Los restos vegetales llenan el compostador.

In Spanish, it is very common to use the definite article with general, identifiable things. Los restos vegetales means the plant scraps / the vegetable matter / the organic plant remains in a general or contextual sense.

Here, los tells us we are talking about a specific class of material, or the scraps being discussed in the situation. Spanish often uses articles where English may leave them out.

For example:

• Los perros son animales fieles = Dogs are loyal animals
• Los restos vegetales llenan el compostador = Plant scraps fill the composter

So the article sounds natural here.

In Spanish, adjectives usually come after the noun they describe.

So:

• restos vegetales = plant remains / vegetable scraps

This is the normal pattern:

• casa grande = big house
• material orgánico = organic material
• restos vegetales = plant scraps

Putting the adjective after the noun is the standard, neutral order.

Because restos is plural, the adjective must agree with it in number.

• singular: resto vegetal
• plural: restos vegetales

This is basic adjective agreement in Spanish:

• libro interesante → libros interesantes
• resto vegetal → restos vegetales

Both the noun and adjective are masculine plural here.

Because restos usually refers to bits, remains, scraps, leftovers, which are naturally thought of as multiple pieces rather than one single item.

So:

• un resto = a remainder / a remnant
• los restos = the remains / the scraps

In composting or gardening contexts, Spanish commonly uses the plural because you are talking about many bits of organic matter.

It usually means plant remains, plant scraps, vegetable matter, or organic plant waste, depending on context.

In a composting context, it could include things like:

• leaves
• grass cuttings
• fruit and vegetable peelings
• small branches
• dead plant material

So it does not only mean edible vegetables. Vegetal here relates to plants in general.

Llenan is the 3rd person plural present tense of llenar (to fill).

The subject is los restos vegetales, which is plural, so the verb must also be plural:

• el resto llena = the scrap/remains fill
• los restos llenan = the scraps/remains fill

That is why we get:

• Los restos vegetales llenan el compostador

Because llena would be singular, and the subject here is plural.

Compare:

• El resto vegetal llena el compostador = The plant scrap fills the composter
• Los restos vegetales llenan el compostador = The plant scraps fill the composter

The ending -an shows that the verb matches a they subject.

No. Llenar is normally a direct transitive verb, so it takes a direct object without a preposition.

Pattern:

• algo llena algo
• something fills something

So:

• Los restos vegetales llenan el compostador

There is no a here because el compostador is the direct object, and it is a thing, not a person.

You may also see:

• llenar de = to fill with
  • Llenan el compostador de restos vegetales = They fill the composter with plant scraps

That is a slightly different structure.

Because the personal a is mainly used before specific people (and sometimes pets or personified beings), not ordinary objects.

So:

• Veo a María
• Conozco a tu hermano

But:

• Llenan el compostador
• Abro la puerta
• Limpio la cocina

Since el compostador is a thing, there is no a.

Yes, both kinds of words exist, depending on region and usage.

In Spain, compostador is a common word for a composter / compost bin / compost container.
You may also hear:

• compostera
• contenedor de compost
• compostador doméstico

Word choice can vary by country and even by context. In this sentence, el compostador is perfectly natural in Peninsular Spanish.

Yes, grammatically you can, but it means something slightly different.

• llenan = simple present
  This can express a general fact, a habitual action, or a present situation in a broad way.
• están llenando = present progressive
  This emphasizes the action as happening right now, in progress.

So:

• Los restos vegetales llenan el compostador = neutral statement / general description
• Los restos vegetales están llenando el compostador = the plant scraps are filling the composter right now

In many cases, Spanish uses the simple present where English might prefer are filling.

The given order is the most neutral and natural:

• Los restos vegetales llenan el compostador

Spanish word order is flexible, but changing it usually changes the emphasis.

For example:

• El compostador lo llenan los restos vegetales
  This puts more focus on the composter
• Llenan el compostador los restos vegetales
  This can sound more literary or marked

For everyday neutral Spanish, the original order is best.

There are two main clues:

1. Verb agreement
   The verb is llenan, which is plural, so it agrees with los restos vegetales, the plural noun phrase.

2. Meaning and structure
   With llenar, the thing doing the filling is the subject, and the thing being filled is the direct object:

   • X llena Y = X fills Y

So here:

• los restos vegetales = subject
• el compostador = direct object

Not exactly in this sentence. Here vegetales is best understood as plant-related or of plant origin, not specifically vegetables you eat.

That is why restos vegetales often means:

• plant waste
• garden waste
• plant remains
• organic matter from plants

If you specifically wanted vegetable scraps from food, context would usually make that clear, and Spanish might also use expressions like:

• restos de verduras
• sobras de verduras
• desechos vegetales

But in composting language, restos vegetales is broad and natural.

In most of Spain, ll is pronounced like y in modern standard speech, so llenan sounds roughly like YE-nan.

Very roughly:

• llenan ≈ YEH-nan

A few pronunciation notes:

• ll and y are pronounced the same in most of the Spanish-speaking world
• the e is a clear short vowel, like eh
• the stress is on the first syllable: LLE-nan

So the whole sentence is approximately:

• los RES-tos ve-he-TA-les YE-nan el com-pos-ta-DOR

In much of Spain, g before e in vegetales sounds like a soft throaty sound, not like English j.