Pokojová rostlina potřebuje nejen zálivku, ale i rozptýlené světlo.

Rostlina means plant.

Pokojová rostlina means houseplant / indoor plant.
The adjective pokojová comes from pokoj (room), so it literally means something like room plant.

• rostlina = plant
• pokojová rostlina = houseplant

So the adjective adds the idea that this is a plant kept indoors.

Pokojová is an adjective agreeing with rostlina.

Since rostlina is:

• feminine
• singular
• nominative (the subject of the sentence)

the adjective must match it:

• pokojový = basic dictionary form (masculine)
• pokojová = feminine singular nominative
• pokojové = could be other forms, depending on gender/case/number

So pokojová rostlina is a standard adjective + noun agreement pattern.

Potřebuje means needs.

Its infinitive is potřebovat = to need.

This is the:

• 3rd person singular
• present tense

So:

• já potřebuji / potřebuju = I need
• ty potřebuješ = you need
• on / ona / ono potřebuje = he / she / it needs

Here the subject is pokojová rostlina, which is singular, so potřebuje is the correct form.

Because zálivku is in the accusative case.

The verb potřebovat usually takes a direct object in the accusative, just like English need takes an object:

• plant needs what? → watering
• zálivka = nominative form
• zálivku = accusative singular

Since zálivka is a feminine noun, its accusative singular changes from -a to -u:

• ta zálivka = the watering
• vidím zálivku = I see the watering
• potřebuje zálivku = it needs watering

Here zálivka means watering or watering supply, not just water in the abstract.

So the sentence is not simply saying the plant needs water as a substance, but that it needs proper watering.

That is why zálivka is a natural word here:

• voda = water
• zálivka = watering

In context, potřebuje zálivku is very natural for plants.

Actually, světlo is also in the accusative, but for this noun the accusative looks the same as the nominative.

Světlo is:

• neuter
• singular

For many neuter nouns, nominative singular and accusative singular are identical:

• to světlo = the light
• má světlo = it has light
• potřebuje světlo = it needs light

So the case did change in function, but not in visible form.

Rozptýlené is an adjective meaning diffused, scattered, or in plant-care language usually indirect / diffused light.

It agrees with světlo, which is:

• neuter
• singular
• here accusative (same form as nominative)

So the adjective must also be neuter singular accusative, which here looks like -é:

• rozptýlený = masculine
• rozptýlená = feminine
• rozptýlené = neuter

So:

• rozptýlené světlo = diffused/indirect light

This is a very common Czech structure meaning:

not only ..., but also ...

In the sentence:

nejen zálivku, ale i rozptýlené světlo
= not only watering, but also diffused light

You can think of it as a fixed pairing:

• nejen = not only
• ale i = but also

Czech also sometimes uses:

• nejen ..., ale také ...
• nejen ..., ale i ...

Both are common.

I here means also / too / even, depending on context.

In ale i, it strengthens the second part:

• ale i rozptýlené světlo = but also diffused light

You may also see:

• ale také
• sometimes just ale

But nejen ..., ale i ... is a very standard and natural combination.

So yes, i is important here because it gives the full not only X, but also Y meaning.

Czech has no articles.

English says:

• a houseplant
• the houseplant

Czech simply says:

• pokojová rostlina

Whether it means a or the depends on context.

So this sentence could translate as:

• A houseplant needs not only watering, but also diffused light or
• The houseplant needs not only watering, but also diffused light

The Czech sentence itself does not mark that distinction.

The sentence is natural as written, but Czech word order is generally more flexible than English.

Standard version:

• Pokojová rostlina potřebuje nejen zálivku, ale i rozptýlené světlo.

This sounds neutral and clear.

The important thing is keeping the paired structure nejen ... ale i ... together in a sensible way. Czech can move elements around for emphasis, but for a learner this word order is the safest and most natural.

A rough pronunciation guide:

Pokojová rostlina potřebuje nejen zálivku, ale i rozptýlené světlo.

Approximate English-style guide:

PO-ko-yo-vaa ROST-li-na po-TRZHE-bu-ye NE-yeN ZAA-leef-ku, BA-lee rosp-TII-leh-neh SVYET-lo

A few helpful notes:

• Czech stress is usually on the first syllable of each word.
• ř in potřebuje is difficult; it is a special Czech sound, something between r and zh.
• ž sounds like the s in measure.
• ě often softens the previous consonant.
• světlo is pronounced roughly svyet-lo.

You do not need perfect pronunciation immediately; the key is first-syllable stress and clear vowels.

Yes, if the subject is already clear from context.

Czech often drops the explicit subject when it can be understood, but here the noun pokojová rostlina is not a pronoun, so removing it changes the sentence from a full general statement to something more context-dependent:

• Pokojová rostlina potřebuje... = a full statement about a houseplant
• Potřebuje... = It needs... / She/he needs..., depending on context

So grammatically it is fine, but it would no longer explicitly say houseplant.

Grammatically, it is singular: pokojová rostlina = a/the houseplant.

But in Czech, as in English, a singular noun can express a general truth:

• Pokojová rostlina potřebuje...
  = A houseplant needs...

So even though the form is singular, the meaning is general and instructional, not necessarily about one specific plant.

The biggest things to notice are:

1. Adjective agreement

   • pokojová rostlina
   • rozptýlené světlo

2. Accusative after potřebovat

   • potřebuje zálivku
   • potřebuje světlo

3. The fixed contrast pattern:

   • nejen ..., ale i ... = not only ..., but also ...

4. No articles in Czech

   • pokojová rostlina can mean a houseplant or the houseplant

5. General statement in singular

   • singular form, but general meaning

So this one sentence is a good example of vocabulary, case, adjective agreement, and a common linking structure all at once.