Learn Hardcore Portuguese (Brazil): Se o pepino estiver fresco, eu também vou comprar repolho para a salada. - If the cucumber is fresh, I am also going to buy cabbage for the salad.

Breakdown of Se o pepino estiver fresco, eu também vou comprar repolho para a salada.

Why is estiver used instead of está?

Because this sentence is talking about a possible future condition.

After se meaning if, Portuguese often uses the future subjunctive when the condition is about the future:

Se o pepino estiver fresco... = If the cucumber is fresh / if the cucumber turns out to be fresh...

Using está would sound wrong in this kind of future-looking sentence.

A useful contrast:

Se o pepino estiver fresco, eu vou comprar repolho.
Future possibility
Se o pepino está fresco, eu compro.
More like a general or repeated situation, and not the best match for this context

What tense or mood is estiver, and what verb does it come from?

Estiver is the future subjunctive form of the verb estar.

So:

This form is very common after words like:

Examples:

English usually does not mark this with a special verb form, which is why it can feel unfamiliar.

Why is the verb estar used with fresco?