Fræin spíra hraðar þegar veðrið er hlýtt og moldin er ekki of blaut.

Icelandic usually puts the definite article on the end of the noun instead of using a separate word like English the.

So here:

• fræin = the seeds
• veðrið = the weather
• moldin = the soil

The exact ending changes depending on gender, number, and case. That is why you see -in on one noun and -ið on another.

Here fræin is plural definite: the seeds.

The noun fræ is a neuter noun, and its basic form can look the same in singular and plural in some cases, so the article helps make things clearer:

• fræ = seed / seeds depending on context
• fræið = the seed
• fræin = the seeds

So in this sentence, fræin spíra clearly means the seeds sprout.

Because the subject fræin is plural, the verb is in the 3rd person plural present.

The verb is spíra = to sprout / germinate. In the present tense:

• ég spíra = I sprout
• þú spírar = you sprout
• hann/hún/það spírar = he/she/it sprouts
• við spírum = we sprout
• þið spírið = you all sprout
• þau spíra = they sprout

So fræin spíra means the seeds sprout.

Because hraðar is the comparative adverb here: faster.

It modifies the verb spíra—it tells you how the seeds sprout.

• hratt = fast, quickly
• hraðar = faster

So:

• Fræin spíra hratt = The seeds sprout quickly.
• Fræin spíra hraðar = The seeds sprout faster.

hraðari would usually be an adjective meaning faster before a noun, for example hraðari bíll = a faster car.

Here þegar means when and introduces a time clause:

• þegar veðrið er hlýtt... = when the weather is warm...

That suggests a condition that is presented as a real situation or typical circumstance.

ef means if and would sound more conditional or uncertain:

• ef veðrið er hlýtt... = if the weather is warm...

In this sentence, þegar fits better because it describes the situation in which seeds generally sprout faster.

Because there are really two linked clauses after þegar:

• veðrið er hlýtt = the weather is warm
• moldin er ekki of blaut = the soil is not too wet

They are joined by og = and.

Each clause needs its own verb, so you get:

• veðrið er hlýtt
• og moldin er ekki of blaut

That is completely normal in Icelandic.

Because hlýtt is the form of the adjective that agrees with veðrið, which is neuter singular.

The adjective hlýr = warm changes form depending on gender/number:

• masculine: hlýr
• feminine: hlý
• neuter: hlýtt

Since veðrið is neuter singular, Icelandic uses:

• veðrið er hlýtt = the weather is warm

This is adjective agreement, which is much stronger in Icelandic than in English.

Because blaut agrees with moldin, which is feminine singular.

The adjective blautur = wet changes like this in the singular:

• masculine: blautur
• feminine: blaut
• neuter: blautt

So:

• moldin er blaut = the soil is wet

If the noun were neuter, you would expect blautt instead.

It is not the same word as English of.

In Icelandic, of means too or overly.

So:

• of blaut = too wet
• ekki of blaut = not too wet

That is a very common Icelandic word, and English speakers often mistake it at first because it looks familiar.

No. Icelandic mold usually means soil, earth, or dirt.

So moldin here means the soil, not fungal mold.

This is a useful false friend to remember:

• Icelandic mold = soil/earth
• English mold = fungus growth

Yes. If the sentence starts with the subordinate clause, the main clause follows normal Icelandic verb-second word order.

Current order:

• Fræin spíra hraðar þegar veðrið er hlýtt og moldin er ekki of blaut.

With the when clause first:

• Þegar veðrið er hlýtt og moldin er ekki of blaut, spíra fræin hraðar.

Notice that in the main clause after the initial subordinate clause, the verb comes before the subject:

• spíra fræin not
• fræin spíra

That is a very important Icelandic word-order pattern.