O substrato e o adubo estão no vaso.

Because substrato and adubo are two separate singular nouns, and in Portuguese it is very common to use an article with each one:

• o substrato
• o adubo

Both nouns are masculine singular, so they both take o.

You may sometimes see article omission in other contexts, but for a learner, o substrato e o adubo is the safest and most natural pattern.

Because together they form a compound subject: o substrato e o adubo = two things.

In Portuguese, when two singular nouns are joined by e and act as the subject, the verb normally goes in the plural:

• O substrato está no vaso. = one thing
• O substrato e o adubo estão no vaso. = two things

So estão is the 3rd person plural form of estar.

Portuguese usually uses estar for location:

• está no vaso
• estão no vaso

That is true even when the location is not especially temporary. In Portuguese, physical location is normally expressed with estar, not ser.

So:

• O adubo está no vaso. = correct
• O adubo é no vaso. = not correct for location

No is a contraction of:

• em = in, on, at
• o = the

So:

• em + o = no

That means no vaso literally corresponds to in the pot.

Other similar contractions:

• na = em + a
• nos = em + os
• nas = em + as

Examples:

• na casa = in the house
• nos vasos = in the pots

Because Portuguese normally contracts em + o into no.

So:

• em o vaso = grammatically broken / not the normal form
• no vaso = correct

This kind of contraction is extremely common and something learners need to get used to.

Yes, vaso can mean several related things depending on context.

In a gardening sentence like this, vaso usually means:

• flowerpot
• plant pot
• container for a plant

In other contexts, vaso can also mean:

• vase
• other kinds of vessel/container

So here, because the sentence talks about substrato and adubo, the gardening meaning is the natural one.

They are not the same thing.

• substrato = the growing medium, the material plants grow in
• adubo = fertilizer, something added to nourish the plant

In everyday speech, learners often first encounter terra for soil, but substrato is a bit more specific and technical in gardening. It may include soil, bark, coconut fiber, perlite, and other materials used for cultivation.

So in this sentence, the idea is that both the growing medium and the fertilizer are in the pot.

Yes. Dentro do vaso means inside the pot and is a bit more explicit.

Compare:

• no vaso = in the pot
• dentro do vaso = inside the pot

In many situations, no vaso is the most natural and normal choice. Dentro do vaso adds emphasis to the idea of being physically inside.

Yes. Portuguese allows some flexibility in word order.

The neutral order is:

• O substrato e o adubo estão no vaso.

But you could also say:

• No vaso estão o substrato e o adubo.

That version sounds more marked or descriptive, as if you are focusing first on the location.

For most learners, the original order is the best default.

You learn noun gender partly from exposure and partly from the article that goes with the noun.

Here you can see:

• o substrato
• o adubo

That tells you both are masculine singular nouns.

A useful habit is to learn nouns together with their article:

• o substrato
• o adubo
• o vaso

That makes it much easier to build correct sentences later.

Estão has a nasal ending, which is very common in Portuguese.

A rough pronunciation guide is:

• es-TÃÕ

The final -ão is a nasal sound, not a fully separate a + o like in English. English speakers often need practice with this.

Also notice:

• está = singular
• estão = plural

So the sentence changes like this:

• O substrato está no vaso.
• O substrato e o adubo estão no vaso.

Sometimes Portuguese can omit articles, but in this sentence the version with articles sounds much more natural and standard:

• O substrato e o adubo estão no vaso.

Without articles:

• Substrato e adubo estão no vaso.

That can sound more like a label, a heading, or a very general statement. For normal everyday sentence use, the form with o ... e o ... is the best choice.