Hækken langs vejen er blevet så høj, at vi næsten ikke kan se den gamle planke i hegnet.

A simple breakdown is:

• Hækken langs vejen = the subject, the hedge along the road
• er blevet = has become
• så høj = so high/tall
• at vi næsten ikke kan se ... = a result clause, that we can hardly see ...

So the overall pattern is:

• [something] has become so [adjective] that [result]

That pattern is very common in Danish:

• Det er så koldt, at jeg fryser.
• Han er blevet så træt, at han gik i seng.

Because hækken is the definite singular form: the hedge.

• hæk = a hedge
• hækken = the hedge

Danish often adds the definite article to the end of the noun instead of using a separate word like English the.

The same thing happens elsewhere in the sentence:

• vej → vejen = the road
• hegn → hegnet = the fence

They are related ideas, but they are not the same word:

• hæk = hedge, usually a row of bushes or shrubs
• hegn = fence or enclosure boundary

So in this sentence:

• Hækken langs vejen = the hedge along the road
• planke i hegnet = a plank in the fence

A learner might notice that English sometimes uses fence, hedge, barrier, or enclosure in overlapping ways, but Danish keeps hæk and hegn clearly separate here.

langs is a preposition meaning along.

So:

• langs vejen = along the road

And vejen is definite, meaning the road, not just a road.

This is very natural Danish:

• langs kysten = along the coast
• langs muren = along the wall

Because the verb blive meaning become normally forms its perfect tense as er blevet.

• bliver = becomes / is becoming
• blev = became
• er blevet = has become

So:

• Hækken er blevet høj = The hedge has become tall/high

This is something English speakers often just need to memorize: with blive in this meaning, Danish uses er blevet.

This is the Danish version of so ... that ...

• så høj = so tall/high
• at = that

So:

• så høj, at vi næsten ikke kan se ... = so high/tall that we can hardly see ...

This pattern is extremely common:

• Han er så træt, at han ikke kan arbejde.
• Det var så dyrt, at vi ikke købte det.

In Danish, høj covers both English high and tall in many situations.

So for a hedge, høj is perfectly natural.

Depending on context, English might translate it as:

• high
• tall

Danish does not split those two words the same way English does.

Literally, it means almost not, but in natural English it is often best translated as:

• hardly
• almost not
• can barely

So:

• vi næsten ikke kan se means
• we can hardly see or
• we can barely see

This is a very common Danish expression.

Because after at, you are in a subordinate clause, and Danish word order changes.

Compare:

• Main clause: Vi kan næsten ikke se den.
• Subordinate clause: ... at vi næsten ikke kan se den.

In subordinate clauses, words like ikke often come before the finite verb.

So English speakers often need to notice this contrast:

• Vi kan ikke se den.
• ... at vi ikke kan se den.

That is a key Danish word-order pattern.

kan se means can see and emphasizes ability or possibility.

Here that makes good sense: the hedge has grown so high that seeing the plank is difficult.

So:

• vi næsten ikke kan se ... = we can hardly see ...

If you said vi næsten ikke ser ..., that would be more like we hardly ever see ... or we scarcely see ..., which is a slightly different idea.

Because Danish uses a special pattern for definite nouns with adjectives.

Compare:

• planke = a plank
• planken = the plank

But when there is an adjective, Danish usually uses:

• den
  • adjective + noun

So:

• den gamle planke = the old plank

Not:

• den gamle planken

This is one of the most important noun patterns in Danish.

Because adjectives usually take -e in a definite noun phrase.

So:

• en gammel planke = an old plank
• den gamle planke = the old plank

Here, den makes the phrase definite, so the adjective becomes gamle.

This same pattern appears all the time:

• den store bil = the big car
• det lille hus = the small house
• de røde blomster = the red flowers

i usually means in, but in Danish it can also be used for something that is part of or within the structure of something.

So:

• en planke i hegnet = a plank in the fence

That sounds natural if the plank is one element of the fence itself.

In English, we might sometimes say in the fence or on the fence depending on the situation, but Danish i hegnet is very normal for something forming part of the fence.