Pokojovou rostlinu chci přesadit do nového květináče.

Because it is the direct object of the verb přesadit: it is the thing being repotted.

In Czech, a feminine noun like rostlina changes in the accusative singular:

• pokojová rostlina = a houseplant (dictionary/basic form, nominative)
• pokojovou rostlinu = a houseplant (as a direct object, accusative)

Both the adjective and the noun change:

• pokojová → pokojovou
• rostlina → rostlinu

So Pokojovou rostlinu chci přesadit... literally has the structure [houseplant-ACC] I want to repot...

Because the preposition do requires the genitive case when it means into or to the inside of something.

So:

• nový květináč = a new flowerpot (nominative)
• do nového květináče = into a new flowerpot (genitive after do)

Both words change:

• nový → nového
• květináč → květináče

This is a very common Czech pattern:

• do domu = into the house
• do školy = to school
• do nového květináče = into a new flowerpot

Přesadit means to transplant or to repot, depending on context.

With a plant, it usually means moving it from one pot or place to another. In this sentence, since we have do nového květináče, the natural English meaning is to repot.

Related forms:

• sadit = to plant
• zasadit = to plant / put in
• přesadit = to transplant, replant, repot

The prefix pře- often adds the idea of moving or doing again in another place.

Because it follows chci, which means I want.

The pattern is:

• chtít + infinitive = to want to do something

So:

• chci spát = I want to sleep
• chci jít = I want to go
• chci přesadit = I want to repot

This works much like English want to + verb.

This is about aspect, which is very important in Czech.

• přesadit = perfective: the action is seen as a complete, finished event
• přesazovat = imperfective: the action is seen as ongoing, repeated, or habitual

In this sentence, chci přesadit suggests I want to repot it as one complete task.

Compare:

• Chci přesadit pokojovou rostlinu. = I want to repot the houseplant.
• Chci přesazovat pokojové rostliny častěji. = I want to repot houseplants more often. / I want to be repotting houseplants more often.

So přesadit is the natural choice for a single completed action.

Yes, it is normal. Czech word order is much more flexible than English word order because case endings show the grammatical roles.

A more neutral order might be:

• Chci přesadit pokojovou rostlinu do nového květináče.

But starting with Pokojovou rostlinu gives it a little more emphasis or makes it the topic of the sentence.

So these are all possible, with slightly different focus:

• Chci přesadit pokojovou rostlinu do nového květináče.
  Neutral: I want to repot a houseplant into a new pot.

• Pokojovou rostlinu chci přesadit do nového květináče.
  Focus on the houseplant.

Czech speakers often move words around for emphasis, rhythm, or context.

Yes. That is also grammatical and natural.

All of these are possible:

• Chci pokojovou rostlinu přesadit do nového květináče.
• Chci přesadit pokojovou rostlinu do nového květináče.
• Pokojovou rostlinu chci přesadit do nového květináče.

The difference is mainly focus and style, not basic meaning.

For a learner, Chci přesadit pokojovou rostlinu do nového květináče is probably the easiest neutral version to produce.

Pokojová rostlina means houseplant or indoor plant.

It is made up of:

• pokojový / pokojová / pokojové = room, indoor, relating to a room
• rostlina = plant

So literally it is something like a room plant, but natural English is houseplant or indoor plant.

Yes, květináč means flowerpot or plant pot.

Even though the word contains květ / flower, it is also used for pots containing ordinary plants, not only flowering ones.

So in this sentence, do nového květináče is naturally:

• into a new flowerpot
• or more idiomatically in English, into a new pot

Usually chci is enough.

In Czech, the verb ending already shows the person:

• chci = I want

So the subject pronoun já is often omitted unless you want extra emphasis or contrast.

Compare:

• Chci přesadit pokojovou rostlinu. = I want to repot the houseplant.
• Já chci přesadit pokojovou rostlinu. = I want to repot the houseplant. (maybe not someone else)

So in most situations, leaving out já is perfectly normal.

The adjectives must agree with the nouns they describe in gender, number, and case.

Here you have two adjective + noun pairs:

1. pokojovou rostlinu

   • noun: rostlina
   • gender: feminine
   • number: singular
   • case: accusative
   • adjective must match: pokojovou

2. nového květináče

   • noun: květináč
   • gender: masculine inanimate
   • number: singular
   • case: genitive
   • adjective must match: nového

This agreement is one of the key systems in Czech grammar.

Because masculine nouns change form according to case.

The basic form is:

• květináč = flowerpot

After do, you need the genitive singular, which is:

• květináče

This is a normal masculine pattern. Many masculine inanimate nouns form the genitive singular with -e or -u, depending on the noun type.

So here:

• ten květináč = the flowerpot
• do květináče = into the flowerpot

A rough pronunciation guide is:

• Pokojovou ≈ po-ko-yo-vou
• rostlinu ≈ rost-li-nu
• chci ≈ kh-tsi
• přesadit ≈ pshe-sa-dit
• do = do
• nového ≈ no-vay-ho
• květináče ≈ kvye-ti-naa-che

A few useful notes:

• ch in chci is like the ch in German Bach or Scottish loch
• ř in přesadit is the famous Czech sound, something like a mix of r and zh
• stress in Czech is usually on the first syllable of each word:
  • POkojovou
  • ROStlinu
  • CHCI
  • PŘEsadit
  • DO
  • NOvého
  • KVĚtináče

Yes. Czech does not have articles like a and the, so the sentence by itself does not explicitly mark that difference.

So pokojovou rostlinu could be understood as:

• a houseplant
• the houseplant

Which one is intended depends on context.

For example:

• If you are talking generally, it may feel like a houseplant.
• If both speakers already know which plant you mean, it may feel like the houseplant.

That is very normal in Czech. Context does the work that articles do in English.