The most common and most likely answer to this crossword clue is the 10 letter word GREENHOUSE
I've seen this crossword clue in The Daily Telegraph
G
R
E
E
N
H
O
U
S
E
More clues leading to the result GREENHOUSE
- Immature group of pupils in cockpit
- Unqualified legislative body that covers up bloomers
- G Eco-friendly domestic cockpit
- Eco-friendly place used for cultivation
- Common uniform, wearing stockings in see-through construction
- Cutting temperatures toughens tree out in conservatory
- Environmentally friendly residence that’s of growing importance
- Ecofriendly sign, to be building for growth
- Ecofriendly sign somewhere hot
- Sign on new nursery
Buddy explains!

The straight part
We know that "conservatory" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case conservatory = greenhouse.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GREENHOUSE mean?
GREENHOUSE noun- A building used to grow plants, particularly one with large glass windows or plastic sheeting to trap heat from sunlight even in intemperate seasons or climates.
- The glass of a plane's cockpit.
- A structure that shields the operating table to protect against bacteria.
- A hot state in global climate.
- To place (plants) in a greenhouse.
- To nurture in order to promote growth.