Čtyři sazenice jsou na záhonu.

Because sazenice has the same form in the nominative singular and nominative plural.

So by itself, sazenice could mean a seedling or seedlings. In this sentence, you know it is plural because of:

• čtyři = four
• jsou = plural form of to be

Czech often lets the surrounding words show the number.

After dva, tři, čtyři (two, three, four), Czech normally uses the noun in the nominative/accusative plural.

So:

• čtyři sazenice = correct
• čtyři sazenic = not correct here

But with five and above, Czech usually switches to the genitive plural:

• pět sazenic

That is one of the big number patterns Czech learners have to get used to.

Because čtyři sazenice behaves like a plural subject, so the verb agrees in the plural:

• Čtyři sazenice jsou ...

This is the normal pattern with 2, 3, 4.

Compare that with 5 and above, where Czech often uses a different structure:

• Pět sazenic je na záhonu.

So this sentence is a good example of the 2–4 pattern.

Záhonu is the locative singular of the dictionary form záhon.

It appears in the locative because of the preposition na when na expresses a location:

• na záhonu = on/in the flowerbed

So:

• dictionary form: záhon
• locative singular: záhonu

The ending -u is the locative ending for this masculine noun.

Because this sentence describes location, not movement.

With na:

• na záhonu = on/in the flowerbed, already there → locative
• na záhon = onto the flowerbed, movement toward it → accusative

So if the idea is the seedlings are on the flowerbed, you need na záhonu.

Because Czech and English do not always use prepositions the same way.

For a garden bed or flowerbed, Czech normally says:

• na záhonu

Even if English often says in the flowerbed, Czech treats it more like a surface or garden plot. So na is the natural Czech choice.

This is a very common kind of difference between English and Czech: you usually cannot translate prepositions one-for-one.

Yes. That is completely correct.

Czech word order is flexible, and different word orders change the focus or emphasis more than the basic meaning.

• Čtyři sazenice jsou na záhonu.
  Neutral, straightforward statement about the seedlings.

• Na záhonu jsou čtyři sazenice.
  Often more natural if you are saying what is there in that place, similar to English There are four seedlings in the flowerbed.

Both are good Czech.

Normally, yes, you need jsou.

Czech usually keeps the present tense of být (to be) in sentences like this:

• Čtyři sazenice jsou na záhonu.

Without jsou, the sentence would usually sound incomplete, unless it were:

• a note
• a caption
• a list item
• very elliptical speech

So for normal full sentences, keep jsou.

Because Czech does not have articles.

So Czech does not separately mark:

• a seedling
• the seedling
• seedlings
• the seedlings

Instead, Czech relies on context.

That means na záhonu could correspond to English on the flowerbed, in the flowerbed, or sometimes on a flowerbed, depending on the situation.

They are:

• sazenice — dictionary form: sazenice, gender: feminine
• záhon — dictionary form: záhon, gender: masculine inanimate

This matters because gender affects declension and agreement elsewhere in the language.

For example:

• na záhonu shows a masculine locative form
• sazenic would be the genitive plural of sazenice

It does change.

In this sentence, čtyři is in the nominative, because it is part of the subject.

But in other cases, it has other forms, for example:

• bez čtyř sazenic = without four seedlings
• ke čtyřem sazenicím = toward four seedlings
• se čtyřmi sazenicemi = with four seedlings

So čtyři is not fixed; it declines.

A few useful pronunciation points:

• Czech stress is usually on the first syllable:

  • ČTYři
  • SAzenice
  • JSOU
  • ZAhonu
• č sounds like ch in church.
• c sounds like ts.
• j sounds like English y.
• ř in čtyři is the famous Czech sound; for beginners, an approximate r/zh-like sound is a reasonable first step.

Rough learner-friendly approximations:

• čtyři ≈ chti-rzhi
• sazenice ≈ sa-ze-ni-tse
• jsou ≈ careful speech y-sou, often closer to sou in casual speech
• záhonu ≈ zaa-ho-nu

The most important thing at first is to get the first-syllable stress and the clear consonants.