Сезонна полуниця вже стигла.

In Ukrainian, полуниця can be used as a mass/collective noun, like talking about strawberry produce in general. So Сезонна полуниця вже стигла can naturally mean Seasonal strawberries are already ripe.

If you want to emphasize individual strawberries, you can use the plural: Сезонні полуниці вже стиглі.

So the singular here does not always mean just one berry.

Because сезонна is an adjective agreeing with полуниця.

Полуниця is:

• feminine
• singular
• nominative

So the adjective must match it:

• masculine: сезонний
• feminine: сезонна
• neuter: сезонне
• plural: сезонні

Here, сезонна полуниця means seasonal / in-season strawberries.

Because it describes полуниця, so it agrees with that noun too.

In this sentence, стигла means ripe, and it matches the feminine singular noun полуниця:

• стиглий — masculine
• стигла — feminine
• стигле — neuter
• стиглі — plural

So:

• Сезонна полуниця вже стигла = feminine singular
• Сезонні полуниці вже стиглі = plural

For a learner, the most useful way to read it here is as an adjective: ripe.

So the sentence is basically: Сезонна полуниця вже (є) стигла
= Seasonal strawberries are already ripe

However, the form стигла can also be the past tense feminine singular of the verb стигнути: ripened / became ripe.

So the form is ambiguous by itself, but the intended meaning comes from context. If the meaning shown to you is a present state like is ripe, then treat it as an adjective here.

Because in Ukrainian, the present-tense verb to be is usually omitted.

English: The strawberries are ripe.

Ukrainian: Полуниця стигла.

So є is normally not used here. A sentence like Полуниця є стигла sounds unnatural in ordinary speech.

This is very common in Ukrainian:

• Вона гарна. = She is pretty.
• Чай гарячий. = The tea is hot.
• Полуниця стигла. = The strawberries are ripe.

It is in the nominative case, because it is the subject of the sentence.

You can see that the whole sentence is built around the subject: Сезонна полуниця — the seasonal strawberry / seasonal strawberries
вже стигла — is already ripe

Since сезонна and стигла both describe that subject, they also appear in forms that match nominative feminine singular.

Вже means already.

It shows that the state has been reached by now:

• Полуниця стигла. = The strawberries are ripe.
• Полуниця вже стигла. = The strawberries are already ripe.

It often appears before the word it highlights, but its position can be somewhat flexible.

Yes. Ukrainian word order is more flexible than English, because endings carry a lot of grammatical information.

The neutral order here is: Сезонна полуниця вже стигла.

You may also hear:

• Полуниця вже стигла.
• Вже стигла сезонна полуниця.

These can sound more emphatic, contextual, or literary depending on the situation.

Still, for a learner, Сезонна полуниця вже стигла is a very good neutral model.

Literally, сезонна means seasonal. In this context, it often corresponds to natural English in-season.

So depending on context, the idea is:

• seasonal strawberries
• in-season strawberries

Both capture the sense well.

A useful stressed version is:

сезо́нна полуни́ця вже сти́гла

Approximate pronunciation: seh-ZON-na po-loo-NY-tsya vzhé STY-hla

A few helpful notes:

• ж sounds like the s in measure
• ц sounds like ts
• Ukrainian г is usually a softer, voiced sound, closer to h than English hard g

So стигла does not sound like English stig-gla; the г is softer.

Then you would normally use the plural:

Сезонні полуниці вже стиглі.

That means The seasonal strawberries are already ripe, with clear emphasis on multiple individual berries.

Compare:

• Сезонна полуниця вже стигла. — strawberries as produce / a collective mass
• Сезонні полуниці вже стиглі. — individual strawberries, plural