How do you trim it without ending up with brown at the top? We have a raised bed with horsetail already but the only way we have found to avoid the brown layer is to trim each reed individually by cutting just above a joint. We want to plant more in a separate box but it is on the north side of the building (next to bulding). We live in the northern part of San Diego county about 7 miles inland from the coast,. Will it survive?