Moram presaditi ovu presadnicu.

Because it comes after moram (I must / I have to). In Croatian, modal verbs like morati are normally followed by an infinitive:

• Moram ići. = I have to go.
• Moram učiti. = I have to study.
• Moram presaditi ovu presadnicu. = I have to transplant this seedling.

So presaditi is not conjugated here because moram is already the finite verb.

Moram means I must or I have to.

It is the 1st person singular present tense of the verb morati (to have to / must).

A few forms of morati are:

• moram = I must
• moraš = you must
• mora = he/she/it must
• moramo = we must
• morate = you must
• moraju = they must

So the sentence starts with Moram... = I have to...

This is a very useful question, because the meaning changes with the prefix.

• saditi = to plant
• presaditi = to transplant / replant

The prefix pre- often adds the idea of moving, doing again, or changing from one place/state to another. Here, presaditi means taking a plant from one place and putting it somewhere else.

So:

• saditi cvijeće = to plant flowers
• presaditi biljku = to transplant a plant

Because ovu presadnicu is the direct object of the verb, so it must be in the accusative case.

The basic nominative form is:

• ova presadnica = this seedling

But in the sentence, the seedling is what the speaker must transplant, so Croatian uses the accusative:

• ovu presadnicu = this seedling (as the object)

For feminine singular nouns and adjectives/pronouns, this change is very common:

• ova kuća → ovu kuću
• ova biljka → ovu biljku
• ova presadnica → ovu presadnicu

Presadnicu is accusative singular.

The noun presadnica is a feminine noun ending in -a in the nominative singular. Feminine nouns of this type usually form the accusative singular by changing -a to -u:

• presadnica → presadnicu
• biljka → biljku
• sadnica → sadnicu

The demonstrative ova also changes to match:

• ova → ovu

So:

• nominative: ova presadnica
• accusative: ovu presadnicu

Presadnica means a seedling, young plant, or sometimes a transplant in the gardening sense.

It usually refers to a young plant that has been grown first and is then planted or transplanted elsewhere, for example into a garden bed or larger pot.

Depending on context, English might translate it as:

• seedling
• young plant
• transplant

So in this sentence, the natural English meaning is something like I have to transplant this seedling.

Because they are closely related words built from the same root.

They both come from the idea of saditi (to plant):

• presaditi = to transplant
• presadnica = a seedling / transplant

You can think of presadnica as a noun formed from the same plant-related root, with the suffix -nica.

This kind of word family is very common in Croatian, and noticing these connections can help vocabulary learning.

Yes, presaditi is generally perfective.

That matters because Croatian verbs often come in aspect pairs:

• presađivati = imperfective, ongoing/repeated transplanting
• presaditi = perfective, one completed transplanting action

In this sentence, presaditi fits well because the speaker is talking about completing a specific action: transplanting this particular seedling.

So the sentence suggests I need to get this done rather than focusing on the process itself.

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

The neutral/default order here is:

• Moram presaditi ovu presadnicu.

But you could also say:

• Ovu presadnicu moram presaditi.

That version puts extra emphasis on ovu presadnicu (this seedling), as if contrasting it with something else.

Even though the word order can change, the case endings still show the grammatical role, so the meaning remains clear.

A rough pronunciation guide is:

• Moram ≈ MO-ram
• presaditi ≈ pre-SA-di-ti
• ovu ≈ O-vu
• presadnicu ≈ pre-SAD-ni-tsu

A rough full pronunciation in English-style spelling could be:

MO-ram pre-SA-di-ti O-vu pre-SAD-ni-tsu

A few useful sound notes:

• c in Croatian is like ts in cats
• u is usually like oo in food, but shorter
• Croatian spelling is quite phonetic, so words are usually pronounced close to how they are written

Yes, absolutely.

• ovu presadnicu = this seedling / this transplant
• ovu biljku = this plant

Biljka is more general, while presadnica is more specific and suggests a young plant or seedling meant for transplanting.

So both are possible, but presadnicu is more precise in a gardening context.