Většina sazenic potřebuje vodu.

Většina means the majority or, in natural English, most.

So:

• většina sazenic = most seedlings / the majority of seedlings

Even though English often says most seedlings, Czech commonly uses the noun většina + another noun in the genitive.

Because většina is followed by the genitive plural.

The base noun is:

• singular: sazenice = seedling
• plural nominative: sazenice = seedlings
• genitive plural: sazenic

So:

• většina sazenic = most of the seedlings

This is a very common pattern in Czech:

• většina lidí = most people
• většina studentů = most students
• většina domů = most houses

Because the grammatical subject is většina, and většina is singular.

Even though the meaning refers to many seedlings, Czech treats většina as the head of the subject:

• Většina sazenic potřebuje vodu. = literally The majority of seedlings needs water.

So the verb agrees with většina, not with sazenic.

Compare:

• Sazenice potřebují vodu. = Seedlings need water.
  Here the subject is directly sazenice (plural), so the verb is plural: potřebují.

Because potřebovat (to need) takes a direct object in the accusative.

The noun is:

• nominative: voda = water
• accusative: vodu

So:

• potřebuje vodu = needs water

This is a normal object pattern:

• mít vodu = to have water
• kupovat vodu = to buy water
• potřebovat vodu = to need water

The dictionary form is potřebovat, meaning to need.

Potřebuje is:

• 3rd person singular
• present tense

So it means:

• he/she/it needs
• or in this sentence, the majority needs

A few present-tense forms are:

• potřebuji = I need
• potřebuješ = you need
• potřebuje = he/she/it needs
• potřebujeme = we need
• potřebujete = you (plural/formal) need
• potřebují = they need

In the sentence, the form sazenic is genitive plural.

The full noun pattern is:

• singular nominative: sazenice
• plural nominative: sazenice
• plural genitive: sazenic

This can feel tricky because sazenice looks the same in singular and plural nominative. You have to tell from context.

Here, because it follows většina, it must be genitive plural:

• většina sazenic = most seedlings

Většina is a feminine singular noun.

That matters because verbs in Czech agree with the subject. In the present tense, the singular form is enough for this sentence:

• většina ... potřebuje

In the past tense, you would see the feminine gender more clearly:

• Většina sazenic potřebovala vodu. = Most seedlings needed water.

Here potřebovala shows feminine singular agreement with většina.

Yes. That means:

• Seedlings need water

This is slightly different in nuance:

• Většina sazenic potřebuje vodu = Most seedlings need water
• Sazenice potřebují vodu = Seedlings need water / Seedlings need water in general

So the first sentence is more specific: not necessarily all seedlings, but the majority of them.

No, Czech word order is fairly flexible.

The neutral order here is:

• Většina sazenic potřebuje vodu.

But you could also say:

• Vodu potřebuje většina sazenic.
• Většina sazenic vodu potřebuje.

These versions shift emphasis:

• starting with vodu emphasizes water
• placing vodu before the verb can give it contrastive stress

For a learner, the original sentence is the most neutral and safest version.

Because Czech has no articles.

English says:

• most seedlings need water
• the majority of seedlings needs water

Czech simply says:

• Většina sazenic potřebuje vodu.

Whether something is the, a, or general is usually understood from context.

A rough pronunciation guide is:

• Většina ≈ vyet-shi-na
• sazenic ≈ sa-ze-nits
• potřebuje ≈ po-trzhe-bu-ye
• vodu ≈ vo-du

A few useful sound notes:

• ě often softens the consonant before it
• š sounds like sh
• c sounds like ts
• ř is the famous Czech sound, something like a rolled r mixed with zh

So potřebuje is often the hardest word here because of ř.

Yes, when it means majority/most of and is followed by the thing being counted, it normally takes the genitive:

• většina lidí = most people
• většina zvířat = most animals
• většina sazenic = most seedlings

This is a very useful pattern to learn as a chunk.

Here vodu means water as a substance, in a general sense.

Czech often uses the accusative singular of mass nouns this way:

• pít vodu = to drink water
• potřebovat vodu = to need water

It does not mean one specific unit like a water. Czech is simply talking about water in general.

A close breakdown is:

• Většina = majority / most
• sazenic = of seedlings
• potřebuje = needs
• vodu = water

So a very literal rendering would be:

• The majority of seedlings needs water

But the most natural English translation is:

• Most seedlings need water.