Pon el tarro de miel en la balda de abajo, que pesa mucho.

Pon is the tú imperative of poner: poner → pon.

It’s used when giving a direct instruction to one person in an informal way, like Put... in English.

• Pon el tarro... = Put the jar...
• Pone is usually he/she/it puts or you put (usted) in the present tense, not the informal command.

Related forms:

• pon = command to tú
• ponga = command to usted
• poned = command to vosotros (common in Spain)
• pongan = command to ustedes

In Spanish, de + noun is very commonly used to show content, type, or material.

So:

• tarro de miel = jar of honey
• vaso de agua = glass of water
• taza de café = cup of coffee

You usually don’t use the article here unless you mean a specific, already identified honey:

• el tarro de miel = a jar of honey / the honey jar
• el tarro de la miel = the jar of the honey we already mentioned

So tarro de miel is the normal choice.

Tarro means jar.

In this sentence, it suggests a container like the kind honey often comes in. In Spain, tarro is a very natural word here.

Similar words include:

• frasco = jar / bottle, often a bit more “container-like” or glass-container-like
• bote = container / jar / tub, depending on context

For honey, tarro sounds very normal.

Balda means shelf, especially one individual shelf inside a cupboard, cabinet, or bookcase.

In Spain, balda is a very common word for the actual shelf level or board you put things on.

Estante can also mean shelf, but depending on context it can refer more generally to shelving or a shelving unit. So in this sentence, balda is very precise: it means the shelf where you should place the jar.

De abajo means the one below or the lower one.

So:

• la balda de abajo = the lower shelf / the shelf below

This is a very common Spanish pattern:

• el cajón de arriba = the top drawer
• la habitación de al lado = the room next door
• la puerta de enfrente = the door opposite

You usually need de when this kind of location phrase describes a noun.

Just abajo on its own is an adverb meaning down / below, so it works differently:

• Pon el tarro abajo = Put the jar down / below

But la balda de abajo specifically identifies which shelf.

Here, que is most naturally understood as a causal connector, meaning something like because or since.

So the sentence is basically:

• Pon el tarro de miel en la balda de abajo, que pesa mucho.
• Put the jar of honey on the lower shelf, because it weighs a lot.

This use of que is very common in spoken Spanish, especially in Spain, after a pause or comma.

Compare:

• Vete, que es tarde. = Go on, it’s late.
• Abrigaos, que hace frío. = Wrap up, it’s cold.

So this que is not necessarily just that.

In terms of meaning, it almost certainly refers to the jar.

However, this is exactly the kind of thing learners often notice, because grammatically it can look a bit ambiguous.

Why? Because que can also introduce a relative clause:

• la balda de abajo, que pesa mucho
  literally looks like the lower shelf, which weighs a lot

That doesn’t make much sense in normal context, so real-life meaning pushes you toward understanding the jar as the thing that is heavy.

To make it completely clear, Spanish could say:

• Pon el tarro de miel en la balda de abajo porque pesa mucho.
• Como el tarro de miel pesa mucho, ponlo en la balda de abajo.
• Pon el tarro de miel en la balda de abajo, porque el tarro pesa mucho.

So the original sentence is understandable, but it has a bit of structural ambiguity.

Because Spanish often omits subject pronouns and repeated subjects when they are understood from context.

So pesa mucho can mean:

• it weighs a lot
• he/she weighs a lot
• the jar weighs a lot

In this sentence, Spanish doesn’t need to repeat el tarro if the speaker thinks it’s obvious.

This is very normal in Spanish:

• Está cansado. = He’s tired.
• No vienen. = They aren’t coming.
• Pesa mucho. = It weighs a lot.

Here mucho means a lot.

It’s working as an adverb with the verb pesar:

• pesa mucho = it weighs a lot

English often uses very with adjectives:

• It’s very heavy

Spanish can also say that:

• es muy pesado

So these are both natural, but they are structured differently:

• pesa mucho = it weighs a lot
• es muy pesado = it is very heavy

The comma helps show that the final part is an added explanation.

So the rhythm is:

• Pon el tarro de miel en la balda de abajo, que pesa mucho.

That pause makes que pesa mucho sound like an extra reason or comment.

If you removed the comma, the sentence would more strongly look like que pesa mucho is directly describing la balda:

• la balda de abajo que pesa mucho = the lower shelf that weighs a lot

That reading is probably not what is meant, so the comma matters.

The rest of the sentence would stay basically the same, but the command form of poner would change.

• Pon el tarro... = informal singular (tú)
• Ponga el tarro... = formal singular (usted)
• Poned el tarro... = informal plural in Spain (vosotros)
• Pongan el tarro... = formal plural / standard plural outside Spain (ustedes)

So you could have:

• Ponga el tarro de miel en la balda de abajo, que pesa mucho.
• Poned el tarro de miel en la balda de abajo, que pesa mucho.
• Pongan el tarro de miel en la balda de abajo, que pesa mucho.