Die Knospe an der Rose öffnet sich langsam, sobald die Sonne scheint.

Knospe is a feminine noun in German, so its basic article is die.

In this sentence, die Knospe is also the subject, so it is in the nominative case:

• die Knospe = the bud

A learner has to memorize the noun together with its gender:

• die Knospe
• die Rose
• die Sonne

German noun gender often does not match English logic, so it is best to learn the article as part of the word.

an der Rose means something like on the rose or attached to the rose.

Here it describes where the bud is located:

• die Knospe an der Rose = the bud on the rose

This sounds natural in German because a bud is thought of as being on the plant or flower. In English, we might sometimes say on the rose, on the rose plant, or just let context do the work.

Because an is followed here by the dative case.

An is a two-way preposition, which means it can take:

• accusative for direction or movement toward something
• dative for location or position

In this sentence, the bud is not moving toward the rose; it is located there. So German uses the dative:

• nominative: die Rose
• dative: der Rose

So:

• an der Rose = at/on the rose

In German, sich öffnen is a very common way to say to open when something opens by itself.

So:

• Die Tür öffnet sich. = The door opens.
• Die Blume öffnet sich. = The flower opens.

This is a reflexive construction. English often does not use a reflexive word here, but German often does.

You may also see öffnen used transitively:

• Er öffnet die Tür. = He opens the door.

So the difference is:

• etwas öffnen = to open something
• sich öffnen = to open / to open up

sich is the reflexive pronoun that belongs to öffnet.

Because the subject is die Knospe (third person singular), the reflexive pronoun is sich:

• ich öffne mich
• du öffnest dich
• er/sie/es öffnet sich

In this sentence, sich does not mean herself in a strong English sense. It is just part of the normal German way of saying that the bud opens.

German main clauses usually follow the verb-second rule.

The main clause here is:

• Die Knospe öffnet sich langsam

The first element is:

• Die Knospe

So the finite verb comes second:

• öffnet

Then the rest follows:

• sich langsam

That is why you get:

• Die Knospe | öffnet | sich langsam

This verb-second rule is one of the most important patterns in German main clauses.

Because sobald die Sonne scheint is a subordinate clause.

Words like sobald, weil, dass, wenn, and obwohl introduce subordinate clauses, and in subordinate clauses the conjugated verb usually goes to the end.

So:

• main clause: Die Sonne scheint.
• subordinate clause: ..., sobald die Sonne scheint.

That final placement of scheint is completely normal after sobald.

sobald means as soon as.

It shows that one thing happens immediately when another thing happens:

• ..., sobald die Sonne scheint = as soon as the sun shines

Compared with wenn:

• wenn can mean when or whenever
• sobald is more immediate and precise: as soon as

So:

• Wenn die Sonne scheint, öffnet sich die Knospe. = When/whenever the sun shines, the bud opens.
• Sobald die Sonne scheint, öffnet sich die Knospe. = As soon as the sun shines, the bud opens.

In German, subordinate clauses are usually separated from the main clause with a comma.

Since sobald die Sonne scheint is a subordinate clause, a comma is required:

• Die Knospe an der Rose öffnet sich langsam, sobald die Sonne scheint.

German uses commas more systematically than English in this kind of structure.

langsam is an adverb meaning slowly.

It describes how the bud opens:

• öffnet sich langsam = opens slowly

Its position is natural here, after the reflexive pronoun:

• Die Knospe öffnet sich langsam

German adverb placement is flexible, but this order sounds very normal and clear.

German often uses the present tense for:

• general truths
• repeated events
• descriptions of natural processes

So this sentence describes a general pattern:

• the bud opens slowly when the sun shines

That is why the present tense works well:

• öffnet
• scheint

English also often uses the present tense in the same kind of sentence:

• The bud opens slowly as soon as the sun shines.

Yes, absolutely.

You could say:

• Sobald die Sonne scheint, öffnet sich die Knospe an der Rose langsam.

When the subordinate clause comes first, the main clause still follows the verb-second rule. But now the whole subordinate clause counts as the first element, so the finite verb of the main clause comes immediately after it:

• Sobald die Sonne scheint, öffnet sich ...

You do not say:

• Sobald die Sonne scheint, die Knospe öffnet sich ...

That would be wrong.

Because an is the natural preposition for something attached to or located on the side/surface of something in this context.

A bud is thought of as growing on the rose, attached to it, so German uses:

• an der Rose

auf usually suggests something resting on top of a surface:

• auf dem Tisch = on the table

So auf der Rose would sound odd here.

It can often cover both ideas, depending on context.

German present tense is broader than English present simple. So:

• die Sonne scheint can mean the sun shines
• or the sun is shining

In this sentence, because it describes a condition for the bud opening, English will often translate it as a general statement:

• as soon as the sun shines

But context could make it feel more like is shining. German does not need a separate form here.