Nemoj posaditi sjeme preduboko.

In Croatian, negative commands are often formed with nemoj + infinitive.

So:

• Nemoj posaditi... = Don’t plant...

Using just ne directly with an imperative form is generally not the usual pattern here.

Compare:

• Posadi sjeme. = Plant the seed.
• Nemoj posaditi sjeme. = Don’t plant the seed.

So nemoj is the standard way to tell one person informally don’t do something.

This form is for one person, in an informal singular command.

If you are speaking to:

• one person informally: Nemoj posaditi sjeme preduboko.
• more than one person, or one person formally: Nemojte posaditi sjeme preduboko.

So the sentence you were given is the singular informal version.

This is about aspect, which is very important in Croatian.

• saditi = imperfective
• posaditi = perfective

Very roughly:

• saditi focuses on the process, repeated action, or general activity of planting
• posaditi focuses on completing the action: to plant as a finished act

In this sentence, posaditi is natural because the speaker is warning someone not to perform the action in a certain way: don’t plant it too deep.

You may also hear:

• Ne sadi sjeme preduboko.

That can also be natural, but it has a slightly different feel. It can sound more like a general instruction or ongoing advice.
Nemoj posaditi often sounds like don’t go and plant it too deep or make sure you don’t plant it too deep.

Here sjeme is in the accusative singular, because it is the direct object of the verb posaditi.

However, sjeme is a neuter noun, and in this case its nominative and accusative singular forms are the same:

• nominative: sjeme
• accusative: sjeme

So even though it is in the accusative, it looks unchanged.

Preduboko means too deep.

It is made from:

• pre- = too, overly
• duboko = deeply / deep

So:

• duboko = deeply
• preduboko = too deeply

In the sentence, it modifies the planting action:

• Nemoj posaditi sjeme preduboko.
• Don’t plant the seed too deep / too deeply.

Because in Croatian, this kind of pre- prefix is attached directly to the adjective or adverb.

So:

• dubok = deep
• predubok = too deep
• duboko = deeply / deep
• preduboko = too deeply / too deep

This is normal word formation in Croatian. It is not written as two separate words.

Here it is an adverb, because it describes how the seed is planted.

It modifies the verb phrase:

• posaditi sjeme preduboko = to plant the seed too deep

If it were describing a noun, you would use an adjective form instead. For example:

• Rupa je preduboka. = The hole is too deep.

But in your sentence, the meaning is about the action, so the adverb preduboko is the right form.

Croatian does not have articles like English a or the.

So sjeme can mean:

• a seed
• the seed
• sometimes even seed in a more general sense

The exact meaning depends on context.

That is why Croatian can say simply:

• posaditi sjeme

where English usually needs something like:

• plant the seed
• plant a seed

Yes, Croatian word order is more flexible than English word order.

The neutral, natural order here is:

• Nemoj posaditi sjeme preduboko.

But depending on emphasis, you could hear variations such as:

• Sjeme nemoj posaditi preduboko.
• Nemoj sjeme posaditi preduboko.

These alternatives can sound more marked or emphasize a certain word. For learners, the original version is the safest and most neutral one to use.

Yes, it can be correct and natural.

Compare:

• Nemoj posaditi sjeme preduboko.
• Ne sadi sjeme preduboko.

The difference is mostly about aspect and nuance:

• Nemoj posaditi: don’t perform that completed act in that way
• Ne sadi: don’t plant / don’t be planting, often more general or process-focused

In practical terms, both can work, but nemoj + infinitive is a very common and useful pattern for learners to know when giving negative commands.

Sjeme is pronounced approximately like SYEH-meh, with two syllables:

• sje-me

A few pronunciation tips:

• sj is like a soft sy sound
• je is pronounced roughly like ye
• stress can vary by dialect, but for a learner the key thing is to keep it clear and smooth

So a simple learner-friendly approximation is:

• SYEH-meh

Yes, it is completely natural.

It sounds like a practical instruction you might hear in gardening, farming, or planting advice.

It is concise and idiomatic:

• Nemoj = negative command
• posaditi = plant
• sjeme = seed
• preduboko = too deep

So this is a very good model sentence for learning how Croatian gives warnings or instructions.