1: Gardener's concoction left in a lot (5)
2: Swamp creature resting tail on a rocky outcrop (5)
3: Open present yonder (4,5)
4: Unappealing environment for a snooze (3)
5: Nightwear and jersey top added in afterthought (3)
9: Climp up on horse on high ground (5)
10: A chair may be material (5)
11: See, you are a cad. (3)
12: Call for help oddly stops (3)