La meva filla vol plantar una llavor en un test que és a la finestra.

In standard Catalan, possessives like meu / meva / teu / seva usually take a definite article:

• la meva filla = my daughter
• el meu llibre = my book

So la meva filla is the normal everyday form.

You may sometimes see article-less possessives in more literary, fixed, or special contexts, but for a learner, article + possessive + noun is the safe pattern to remember.

Because it agrees with filla, which is a feminine noun.

The possessive changes form to match the noun it goes with:

• el meu fill = my son
• la meva filla = my daughter

So here:

• filla = feminine singular
• therefore meva = feminine singular too

This is the verb voler (to want) followed by an infinitive:

• vol = wants
• plantar = to plant

So:

• vol plantar = wants to plant

This is a very common Catalan pattern:

• vull menjar = I want to eat
• vol dormir = he/she wants to sleep
• volem marxar = we want to leave

Unlike English, Catalan does not need a separate word like to between want and the second verb.

Because Catalan usually uses an article where English also often uses one in countable singular nouns.

• una llavor = a seed

Since llavor is a singular countable thing, the indefinite article una is natural here.

Also, llavor is feminine, so the article is una, not un.

Yes. In Catalan, test means flowerpot / plant pot.

So:

• un test = a pot

This is a classic false friend for English speakers, because English test means something completely different.

Depending on region, you may also hear other words for plant pot, but test is perfectly normal Catalan.

Here en is used for the place where the seed is being planted:

• plantar una llavor en un test = to plant a seed in a pot

With containers or enclosed spaces, en is often the natural choice.

If you want to be even more explicit, Catalan can also say:

• dins d’un test = inside a pot

But en un test is already normal and idiomatic.

Que is a relative pronoun here. It introduces a clause that describes the noun before it.

In this sentence:

• un test que és a la finestra

means:

• a pot that is at the window

So que is doing the job of English that or which.

It most naturally refers to test (pot), because that is the noun immediately before the relative clause:

• una llavor en un test que és a la finestra

The usual reading is:

• a seed in a pot that is at the window

So the pot is at the window, not the seed separately.

That is also what makes the most sense semantically.

This is a very common learner question, because ser and estar do not work exactly like Spanish or English.

In Catalan, ser can be used for location in a neutral way, especially when simply identifying where something is:

• On és? = Where is it?
• És a la finestra = It is at the window

You may also hear està a la finestra in some contexts, especially if the speaker wants to stress the current physical position or temporary state.

In this sentence, és a la finestra is perfectly normal.

Literally, it means at the window.

But in natural English, if we are talking about a flowerpot, the idea is usually something like:

• by the window
• on the windowsill
• at the window

Catalan a is broader than a single English preposition, so the exact translation depends on context.

Because finestra is feminine:

• la finestra = the window

Catalan contracts a + el into al:

• a + el test → al test

But with feminine la, there is normally no contraction:

• a + la finestra → a la finestra

So:

• al test
• a la finestra

Both verbs are related, but they are not exactly the same.

• plantar = to plant
• sembrar = to sow

With una llavor (a seed), some speakers might also use sembrar, because sowing is especially associated with seeds.

But plantar una llavor is still understandable and natural in many contexts, especially in simple everyday speech or learner materials.

A rough difference is:

• plantar is broader
• sembrar is more specifically to sow seeds

The sentence follows a very typical Catalan order:

• La meva filla = subject
• vol plantar = verb phrase
• una llavor = object
• en un test = prepositional phrase
• que és a la finestra = relative clause describing test

So Catalan is being quite straightforward here. The structure is close to English, which makes this sentence easier to parse once you know the vocabulary.