For the most part, palms should be trimmed at least yearly if not more often (resorts trim monthly to keep a perfect looking tree). Most palms look best if trimmed to the horizontal point, or 90 degree point. Never should the palms be trimmed back past the 45 degree point. Always trim the palms back to the point of termination on the trunk below the last spines (if any). Clustering palms such as Phoenix reclinata or Chaemerops humilis can be trimmed to a solitary structure- cutting off all the suckers at the base- or more preferably a clumping structure whereby one would select the best 5 or seven trunks and encourage them while cutting off all the remaining suckers. Many patient years of this clumping structure trimming technique can yield amazing multitrunked trees of very high value.