Mi madre pone romero y tomillo en el pollo cuando lo cocina en el horno.

Pone is the 3rd person singular present form of poner.

• poner = to put, to place, to add
• pone = he/she puts, he/she adds

So mi madre pone... means my mother puts/adds...

A quick conjugation:

• yo pongo
• tú pones
• él/ella pone
• nosotros ponemos
• vosotros ponéis
• ellos ponen

In normal Spanish, you usually use a possessive adjective before the noun:

• mi madre = my mother

Madre mía is not the normal neutral way to say my mother in a sentence like this. It is usually:

• an exclamation: ¡Madre mía!
• or a more emotional/literary structure

La mi madre is not standard everyday modern Spanish in most contexts.

So mi madre is the natural choice here.

Because Spanish often omits the article with ingredients or substances when speaking in a general way.

So:

• pone romero y tomillo = she adds rosemary and thyme

This sounds like general seasoning.

If you said pone el romero y el tomillo, it would sound more like:

• specific rosemary and thyme already known in the conversation
• or a more marked, contrastive style

In recipe-like language, leaving out the article is very common.

En el pollo focuses on the idea of putting the herbs on/into the chicken.

In cooking Spanish, this is understandable and natural. But another very common structure is:

• Mi madre le pone romero y tomillo al pollo

That version means essentially the same thing:

• le pone X al pollo = she adds X to the chicken

So:

• en el pollo = on/in the chicken
• al pollo with ponerle = to the chicken

Both are possible, but they are built differently.

Lo is a direct object pronoun that refers back to el pollo.

So instead of repeating:

• cuando cocina el pollo

the sentence says:

• cuando lo cocina

That is very normal in Spanish. It avoids repetition and sounds smoother.

Here:

• lo = el pollo

Because el pollo is the direct object of cocina.

• cocinar algo = to cook something

So the correct standard direct object pronoun is:

• lo for a masculine singular thing

Examples:

• Cocina el pollo → Lo cocina
• Cocina la carne → La cocina

Le is normally for indirect objects in standard Spanish.

In some parts of Spain, you may hear le for masculine people (leísmo), but that does not apply here.

Because this sentence describes a habitual action, not a future one-time event.

With cuando, Spanish uses:

• indicative for habitual or repeated actions

  • cuando lo cocina = whenever she cooks it

• subjunctive for future or not-yet-realized actions

  • cuando lo cocine mañana = when she cooks it tomorrow

So here, cuando lo cocina is correct because it means whenever she cooks it in the oven.

Because Spanish, like English, uses the simple present to talk about habits or things someone usually does.

So this sentence is not necessarily about what she is doing right now. It means something like:

• this is her usual way of cooking chicken
• she generally does this

That is why pone and cocina are both in the present tense.

Spanish usually keeps the definite article with common places and objects where English often does not.

So Spanish says:

• en el horno = in the oven
• en la cocina = in the kitchen
• en el coche = in the car

Leaving out el here would sound incomplete or unnatural in standard Spanish.

Spanish cocinar is a broad verb meaning to cook.

When you add en el horno, the idea becomes:

• cook in the oven
• bake
• roast

The exact English translation depends on context. For pollo, English might naturally say:

• bakes the chicken
• roasts the chicken
• cooks the chicken in the oven

Spanish does not have to choose one very specific verb here.

Yes, Spanish word order is fairly flexible, though some orders sound more neutral than others.

The original sentence is natural and clear:

• Mi madre pone romero y tomillo en el pollo cuando lo cocina en el horno.

You could also say:

• Cuando cocina el pollo en el horno, mi madre pone romero y tomillo en el pollo.

But one thing does stay important: object pronouns like lo usually go before the conjugated verb:

• cuando lo cocina
• not cuando cocina lo

So the overall order can move, but lo still needs to be in the right place.