Quan la planta comença a créixer, cada fulla nova sembla més forta.

Quan means when. It introduces a time clause: Quan la planta comença a créixer = When the plant starts to grow.

In this sentence, it sets the scene for what happens next.

After començar (to begin / to start), Catalan normally uses a + infinitive.

So:

començar a créixer = to start growing

This is the usual pattern:

• començar a parlar = to start speaking
• començar a ploure = to start raining

So the a is an important part of the structure.

Comença is the present tense, third-person singular form of començar.

It matches la planta because la planta is singular.

So:

• la planta comença = the plant begins / is beginning

Because cada means each or every, and it normally goes directly before a singular noun without el / la.

So:

• cada fulla = each leaf
• cada dia = each day
• cada planta = each plant

You would not normally say cada la fulla.

In Catalan, descriptive adjectives often come after the noun.

So the most natural order here is:

• fulla nova = new leaf

Putting the adjective before the noun is sometimes possible for style or emphasis, but noun + adjective is the normal pattern in a sentence like this.

Because the subject is cada fulla nova, and cada takes a singular noun and usually a singular verb.

So:

• cada fulla nova sembla... = each new leaf seems...

This is similar to English each leaf seems, not each leaf seem.

Sembla is from semblar, which means to seem or to appear.

So:

• sembla més forta = seems stronger

This suggests an appearance or impression, not an absolute statement. It is a little softer than saying it definitely is stronger.

Because forta agrees with fulla, and fulla is feminine singular.

In Catalan, adjectives usually agree in gender and number with the noun they describe.

So:

• fulla → feminine singular
• forta → feminine singular

Compare:

• un arbre fort = a strong tree
• una fulla forta = a strong leaf

Més means more, and with an adjective it forms the comparative.

So:

• més forta = stronger
• literally: more strong

This is a very common pattern in Catalan:

• més gran = bigger
• més verda = greener
• més ràpid = faster

They help with pronunciation and correct spelling.

• ç in comença makes the c sound like s
• the accent in més is part of the correct spelling and also helps distinguish the word
• the accent in créixer shows the stressed syllable

These marks are not optional in standard writing.

Fulla is roughly pronounced like FOO-lya.

The ll in Catalan is not usually pronounced like a normal English l-l. In many accents it sounds similar to the lli / ly sound in million or brilliant, though exact pronunciation varies by dialect.

So a useful approximation for learners is:

fulla ≈ FOO-lya

The first part, Quan la planta comença a créixer, is an introductory time clause. The comma helps separate it from the main clause:

Quan la planta comença a créixer, cada fulla nova sembla més forta.

This punctuation is very natural and helps the sentence read clearly.