I'm confused by 'si vous pouviez ajouter'

Refrain from using conditional in the Si-clause. That's why there is imparfait here. It is, by the way, the same in English:

If I had time, I would come. And NOT "If I would have time, I would come".

Si vous pouviez ajouter -- if you could add. Note that "could" here is actually the imperfect and not the conditional (even though the conditional form is also "could").

 

This can be considered as a 'si clause' without the 'then' or 'result' clause expressed (if you could add cotton flowers, I would/could give them to my wife etc), and the rules for tenses following si hold. The 'si clause' is the clause setting the condition, and the conditional form is not used in that clause:

https://www.lawlessfrench.com/grammar/conditional-mood/

https://www.cliffsnotes.com/study-guides/french/french-ii/french-ii-conditional-mood-and-conditions/conditional-sentences#:~:text=A%20conditional%20sentence%20is%20made,result%2C%20or%20main%2C%20clause.&text=The%20tense%20used%20in%20the,si%20generally%20means%20%E2%80%9Cif.%E2%80%9D

The fact that English translates both French forms - imparfait and conditional - to 'could' certainly adds to the difficulty here!

(Apologies for the ridiculous length of the 2nd link - I don't do 'bitly', and neither does that site apparently)