Ni nutras la planton per sterko.

Because la planton is the direct object of the verb nutras.

In Esperanto, direct objects normally take the ending -n. So:

• planto = plant
• planton = plant, as the thing being acted on

Here, we are doing the action of feeding, and the plant is receiving that action, so it becomes la planton.

The ending -as marks the present tense in Esperanto.

So:

• nutri = to feed / to nourish
• nutras = feed / are feeding / nourish / are nourishing

In this sentence, Ni nutras la planton per sterko means that we feed/nourish the plant with fertilizer/manure in the present tense.

La is the definite article, meaning the.

So la planton means the plant.

Esperanto has only one article, la, and it does not change for gender, number, or case. Even though planton has -n, the article stays la.

Because sterko is being used in a general or material sense: with manure/fertilizer.

In Esperanto, you often leave out la when talking about a substance or material in a general way.

So:

• per sterko = with fertilizer / with manure
• per la sterko would mean with the fertilizer, referring to some specific fertilizer already known in the conversation

Per means by means of, with, or using.

It shows the method, instrument, or means used to do something.

So in this sentence:

• Ni nutras la planton per sterko = We feed the plant by means of fertilizer/manure

This is different from simply saying with in the sense of accompanying someone. For that, Esperanto often uses kun.

So:

• per sterko = using fertilizer
• kun sterko would sound more like being together with fertilizer, not using it as the means

Yes, Esperanto word order is fairly flexible, because endings show the grammatical roles.

The most neutral order is:

• Ni nutras la planton per sterko.

But other orders are possible, such as:

• La planton ni nutras per sterko.
• Per sterko ni nutras la planton.

These can change the emphasis, but the meaning stays basically the same because planton still has -n, marking it as the direct object.

Yes, nutri can be used for plants too. It means to nourish or to feed, not only in the everyday animal sense but also more generally.

So this sentence is natural if you mean that the plant is being nourished by fertilizer.

Depending on context, someone might also express a similar idea in other ways, but nutri is perfectly understandable here.

Sterko usually means manure or fertilizer, depending on context.

In a gardening sentence like this, English might translate it as:

• manure
• fertilizer
• sometimes more broadly plant food

If the context is farming or traditional agriculture, sterko may strongly suggest manure. In a more general gardening context, fertilizer is often a good translation.

In Esperanto, the subject is usually stated clearly, and verbs do not change depending on the person.

So:

• mi nutras
• vi nutras
• ni nutras
• ili nutras

All use nutras.

Because the verb form does not show who is doing the action, Esperanto normally keeps the subject pronoun unless the subject is already obvious from context.

So ni is needed here to mean we.

Yes. Esperanto -as covers the general present tense.

So nutras can correspond to English:

• feed
• are feeding
• nourish
• are nourishing

The exact English translation depends on context. Esperanto does not force the same distinction that English often makes between simple present and present progressive.

The plural ending in Esperanto is -j.

So:

• planto = plant
• plantoj = plants

If it is also the direct object, you add -n as well:

• la plantojn = the plants

So the full sentence would become:

• Ni nutras la plantojn per sterko. = We feed the plants with fertilizer/manure.

Because sterko is not the direct object. It is part of a prepositional phrase introduced by per.

In Esperanto, prepositions like per, kun, en, sur, and so on normally take a noun without -n.

So:

• la planton gets -n because it is the direct object
• per sterko does not get -n because sterko is governed by the preposition per

That is why the sentence is:

• Ni nutras la planton per sterko.