SWIM grew in Montana at about 5,000 ft. Not quite as high as you but close. Same situation. I hauled in all of my soil. Because of this you'll want to find a spot that you can use for multiple years in a row or better yet build three sites and rotate which one's you use from year to year, that is what SWIM ended up doing. In picking a location take into consideration where the sun will be during the cooler month of harvest to ensure that your plants will get sun all day long. This will help them deal with cooler temps and help in last minute production. If you can find some running water close by. In SWIM's situation this was not the case and thus had to haul it all in. Though this is hard work it's not that big of a deal as you'll get a method and bang it out. SWIM had to do this about ever other week and weekly during the weeks where the temp was around 90deg+. SWIM's biggest problem was animals. Rabbits and deer. Rabbits will burrow and eat the stems base while deer will eat all of the new shoots. Sprays designed to deal with these animals work well and chicken wire over the soil will stop the rabbits. Good luck.