haru ni naru to, kawa no tikaku no sakura ga kirei ni sakimasu.

に marks a point in time here, so 春に means in spring.

In this sentence, though, it is part of 春になると, not just 春に by itself. So the idea is not simply in spring, but more specifically:

• 春になる = to become spring
• 春になると = when it becomes spring / when spring comes

So に is attached to 春 because なる often uses X に なる to mean become X.

Literally, it means when it becomes spring.

Breakdown:

• 春 = spring
• に = marks the result/state with なる
• なる = become
• と = when / whenever

So 春になると gives the sense of:

• when spring comes
• whenever it becomes spring

It often sounds like a general seasonal pattern, not just one single occasion.

Because the nuance is slightly different.

• 春に、川の近くの桜がきれいに咲きます。
  = In spring, the cherry blossoms near the river bloom beautifully.

• 春になると、川の近くの桜がきれいに咲きます。
  = When spring comes, the cherry blossoms near the river bloom beautifully.

The second version emphasizes the change of season and the idea that this happens regularly whenever spring arrives.

So 春になると sounds a little more vivid and seasonal.

Here, と is a conditional particle meaning something like:

• when
• whenever
• if (in a natural/result sense)

In this sentence, it connects:

• 春になる = spring comes
• 桜がきれいに咲きます = the cherry blossoms bloom beautifully

So the meaning is:
When spring comes, the cherry blossoms bloom beautifully.

A useful nuance: と often implies a natural, automatic, or habitual result. That fits well here, because cherry blossoms blooming in spring is a normal seasonal event.

This is a very common Japanese structure.

Break it into pieces:

• 川 = river
• 川の近く = near the river
• 川の近くの桜 = the cherry blossoms near the river

The first の links river and near:

• 川の近く = the vicinity of the river / near the river

The second の links that whole phrase to 桜:

• 川の近くの桜 = the cherry blossoms that are near the river

So you can think of it as: [river] + [near] + [cherry blossoms]

Because 桜 is the grammatical subject of 咲きます.

• 桜が咲きます = the cherry blossoms bloom

Here, が marks the thing that performs or undergoes the action/state of the verb.

Why not は?
You could use は, but the nuance would change.

• 桜がきれいに咲きます = focuses on the cherry blossoms as the subject of the event
• 桜はきれいに咲きます = sounds more like a topic, possibly with contrast or broader commentary

In this sentence, が is the most natural choice for simply describing what happens when spring comes.

Because きれい is modifying the verb 咲きます, not directly modifying the noun 桜.

Compare:

• きれいな桜 = beautiful cherry blossoms
  (きれい modifies the noun 桜)

• きれいに咲きます = bloom beautifully
  (きれい modifies the verb 咲きます)

Since きれい is a na-adjective, it changes like this:

• before a noun: きれいな
• before a verb: きれいに

So きれいに咲きます means bloom beautifully.

Yes, that is a good way to understand it.

• 咲きます = bloom
• きれいに = beautifully / in a pretty way

So together:

• きれいに咲きます = bloom beautifully

In natural English, translations may vary:

• The cherry blossoms bloom beautifully
• The cherry blossoms bloom in beautiful form
• The cherry blossoms come out beautifully

But bloom beautifully is the most direct match.

咲きます means bloom or blossom. It is an intransitive verb.

That means the flower itself blooms:

• 桜が咲きます = The cherry blossoms bloom

By contrast, 咲かせます is the transitive/causative-related form meaning make something bloom or cause something to bloom.

For example:

• 花を咲かせます = make the flowers bloom

In your sentence, the cherry blossoms are doing the blooming themselves, so 咲きます is correct.

Because Japanese normally puts the main verb at the end.

The basic pattern is often:

• time/topic + place/modifiers + subject/object + verb

So this sentence is structured like:

• 春になると = when spring comes
• 川の近くの桜が = the cherry blossoms near the river
• きれいに = beautifully
• 咲きます = bloom

This final-verb structure is one of the biggest differences from English word order.

It usually sounds like a general seasonal truth or a habitual event.

That feeling comes mainly from:

• 春になると = whenever spring comes
• 咲きます in non-past polite form

So the sentence naturally suggests:

• When spring comes, the cherry blossoms near the river bloom beautifully.

In other words, this is probably describing a repeated pattern, not just one single event.

If you wanted to make it feel more like one specific past event, you would normally change the tense and probably the phrasing too.

Yes, depending on context.

• 川の近く = near the river
• 近く by itself can mean nearby, the vicinity, or near

In this sentence, 川の近くの桜 is most naturally:

• the cherry blossoms near the river
• the cherry blossoms by the river

So nearby is related in meaning, but near the river is the clearest translation here.

Because 咲きます is the polite -ます form.

Japanese often uses polite style in:

• textbooks
• everyday conversation with neutral politeness
• descriptions and explanations

The plain form would be:

• 春になると、川の近くの桜がきれいに咲く。

That is not wrong. It is just less polite and more plain/dictionary style.

So the sentence uses 咲きます simply because it is written in polite style.