El sistema de raíces crece en el sustrato para macetas.

Because the grammatical subject is El sistema de raíces, and the head of that subject is sistema, which is singular. The phrase de raíces just explains what kind of system it is.

So Spanish is agreeing with sistema, not with raíces.

• El sistema ... crece
• not Las raíces ... crecen

If the subject were Las raíces, then the verb would be plural: Las raíces crecen...

Both are possible, but they are not exactly the same in tone.

• El sistema de raíces sounds more technical, scientific, or botanical.
• Las raíces sounds more everyday and simpler.

So this sentence has a slightly formal or specialized feel. In a gardening or biology context, sistema de raíces is very natural.

Because nouns ending in -z change z to c before -es in the plural.

So:

• raíz → raíces
• luz → luces
• pez → peces

This spelling change keeps the pronunciation natural in Spanish.

The accent is there because raíz and raíces contain a stressed í that forms a hiatus rather than blending into a single syllable with the a.

So it is pronounced like:

• ra-ÍZ
• ra-Í-ces

The accent helps show that the í is stressed.

In this sentence, sustrato means the material or growing medium that plants grow in. In gardening, it often refers to things like potting mix, planting medium, or substrate.

It is more specific than plain soil in some contexts. Sustrato is common in horticulture, botany, and agriculture.

Because sustrato is a more technical gardening word.

Very roughly:

• tierra often means earth, dirt, or soil in a general sense
• suelo often means ground, floor, or soil in a broader/environmental sense
• sustrato means a growing medium, especially one prepared for plants

For potted plants, sustrato is often the best word, especially in Latin American gardening contexts.

Para macetas means the substrate is intended for pots or for use in pots. The preposition para expresses purpose or intended use.

So sustrato para macetas is basically potting substrate / potting mix / substrate for pots.

If you changed para, the meaning would shift.

It is plural because it refers to pots in a general sense, not to one specific pot.

There is no article because after para, Spanish often leaves nouns bare when speaking generically about purpose or use.

So:

• sustrato para macetas = substrate intended for pots in general

This is similar to how Spanish often says things like:

• agua para plantas
• bolsa para basura
• comida para perros

Both are possible, but they mean slightly different things.

• el sustrato can refer to the substrate in a general/class sense or to a specific substrate already understood from context
• un sustrato would introduce one substrate or one type of substrate

So en el sustrato para macetas sounds like in the potting substrate / in the potting mix, either as a known material or as a general category.

Because en is the normal preposition for something growing in a material or environment.

Roots grow en el sustrato, just as a plant can grow:

• en la tierra
• en agua
• en una maceta

Here en means the root system is developing within that growing medium.

Yes. Crecer is completely natural for plants, roots, stems, and living things in general.

You can say:

• La planta crece
• Las raíces crecen
• El sistema de raíces crece

In scientific or gardening language, this is normal and idiomatic.

Yes. Sistema radicular is a very natural botanical term and is often even more technical than sistema de raíces.

The difference in tone is roughly:

• sistema de raíces = clear, descriptive, technical
• sistema radicular = more specialized/scientific

Both are correct.

It sounds somewhat technical because of sistema de raíces and sustrato. It is perfectly natural in gardening, botany, agriculture, or educational writing.

In more casual speech, someone might simplify it to something like:

• Las raíces crecen en la tierra de la maceta
• Las raíces crecen en el sustrato de la maceta

So the original sentence is correct, but it has a more formal or specialized feel.

Sometimes, but it changes the nuance.

• sustrato para macetas = substrate intended for use in pots
• sustrato de maceta = substrate of a pot, or substrate associated with a pot

If you are talking about a commercial growing medium or a general type of mix, para macetas is usually the better choice. It sounds like a product or category meant for potted plants.