A planta precisa de nutrientes.

In this sentence, a is the feminine singular definite article, meaning the.

So a planta literally means the plant.

In Portuguese, you usually need an article before a countable noun like planta when you are talking about:

• a specific plant, or
• a whole class in a general sense

So A planta precisa de nutrientes can mean:

• The plant needs nutrients (a specific plant), or
• Plants need nutrients / A plant needs nutrients (a general statement), depending on context.

Using just planta by itself would sound incomplete here.

Portuguese nouns have grammatical gender, and planta is a feminine noun.

That is why it uses the feminine article a:

• a planta
• not o planta

This is grammatical gender, not biological sex. Even though a plant is not female, the noun planta is still feminine in Portuguese.

A lot of nouns ending in -a are feminine, though not all.

Precisa is the third-person singular present tense form of the verb precisar.

The subject is a planta, which is singular, so the verb must also be singular:

• eu preciso = I need
• você/ele/ela precisa = you/he/she needs
• a planta precisa = the plant needs

If the subject were plural, the verb would change:

• As plantas precisam de nutrientes. = Plants need nutrients.

Because precisar is normally used with the preposition de when it means to need.

So the usual pattern is:

• precisar de algo = to need something
• precisar de ajuda = to need help
• precisar de água = to need water

So:

• A planta precisa de nutrientes.

For learners, the safest rule is:
precisar + de + noun

You may sometimes hear de dropped in informal speech, but standard Portuguese strongly prefers de here.

Here, nutrientes is being used in a general, non-specific way: the plant needs nutrients in general.

So Portuguese uses:

• de nutrientes = nutrients / some nutrients / nutrients in general

If you said dos nutrientes, that would usually sound more specific:

• dos nutrientes = of the nutrients / the nutrients (specific ones already known from context)

Compare:

• A planta precisa de nutrientes. = The plant needs nutrients.
• A planta precisa dos nutrientes que estão naquele fertilizante. = The plant needs the nutrients that are in that fertilizer.

Because plants normally need multiple nutrients, not just one nutrient.

So Portuguese uses the plural:

• nutrientes = nutrients

The singular nutriente is possible grammatically, but it would mean a nutrient or one nutrient, which is not the most natural idea in this sentence.

Yes. Portuguese often uses the singular definite article + singular noun to talk about something in a general way.

So A planta precisa de nutrientes can be understood as:

• The plant needs nutrients (specific plant), or
• Plants need nutrients (general truth)

Context tells you which meaning is intended.

Portuguese can also use the plural for a general statement:

• As plantas precisam de nutrientes. = Plants need nutrients.

Both are possible, but the singular generic structure is very common.

No. Planta can have other meanings in Portuguese, depending on context, such as:

• plant (living organism)
• floor or story of a building
• plan or layout, as in planta do prédio
• sometimes industrial plant

But in A planta precisa de nutrientes, the meaning is clearly the living plant, because nutrients fit that meaning.

A natural Brazilian pronunciation is approximately:

a PLAN-ta pre-SEE-zah djee noo-tree-EN-chees

A few helpful notes:

• planta: the first syllable is stressed → PLAN-ta
• precisa: stress on ci → pre-CI-sa
• de often sounds like djee before a word beginning with n in many Brazilian accents
• nutrientes often sounds roughly like noo-tree-EN-chees

The exact pronunciation varies by region, but that approximation will be understood well.

Yes. Necessitar de is another verb meaning to need.

So this also works:

• A planta necessita de nutrientes.

However, precisar de is usually more common and more everyday in Brazilian Portuguese.

So for most learners, precisar de is the more useful pattern to learn first.