Learn Hardcore Finnish: Sato on hyvä tänä vuonna.

You’re not talking about a specific crop like wheat or potatoes; sato is the overall harvest/yield (unless the wider context specifies a certain plant).

Why is there no word for the in Sato on hyvä tänä vuonna?

Finnish has no articles (no words for a / an / the).

The bare noun sato can correspond to:

a harvest / a crop
the harvest / the crop
or even just harvest, without any article

Which English article you choose depends on the context, not on anything visible in the Finnish grammar.

In this particular sentence, natural translations would be:

The harvest is good this year.
The crop is good this year.

Finnish leaves that unspecified; English forces you to pick one.

What form is hyvä in, and why isn’t it changed in any way?

Hyvä is an adjective meaning good.

Here it’s used as a predicative adjective (part of the “X is Y” structure). In Finnish, predicative adjectives usually:

are in nominative singular (the basic dictionary form)
agree in number and case with the subject when the subject is in nominative

The subject is sato (nominative singular), so the adjective is also:

hyvä (nominative singular)

So Sato on hyvä = The harvest is good.

You could get other forms like hyvää (partitive) in sentences like:

Satoa on hyvää tänä vuonna. – The harvest is of good quality this year / There is good harvest this year.

But with a simple X on Y statement and a nominative subject, hyvä stays in its basic form.

What does on mean here, and why not olla?

Olla is the infinitive form of the verb “to be” – like English to be.

On is the 3rd person singular present tense form, corresponding to is.

olla = to be
on = (he / she / it / the harvest) is

So:

Sato on hyvä. – The harvest is good.

You can’t use the infinitive olla in a normal finite sentence; you need a conjugated form (on, oli, oli ollut, etc.) just like English uses is / was / has been instead of only to be.

Why doesn’t the sentence have a pronoun like se (it) before on?

In Finnish, you don’t need a subject pronoun when the subject is already a noun in the sentence.

Sato on hyvä.
Literally: Harvest is good.

The subject is sato, so a separate se (it) would be redundant.

You could say:

Se on hyvä tänä vuonna. – It is good this year.

That would usually refer back to something already mentioned (for example, a specific crop: the wheat crop), with se standing in for that noun.

But with an explicit subject (sato), you just say Sato on hyvä tänä vuonna, no pronoun needed.

What case is tänä vuonna, and what does the ending -nä mean?

Tänä vuonna is a common time expression meaning this year.

Grammatically:

tämä (this) → tänä (essive singular)
vuosi (year) → vuonna (essive singular)

So both words are in the essive case (ending -na / -nä), which often expresses:

a temporary state, role, or
in time expressions, something like “during X”

So tänä vuonna literally has a sense close to as this year / in this year / during this year, but in actual translation it’s just this year.

Finnish uses the essive case in a bunch of fixed time phrases:

tänä aamuna – this morning
tänä iltana – this evening
viime vuonna – last year (adjective + essive of vuosi)

Why isn’t it tällä vuonna or tässä vuodessa for “this year”?

Those would use different cases and would be incorrect for the normal “this year” expression.

tällä = adessive of tämä (“on this / at this”)
tässä = inessive of tämä (“in this”)
vuonna = essive of vuosi (“as year / in the role of year” in time expressions)

Finnish has set idiomatic patterns for time:

tänä vuonna – this year
tällä viikolla – this week (different pattern!)
tänä iltana – this evening
tällä kertaa – this time

So even though tällä vuonna might look like “on this year” by analogy, it’s not how Finns say this year. The fixed, correct phrase is tänä vuonna.

Can I change the word order to Tänä vuonna sato on hyvä? Does it change the meaning?

Yes, you can say:

Tänä vuonna sato on hyvä.

Both:

Sato on hyvä tänä vuonna.
Tänä vuonna sato on hyvä.

mean essentially The harvest is good this year.

The difference is about emphasis / focus, not basic meaning:

Sato on hyvä tänä vuonna.
– More neutral; starts by talking about the harvest, then adds this year as extra information.
Tänä vuonna sato on hyvä.
– Slight emphasis on this year (e.g., contrasting with other years: This year (at least), the harvest is good.)

Word order in Finnish is flexible, but it affects what feels like the “topic” and what’s being highlighted.

How would I say “The harvests are good this year” in the plural?

For plural:

sato → sadot (nominative plural)
hyvä → hyvät (nominative plural adjective)
on → ovat (3rd person plural of olla, “are”)

So:

Sadot ovat hyvät tänä vuonna.
= The harvests are good this year.

You still keep tänä vuonna unchanged; the time expression doesn’t care about the number of sato/sadot.

How would I say “The harvest was good last year” instead of “is good this year”?

You need to change both the tense and the time expression.

Present → past:
- on (is) → oli (was)
this year → last year:
- tänä vuonna → viime vuonna

So:

Sato oli hyvä viime vuonna.
= The harvest was good last year.

Structure is exactly parallel:

Sato on hyvä tänä vuonna. – The harvest is good this year.
Sato oli hyvä viime vuonna. – The harvest was good last year.

How do you pronounce sato, and is it easy to confuse with sata (one hundred) or sataa (to rain)?

Pronunciation:

sato: SA-to
- stress on the first syllable (SA)
- both a and o are short vowels

Related similar words:

sata (one hundred): SA-ta – same stress pattern; final vowel a, not o
sataa (to rain / it rains): SA-taa
- double aa = long a sound in the second syllable

In normal speech, context makes them clear:

Sato on hyvä tänä vuonna. – harvest context
Sata on iso luku. – number 100
Tänään sataa. – weather / rain

So they’re close in sound, but not usually confusing for native speakers.