A planta precisa de umidade.

A is the feminine singular definite article, so a planta means the plant.

• a planta = the plant
• uma planta = a plant / one plant

Portuguese often uses articles a lot, so seeing a here is very normal. In this sentence, a planta most naturally sounds like a specific plant the speaker has in mind.

Yes. Planta is a feminine noun in Portuguese, so it uses feminine words with it:

• a planta
• esta planta
• a planta bonita

The ending -a often suggests a noun is feminine, and planta follows that pattern.

No. Planta can also mean things like a floor plan or layout in other contexts. But in A planta precisa de umidade, it clearly means a living plant.

Context tells you which meaning is intended.

Because the subject is a planta, which is third person singular: it.

The verb precisar in the present tense goes like this:

• eu preciso = I need
• você/ele/ela precisa = you/he/she/it needs
• nós precisamos = we need
• vocês/eles/elas precisam = you/they need

So:

• A planta precisa = The plant needs

Because precisar is very commonly used with de when it means to need.

So the usual pattern is:

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

That is why you get:

• A planta precisa de umidade

In standard Brazilian Portuguese, precisar de is the safest and most natural choice here.

So learners should use:

• A planta precisa de umidade

You may sometimes hear precisar without de in some informal speech, but it is not the best default pattern for a learner. If you want to sound correct and natural, keep de.

Because umidade here is being used as a general, uncountable idea: moisture/humidity.

So:

• de umidade = moisture in general

If you added an article, it would usually sound more specific:

• da umidade = of the moisture / of the humidity

In this sentence, the general meaning is the natural one, so de umidade is the best choice.

Umidade can mean moisture or humidity, depending on context.

In this sentence, it most naturally means moisture, especially the kind a plant needs in its environment or soil.

It is not exactly the same as água:

• água = water
• umidade = moisture / humidity

A plant may need água, but this sentence focuses more on the presence of moisture, not just water as a substance.

A helpful approximation is:

ah PLAN-tah preh-SEE-zah djee oo-mee-DAH-djee

A few notes:

• planta = stress on PLAN
• precisa = stress on SI
• de often sounds like djee in many Brazilian accents before a vowel
• umidade = stress on DA

The final -de in Brazilian Portuguese often sounds like -djee.

You would change both the noun and the verb:

• As plantas precisam de umidade. = The plants need moisture.

Changes:

• a → as
• planta → plantas
• precisa → precisam

The phrase de umidade stays the same.

You put não before the verb:

• A planta não precisa de umidade. = The plant does not need moisture.

This is the normal way to make a sentence negative in Portuguese:

• não + verb

So:

• precisa = needs
• não precisa = does not need