Support for climbing rose with pressure for second length before summer (4,6)
I believe the answer is:
rope ladder
'support for climbing' is the definition.
(rope ladders are for climbing up or down)
'second length before summer' is the wordplay.
'second' becomes 'rope' (I can't justify this - if you can you should give a lot more credence to this answer).
'length' becomes 'l' (abbreviation in geometry).
'before' says to put letters next to each other.
'summer' becomes 'adder' (someone who adds or does sums).
'rope'+'l'+'adder'='ROPE-LADDER'
'rose with pressure for' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for rope ladder that I've seen before include "Shaky steps" , "not a stiff route to the top" , "Something to get you down" , "etrier" .)