Độ ẩm còn ổn, nên hạt giống nảy mầm.

Độ ẩm is a noun meaning humidity or moisture level.

A helpful breakdown is:

• độ = degree, level
• ẩm = damp, moist, humid

So độ ẩm is literally something like the level of moisture. In a sentence about seeds, it often refers to the moisture conditions needed for germination, not just air humidity in a weather sense.

Here, còn means still.

So còn ổn means still okay, still fine, or still acceptable.

It suggests that the moisture level has remained good enough up to this point. Without còn, ổn would just mean okay/fine. Adding còn gives the idea of continuity.

Ổn is a very common Vietnamese adjective meaning okay, fine, acceptable, or stable.

In this sentence, it means the moisture level is good enough or within an acceptable range. It does not necessarily mean perfect; it just means there is no problem.

This word is very common in everyday speech, and it often sounds more natural and conversational than a more technical adjective.

Vietnamese often does not use a copula like English is/are before adjectives.

So instead of saying something literally equivalent to The humidity is still okay, Vietnamese just says:

• Độ ẩm còn ổn
  literally: moisture level still okay

This is completely normal. Adjectives can act as the predicate by themselves.

No. In this sentence, nên means so, therefore, or as a result.

This is a very important point, because nên can also mean should in other sentences.

Compare:

• Độ ẩm còn ổn, nên hạt giống nảy mầm.
  Here nên = so / therefore

• Bạn nên tưới cây.
  Here nên = should

A good clue is the structure. When nên connects two clauses after a pause or comma, it often means so / therefore.

The comma separates the cause from the result:

• Độ ẩm còn ổn = cause
• nên hạt giống nảy mầm = result

So the comma helps show the sentence structure clearly. In writing, this is very common with nên when it links two full ideas.

Hạt is a broad word that can mean seed, grain, kernel, bean, or other small roundish things depending on context.

Hạt giống is more specific. It means seed for planting or seed stock.

So in this sentence, hạt giống makes it clear that we are talking about seeds that can germinate, not just any grain or small particle.

Vietnamese nouns usually do not change form for singular or plural.

So hạt giống can mean:

• a seed
• seeds

The exact number depends on context.

If Vietnamese wants to be more specific, it can add words such as:

• một hạt giống = one seed
• những hạt giống = seeds
• các hạt giống = the seeds / seeds in general

In your sentence, it is most naturally understood as seeds in a general sense.

Nảy mầm is a fixed expression meaning to germinate or to sprout.

The parts are:

• nảy = to spring out, emerge
• mầm = sprout, bud, shoot

Together, nảy mầm describes the process of a seed beginning to grow. It is best learned as one vocabulary item.

So even though it has two words, you should think of it as one common verb phrase.

It could be either, depending on context.

Vietnamese often does not mark tense explicitly. So this sentence can mean:

• a present situation
• a general statement
• a described result in context

If the speaker wants to make time clearer, Vietnamese can add time words or aspect markers such as:

• đã = already / past
• đang = currently
• sẽ = will

But without them, Vietnamese often relies on context.

Yes. A very natural alternative is:

• Hạt giống nảy mầm vì độ ẩm còn ổn.

This version uses vì = because.

The difference is mostly about emphasis:

• Độ ẩm còn ổn, nên hạt giống nảy mầm.
  Focuses first on the condition, then gives the result.

• Hạt giống nảy mầm vì độ ẩm còn ổn.
  Focuses first on the result, then explains the reason.

Both are natural.