"We are buying more plants for the garden."
Translation:Compramos más plantas para el jardín.
This is one of those places where a word-for-word translation won't give you the correct result. "Nosotros compramos" or just "compramos" (the "nosotros" is optional) can be translated as either "we buy" or "we are buying". You can't combine a form of ser to mean "are" with another verb. However, you can combine a form of estar with the present participle to form the present progressive tense (or present continuous) tense. For example you could say "Nosotros estamos comprando" or just "estamos comprando" for "we are buying", if you are buying something right now.
For some reason, duolingo is allowing present indicative to mean the same as present progressive.
I don't agree with it and I think it's confusing to new Spanish learners to have two ways of saying something with no explanation given by duolingo as to the difference between them or which one should be used and when.
Present indicative: compramos - we buy
Present progressive: estamos comprando - we are buying
They essentially mean the same thing, there's no difference between:
compramos más plantas para el jardin - we buy more plants for the garden
estamos comprando más plantas para el jardin - we are buying more plants for the garden.
But because duolingo is interchanging them to mean the same thing, they should ALLOW both answers.
Answers using "nosotros compramos" are accepted.
It's not uncommon that people complain about Duo not accepting a different translation for a certain word when the real error is elsewhere in the sentence.
It is always best to share your full answer in the forum so it can be completely checked.
You can always leave out the subject pronoun. And in my experience, Duolingo accepts the sentence both with the pronoun and without it. There is no set reason for when to include or exclude the pronoun because it is optional.
Please note that Jim226018 has reported that answers using "nosotros compramos" are accepted. This would suggest that you had some other issue with your answer.
First, "por" and "para" are not adjectives, don't have gender, and don't change their form.
They both can mean "for", but you use "para" when something is "for the benefit of" or will be received by something or someone. These are plants that will be "received by" the garden and will benefit it. Here is a helpful link: https://www.spanishdict.com/guide/por-vs-para