På balkongen har hon satt ett frö i mörk jord.

This is because Swedish follows the V2 rule in main clauses: the finite verb must come in the second position.

So if you start with the subject, you get:

• Hon har satt ett frö i mörk jord på balkongen.

But if you move another element to the front for emphasis, like På balkongen, then the verb must still stay second:

• På balkongen har hon satt ett frö i mörk jord.

So the order becomes:

1. På balkongen
2. har
3. hon
4. the rest of the sentence

This kind of inversion is very common in Swedish.

The ending -en is the definite article attached to the noun.

• en balkong = a balcony
• balkongen = the balcony

Swedish usually adds definiteness to the end of the noun instead of using a separate word like English the.

So På balkongen literally means On the balcony.

Swedish uses på with surfaces and many open areas or platforms, and a balcony is normally treated as something you are on, not in.

So:

• på balkongen = on the balcony

Using i would sound wrong here, because a balcony is not thought of as an enclosed container in normal usage.

Har satt is the perfect tense, which is formed with:

• har
  • supine

Here:

• har = has
• satt = supine form of sätta

So:

• hon har satt = she has put/planted

If you used satte, that would be the simple past:

• hon satte ett frö i mörk jord = she put/planted a seed in dark soil

English often uses both she planted and she has planted, depending on context. Swedish makes the same kind of distinction.

Here it comes from sätta, not sitta.

That can be confusing, because the forms look similar.

For sätta:

• infinitive: sätta = to put, set
• present: sätter
• past: satte
• supine: satt

For sitta:

• infinitive: sitta = to sit
• present: sitter
• past: satt

So satt can belong to either verb, depending on context. In this sentence, because it comes after har, it is the supine of sätta.

Because frö is an ett-word in Swedish.

Swedish nouns have two grammatical genders:

• en-words
• ett-words

So:

• ett frö = a seed
• fröet = the seed

You simply have to learn the gender of each noun. Unfortunately, it is not always predictable.

Here jord is being used as an uncountable/material noun, similar to English soil or earth.

So i mörk jord means:

• in dark soil

It is indefinite and general, not referring to one specific batch of soil. That is why there is no definite article.

Compare:

• i mörk jord = in dark soil
• i den mörka jorden = in the dark soil

The first is general; the second points to a specific soil.

Because the noun phrase is indefinite and jord is an en-word.

In Swedish adjective agreement, the basic pattern is:

• en-word, indefinite singular: mörk
• ett-word, indefinite singular: mörkt
• plural / definite: mörka

So:

• mörk jord = dark soil
• mörkt frö = dark seed
• mörka frön = dark seeds
• den mörka jorden = the dark soil

In this sentence, i can feel like either in or into in English, depending on how you express the action.

• satt ett frö i mörk jord = put/planted a seed in dark soil

Swedish often uses i where English might choose in or into depending on the verb and context. The important idea is that the seed ends up inside the soil.

It is understandable, but it is not the most specific verb.

Some common choices are:

• så ett frö = sow a seed
• plantera = plant
• sätta = put/set/place

So hon har satt ett frö i mörk jord suggests that she put or planted a seed in dark soil. A more specifically gardening-oriented version might be:

• Hon har sått ett frö i mörk jord.

That said, the given sentence is still easy to understand.

Yes. That version is also grammatical.

The difference is mainly focus:

• På balkongen har hon satt ett frö i mörk jord.
  Emphasizes where this happened.

• Hon har satt ett frö i mörk jord på balkongen.
  Starts more neutrally with the subject hon.

So moving På balkongen to the front highlights the location.

A very neutral version would be:

• Hon har satt ett frö i mörk jord på balkongen.

This starts with the subject, which is often the default in Swedish. The original sentence sounds slightly more marked because it puts the location first for emphasis.

Both are correct; the choice depends on what you want to highlight.