Konev je plná dešťové vody, což pomůže zalévat sazenice.

Because konev is a feminine noun in Czech, so the adjective has to agree with it.

• konev = watering can
• feminine singular noun
• adjective must match: plná = full

Compare:

• hrnek je plný = the mug is full (hrnek is masculine)
• láhev je plná = the bottle is full (láhev is feminine)

So Konev je plná... means the adjective is correctly agreeing with a feminine singular subject.

Because after plný / plná / plné in Czech, the thing something is full of is usually put in the genitive.

So:

• plná vody = full of water
• not plná vodu

In this sentence:

• voda = water
• genitive singular: vody
• adjective dešťová also changes to genitive singular feminine: dešťové

So:

• dešťová voda = rainwater
• plná dešťové vody = full of rainwater

This is a very common pattern:

• sklenice je plná mléka = the glass is full of milk
• krabice je plná knih = the box is full of books

It literally means of rain water / of rainwater.

Grammatically:

• dešťová = rainy / rain-
• voda = water

Together, dešťová voda means rainwater. In the sentence it appears in the genitive because of plná, so it becomes dešťové vody.

So although English usually says just rainwater, Czech expresses it as an adjective + noun combination.

Což here means something like which, but it refers to the whole previous idea, not just one noun.

In this sentence:

• Konev je plná dešťové vody = The watering can is full of rainwater
• což pomůže zalévat sazenice = which will help water the seedlings

So což does not mean which watering can or which water. It means which fact / and that will help...

This is a very common use of což in Czech:

• it comments on the entire previous clause
• it is often translated as which, and that, or which in turn

Because což introduces a subordinate clause or comment clause, and in Czech those are normally separated by a comma.

So the structure is:

• main clause: Konev je plná dešťové vody
• following clause with což: což pomůže zalévat sazenice

Czech punctuation is stricter than English in this area. Even where English punctuation can sometimes feel flexible, Czech usually requires the comma.

Because pomůže is the present-tense form of a perfective verb, and in Czech perfective present forms usually express a future meaning.

Here:

• infinitive: pomoci = to help
• 3rd person singular: pomůže

Although it looks like a present form, it means:

• will help
• not is helping

This is very normal in Czech:

• udělá = he/she/it will do
• řekne = he/she/it will say
• pomůže = he/she/it will help

Because Czech often uses pomoci + infinitive to mean help to do something.

So:

• pomůže zalévat sazenice = it will help water the seedlings

This works much like English help do something.

You could also say something like:

• pomůže se zaléváním sazenic
• pomůže při zalévání sazenic

But pomůže zalévat sazenice is a straightforward and natural way to express will help water the seedlings.

This is about aspect.

• zalévat = imperfective
• zalít = perfective

The imperfective zalévat is used when talking about the activity in a general or ongoing sense: to water, to be watering, to water regularly.

In this sentence, the idea is that the rainwater will help with the activity of watering seedlings, so zalévat fits well.

If you used zalít, it would sound more like helping complete one whole watering event:

• pomůže zalít sazenice = it will help water the seedlings completely / as a single completed action

Both can be possible in some contexts, but zalévat is natural when the focus is the general practical use.

Here sazenice is the direct object of zalévat, so it is in the accusative.

The tricky part is that the form sazenice looks the same in several cases.

Most likely here it is:

• accusative plural = seedlings

So:

• zalévat sazenice = to water the seedlings

Czech learners often notice that some noun forms are identical across singular and plural or across different cases. This is one of those situations, so you understand the meaning from context.

Yes, in a normal neutral sentence like this, je is expected.

• Konev je plná dešťové vody = The watering can is full of rainwater

Czech does sometimes omit forms of být in certain informal styles, headlines, notes, or special constructions, but in an ordinary full sentence, je should be there.

So Konev plná dešťové vody by itself would sound incomplete unless it were being used as a caption, label, or fragment.

Yes, Czech word order is flexible, but the original order is the most neutral and natural here.

Neutral order:

• Konev je plná dešťové vody, což pomůže zalévat sazenice.

You could rearrange parts for emphasis, but then the sentence may sound more marked or literary. For example, Czech often moves information around to highlight what is new, important, or contrasted.

For a learner, the safest approach is:

• subject first
• then je
• then adjective phrase
• then the což clause

That gives a clear, standard sentence.

Yes, konev is feminine, even though it does not end in -a.

Czech gender is not determined only by the final letter. Many feminine nouns end in a consonant, especially nouns like:

• dlaň = palm
• píseň = song
• kázeň = discipline

And also nouns like konev.

That is why the adjective is feminine:

• ta konev
• plná konev would be wrong as a sentence fragment here, but the agreement feminine = plná is correct

So this sentence is also a good reminder that you often need to learn the gender together with the noun.