Высокая сосна и старая берёза отражались в большой луже после дождя.

Because they are adjectives agreeing with feminine singular nouns in the nominative case.

• сосна is feminine singular, so высокая must also be feminine singular nominative.
• берёза is also feminine singular, so старая matches it the same way.

This is basic adjective agreement in Russian: adjectives must match the noun in gender, number, and case.

In dictionary form, many Russian nouns ending in -а or -я are feminine, and both сосна and берёза follow that pattern.

So:

• сосна = feminine
• берёза = feminine

That is why the adjectives are feminine too: высокая сосна, старая берёза.

Because the subject is actually two things together:

• высокая сосна
• и старая берёза

When two singular nouns are joined by и (and), they form a plural subject, so the verb must be plural.

That is why Russian uses отражались, not отражалась.

Russian past tense is built from the infinitive stem plus endings that show gender or number.

The infinitive is отражаться.

Past forms:

• отражался = masculine singular
• отражалась = feminine singular
• отражалось = neuter singular
• отражались = plural

Since the subject is plural (the pine and the birch), the sentence uses отражались.

The -сь is the reflexive ending, a variant of -ся.

In this sentence, отражаться means to be reflected or to reflect oneself / appear reflected.

So отражались does not mean that the trees were reflecting something else. It means they themselves were visible as reflections in the puddle.

A useful contrast:

• отражать = to reflect something
• отражаться = to be reflected / to appear reflected

Because after в meaning in, Russian usually uses the prepositional case when talking about location.

Dictionary forms:

• большая лужа

Prepositional forms:

• в большой луже

Both the adjective and the noun change:

• большая → большой
• лужа → луже

So в большой луже means in a big puddle.

Because после always requires the genitive case.

Dictionary form:

• дождь = rain

Genitive form:

• дождя

So:

• после дождя = after the rain

This is a very common pattern in Russian:

• после урока = after the lesson
• после работы = after work
• после дождя = after the rain

Russian has no articles. There is no direct equivalent of English a/an or the.

Whether something is understood as a, the, or just a general noun depends on:

• context
• word order
• emphasis
• the broader situation

So в большой луже can mean:

• in a big puddle
• in the big puddle

depending on context.

Yes. Russian word order is more flexible than English because case endings show grammatical relationships.

The given order is natural and descriptive:

Высокая сосна и старая берёза отражались в большой луже после дождя.

It presents:

1. the things being described,
2. what they were doing,
3. where,
4. when/under what circumstances.

You could rearrange it for emphasis, for example:

• После дождя высокая сосна и старая берёза отражались в большой луже.
• В большой луже после дождя отражались высокая сосна и старая берёза.

These are still grammatical, but the focus changes slightly.

Yes. Старый / старая / старое can describe age for people, objects, and plants, including trees.

So старая берёза naturally means an old birch tree.

In Russian, using старый for a tree is completely normal.

The letter ё shows both:

• the sound yo
• the stressed syllable

So берёза is pronounced roughly bye-RYO-zuh, with stress on ё.

In many printed texts, Russian sometimes replaces ё with е, so you may see береза. But the correct spelling is берёза, and the pronunciation does not change.

For learners, ё is very helpful because it tells you exactly where the stress goes.

The singular в большой луже means the pine and the birch were reflected in one big puddle.

Russian could use the plural if the meaning were different, for example if reflections appeared in multiple puddles:

• в больших лужах = in big puddles

But in this sentence, the image is of one particular puddle after the rain, so singular is the natural choice.

Отражались is imperfective.

The imperfective is used because the sentence describes a scene or ongoing state, not a completed one-time event. It is like painting a picture:

• there was a tall pine and an old birch
• they were reflected in a large puddle
• this was after the rain

A perfective verb would suggest a more bounded, completed action, which is not the point here. The sentence is descriptive, so imperfective fits very well.