gets cold in the fall. I trim the shoots down to just the more useable parts and stuff the jar full of them. I just used some to make a thai style curry and they were great. When the plants freeze in the winter, I cut the shoots back to stubs and wait for next year.
If you want to grow Lemongrass, plants are sometimes available in nurseries. A possibly easier and cheaper way to get a lemongrass plant though is to buy a shoot of fresh lemongrass and plant it. If the shoot has any roots on it, it will probably grow. Thats how my clump started years ago and has grown on ever since by divisions. Mostly though I don't divide it unless I'm giving starts away. Each year a I toss a little compost on it and otherwise it gets the same treatment as the average other stuff in the garden. I've never seen anything besides me eat it and it doesn't appear to suffer from any disease whatsoever. It is pretty much trouble free.
In cooking I find use for Lemongrass in coconut milk curries, fish and fowl coconut milk soups and marinades among others.