Toboggan left inside plant (6)
I believe the answer is:
Here is my best explanation:
'toboggan' is the definition.
(I've seen this before)
'left inside plant' is the subsidiary indication.
'left' becomes 'l' (common abbreviation).
'inside' means one lot of letters goes inside another.
'plant' becomes 'sedge' (I can't explain this - if you can you should give a lot more credence to this answer).
'l' going inside 'sedge' is 'sledge'.
(Other definitions for sledge that I've seen before include "Vehicle for travelling over snow", "The vehicle", "Put cricketer off", "Snow vehicle or heavy hammer", "one could go downhill fast", "Narrow cart with runners for travelling on snow", "Make offensive remarks", "Sleigh", "Try rattling opposing players" and "Vehicle mounted on runners".)