Breakdown of Tu disseste que nós faríamos um churrasco no jardim.
tu
you
nós
we
um
a / an / some (all forms)
em
in / on / at
Questions & Answers about Tu disseste que nós faríamos um churrasco no jardim.
Why do we use the conditional faríamos here instead of the future tense faremos?
This is the core rule of backshifting in reported speech. If the original direct quote was 'We will have a barbecue' (Nós faremos um churrasco) using the future tense, and the reporting verb is in the past (disseste), the future tense must shift back to the conditional (faríamos).
The verb is fazer, so why isn't the conditional form fazeríamos?
Fazer is one of a few verbs with an irregular stem in the future and conditional tenses. Instead of using the full infinitive, it uses the shortened stem far-. Then you add the standard conditional ending for nós, which is -íamos, resulting in faríamos. Other common verbs that do this are dizer (dir-) and trazer (trar-).
Would it be wrong to say para o jardim instead of no jardim?
Yes, it would sound strange here. No (a contraction of em + o) indicates the static location where the event is happening (in the garden). Para o jardim implies physical movement towards a destination (to the garden), which doesn't fit the stationary action of holding a barbecue.
Is it necessary to include the subject pronouns tu and in this sentence?