После дождя лужайка была мокрой, но очень зелёной.

Because после requires the genitive case. The dictionary form is дождь, but after после it changes to дождя.

So the pattern is:

после + genitive

Examples:

• после урока = after the lesson
• после обеда = after lunch
• после дождя = after the rain

Была is the past tense of быть = to be.

In the past tense, Russian verbs agree with the subject in gender and number:

• был = masculine
• была = feminine
• было = neuter
• были = plural

The subject here is лужайка, which is a feminine singular noun, so the verb is была.

After быть in the past tense, Russian often uses the adjective in the instrumental case to describe a state or condition.

So:

• мокрая → мокрой
• зелёная → зелёной

This is very common in sentences like this:

• Она была счастливой
• Дом был пустым
• Лужайка была мокрой

Here it presents the lawn as being in a certain condition after the rain.

Yes, that is possible.

Using the nominative adjective after была can sound more conversational or simply like a straightforward description. Using the instrumental is also very natural and is often felt to fit a temporary state especially well.

So both are possible:

• лужайка была мокрой, но очень зелёной
• лужайка была мокрая, но очень зелёная

The version with мокрой, зелёной is a very standard choice.

Because но means but, and in Russian it normally has a comma before it when it connects contrasting parts.

So:

• мокрой, но очень зелёной

This works much like English:

• wet, but very green

Russian regularly puts a comma before contrast words like но.

Russian word order is flexible. Putting После дождя first sets the scene right away: after the rain...

That makes the sentence feel natural because it introduces the circumstance before the description.

Other orders are possible, for example:

• Лужайка после дождя была мокрой, но очень зелёной

But starting with После дождя is a common and natural way to frame the sentence.

Russian has no articles, so there is no direct equivalent of the or a/an.

Whether лужайка means the lawn, a lawn, the little meadow, or a grassy patch depends on context.

That is normal in Russian:

• Книга на столе can mean The book is on the table or A book is on the table, depending on the situation.

Лужайка is a feminine noun meaning something like lawn, grassy patch, or little meadow.

It often has a slightly diminutive feel, as if referring to a pleasant small grassy area rather than a large field.

So it is not just a random grass-related word; it suggests a particular kind of small green space.

The letter ё is pronounced yo.

So зелёной is pronounced roughly like zee-LYO-noy.

The ё matters because it tells you both:

• the pronunciation
• the stress

In many printed texts, Russian writes е instead of ё, but the word is still understood as зелёной and pronounced with yo.

Очень means very. It is an adverb modifying the adjective зелёной.

So:

• очень зелёной = very green

In this sentence, очень directly intensifies зелёной, not мокрой.

If you wanted to intensify both adjectives, you could say something like:

• лужайка была очень мокрой, но очень зелёной

Because both adjectives agree with лужайка and are in the same grammatical form.

Лужайка is:

• feminine
• singular

And after была, the adjectives are used here in the instrumental singular feminine, so both take the same ending:

• мокрой
• зелёной

This agreement is one of the core features of Russian adjectives: they match the noun in gender, number, and case.