Если будет тепло, бутон раскроется завтра.

This is a very common difference between English and Russian.

In Russian, after если (if), you can use the future tense when the condition is about the future:

• Если будет тепло, бутон раскроется завтра.

Literally, this is closer to:

• If it will be warm, the bud will open tomorrow.

But that sounds unnatural in English, so English changes it to:

• If it is warm, the bud will open tomorrow.

So the Russian sentence is completely normal. Russian and English simply handle future conditions differently.

Because тепло here is not an adjective describing a noun. It is a predicative word meaning warm in the sense of the weather / the environment is warm.

Russian often uses words like this for weather and general conditions:

• Сегодня тепло. = It’s warm today.
• Было холодно. = It was cold.
• Будет темно. = It will be dark.

If you say тёплый, that adjective needs a noun:

• тёплый день = a warm day
• тёплый чай = warm tea

So:

• будет тепло = it will be warm
• будет тёплый by itself is incomplete or unnatural

Будет is the 3rd person singular future form of быть (to be).

Here it means it will be:

• будет тепло = it will be warm

Russian often leaves out a subject like English it in weather expressions. So there is no separate word for it here.

Because Если будет тепло is a subordinate clause introduced by если (if), and Russian normally separates subordinate clauses with a comma.

So the structure is:

• Если будет тепло, = conditional clause
• бутон раскроется завтра. = main clause

This comma is required in standard Russian writing.

Раскроется comes from раскрыться, which means to open up, to unfold, to blossom/open depending on context.

For a bud, раскрыться is very natural, because it suggests opening naturally from within.

Why not раскроет? Because раскроет is the non-reflexive verb раскрыть and usually needs an object:

• Он раскроет книгу. = He will open the book.

But a bud opens by itself, so Russian uses the reflexive verb:

• бутон раскроется = the bud will open

Could откроется be possible in some contexts? Sometimes yes, but раскроется is especially natural for flowers, buds, petals, wings, etc., where something unfolds.

The -ся marks the verb as reflexive. But in Russian, reflexive verbs are not always literally reflexive in the English sense of it opens itself.

Here, раскрыться means something like:

• to open
• to unfold
• to open up

So бутон раскроется is simply the normal way to say that the bud opens.

A useful contrast:

• раскрыть бутон = to open a bud / to make a bud open
• бутон раскроется = the bud will open

Раскроется is a perfective verb in the future.

That matters because perfective verbs in Russian usually describe a single completed event:

• раскроется = will open / will have opened up

In this sentence, the idea is that the bud will reach the result of opening tomorrow.

If you used an imperfective verb, the meaning would be different or less natural here. Russian prefers the perfective because it is talking about the bud’s opening as one completed event.

So:

• раскроется завтра = it will open tomorrow / it will come open tomorrow

Because бутон is the subject of the sentence, so it is in the nominative case.

Structure:

• бутон = subject
• раскроется = verb

So:

• бутон раскроется = the bud will open

If бутон were an object, its form might change depending on the verb and case.

Yes. Russian word order is more flexible than English, although the original order is perfectly natural.

Original:

• Если будет тепло, бутон раскроется завтра.

You could also say:

• Если будет тепло, завтра бутон раскроется.
• Бутон раскроется завтра, если будет тепло.

These all mean roughly the same thing. The differences are mainly about emphasis.

For example:

• завтра earlier in the sentence can emphasize tomorrow
• putting the если clause at the end can make the main event come first

No. The word here is тепло.

It is related to тёплый (warm), but the form used in this sentence is always тепло.

So:

• тёплый день = a warm day
• сегодня тепло = it is warm today

This is normal and not a spelling simplification.

In practice, завтра most naturally goes with the main verb:

• бутон раскроется завтра = the bud will open tomorrow

So it tells you when the opening will happen.

The condition если будет тепло sets the circumstance, while завтра gives the time of the main event.

Yes, but the meaning changes slightly.

• Если будет тепло, бутон раскроется завтра.
  = If it is warm tomorrow / if it turns out warm, the bud will open tomorrow.

• Если тепло, бутон раскроется завтра.
  can sound more general or more immediate depending on context, but for a clearly future condition, будет is usually better.

Since the sentence is talking about a future condition connected with tomorrow, если будет тепло is the most natural choice.

A few useful points:

• если → stress on the first syllable: Ес-ли
• будет → stress on the first syllable: БУ-дет
• тепло → stress on the second syllable: теп-ЛО
• бутон → stress on the second syllable: бу-ТОН
• раскроется → stress on кро: рас-КРО-ет-ся
• завтра → stress on the first syllable: ЗА-втра

A learner may also notice that -тся / -ться in verbs is pronounced with a ца-like sound in standard speech, so раскроется sounds roughly like раскроеца, even though it is spelled -тся.