Við vonum að engin planta visni meðan við erum í fríi, svo nágranninn vökvar fyrir okkur.

Because visni is the present subjunctive of visna (to wither / wilt), while visnar is the present indicative.

After verbs like vona (to hope), Icelandic often uses the subjunctive in a subordinate clause introduced by að, especially when the situation is uncertain or wished for rather than stated as a fact.

So:

• við vonum að engin planta visni = we hope that no plant will wither / that no plant withers
• visnar would sound more like a plain factual statement

Because planta is a feminine noun.

The word enginn (no / none / not any) has to agree with the noun in gender, number, and case.

Here:

• planta = feminine singular
• nominative singular feminine of enginn = engin

So:

• engin planta = no plant

Compare:

• enginn maður = no man
• engin planta = no plant
• ekkert barn = no child

Engin planta means not a single plant. Icelandic often uses the singular this way when talking about the absence of even one item.

So the sentence focuses on each plant individually:

• engin planta visni = that no plant withers

You could also say engar plöntur visni (no plants wither), but that feels slightly different in emphasis. The singular can sound a bit more like not one single plant.

Here að introduces a subordinate clause, like English that:

• Við vonum að ... = We hope that ...

So:

• Við vonum að engin planta visni = We hope that no plant withers / will wither

In everyday English, that is often omitted, but in Icelandic að is normally kept in this kind of sentence.

No, the subject is normally stated again.

The first við belongs to the main clause:

• Við vonum ... = We hope ...

The second við belongs to the subordinate clause:

• meðan við erum í fríi = while we are on vacation

Icelandic does not normally drop the subject here just because it was mentioned earlier.

Í fríi is the normal Icelandic expression for being on vacation / off work / on a break.

So:

• vera í fríi = to be on vacation

This is an idiomatic expression, and fríi is in the dative here.

Even though English says on vacation, Icelandic uses í in this expression.

Meðan means while.

So:

• meðan við erum í fríi = while we are on vacation

This clause describes the time period during which the hoped-for situation applies.

Also, notice that after meðan, the word order is normal subordinate-clause order:

• við erum = we are

Icelandic main clauses often follow a verb-second pattern, but subordinate clauses like this do not force that same kind of inversion.

Here svo means so / therefore.

It connects the two ideas:

• We hope no plant withers while we’re away,
• so the neighbor waters for us.

So svo here introduces the result or practical consequence.

This is different from svo að, which more often means so that.

So in this sentence:

• svo nágranninn vökvar fyrir okkur = so the neighbor waters for us

Because nágranninn means the neighbor.

Icelandic usually adds the definite article to the end of the noun:

• nágranni = a neighbor
• nágranninn = the neighbor

So this sentence is talking about a specific, known neighbor, not just any neighbor.

The object is understood from context: presumably the plants.

Icelandic, like English, can omit an object when it is obvious.

So:

• nágranninn vökvar fyrir okkur literally means the neighbor waters for us
• In natural English, you would often understand the plants without needing to say it

If you wanted to make it explicit, you could say something like:

• nágranninn vökvar plönturnar fyrir okkur = the neighbor waters the plants for us

It means for us.

So:

• nágranninn vökvar fyrir okkur = the neighbor waters for us

The idea is that the neighbor is doing this as a favor or in our place.

This is a very common use of fyrir to express benefit or service done on someone’s behalf.

Here visna is intransitive.

That means the plant itself is the one undergoing the change:

• plantan visnar = the plant withers / wilts

There is no object. The plant is not withering something else; it is withering itself.

That is why engin planta is the subject of visni.

Sometimes learners will encounter variation, but in a sentence like this, the subjunctive is the expected and most natural choice because it expresses a hope about something uncertain.

So:

• Við vonum að engin planta visni is the form a learner should aim for.

Using the indicative here would sound less natural in standard usage, because the clause is not presenting a settled fact.

It is in the nominative singular.

That is because it is the subject of visni:

• engin planta visni = no plant withers

Both words show nominative singular feminine agreement:

• engin = nominative singular feminine
• planta = nominative singular

It breaks down like this:

• Við vonum = main clause: We hope
• að engin planta visni = subordinate clause after að: that no plant withers
• meðan við erum í fríi = time clause: while we are on vacation
• svo nágranninn vökvar fyrir okkur = result/consequence: so the neighbor waters for us

So the overall logic is:

1. we hope the plants stay fine,
2. during the time we are away,
3. so the neighbor takes care of the watering.