El perejil crece en la sombra parcial.

In Spanish, it is very common to use the definite article with a noun when talking about something in general.

So El perejil crece... means Parsley grows... as a general fact.

English often drops the article in this kind of sentence, but Spanish usually keeps it:

• El arroz es básico en muchas cocinas.
• La menta crece rápido.

Also, perejil is a masculine singular noun, so the article is el.

Crece is the third-person singular present form of crecer.

The subject is el perejil, which is grammatically singular, so the verb must also be singular:

• crecer = to grow
• el perejil crece = parsley grows

A quick conjugation of crecer in the present:

• yo crezco
• tú creces
• él / ella / usted crece
• nosotros crecemos
• ellos / ellas / ustedes crecen

Notice that only yo has the spelling change crezco.

Here, crece most naturally means grows in a general sense.

Spanish uses the simple present for things like:

• general truths
• habits
• typical characteristics

So El perejil crece en la sombra parcial means something like Parsley grows in partial shade or Parsley does well in partial shade.

If you wanted to emphasize that it is happening right now, Spanish would more likely use:

• está creciendo

So:

• El perejil crece... = general fact
• El perejil está creciendo... = it is growing right now

En is the normal preposition for location or environment, and here it means something like in or under that condition.

So:

• en la sombra parcial = in partial shade / under partial shade conditions

Spanish often uses en for the place or conditions where something happens:

• crece en climas cálidos
• vive en el campo
• florece en primavera

Because sombra parcial is a noun phrase, and here it is being presented as the condition of partial shade.

Spanish often uses articles in places where English might leave them out.

So even though English says in partial shade, Spanish may use an article:

• en la sombra parcial

That said, in real gardening Spanish, you may also hear slightly different wording, depending on the region.

In Spanish, most descriptive adjectives come after the noun.

So:

• sombra parcial = partial shade
• clima cálido = warm climate
• luz directa = direct light

This is the normal word order in Spanish.

If you put the adjective before the noun, it often sounds literary, unusual, or changes the nuance. In this sentence, sombra parcial is the standard order.

It is understandable, but it may not be the most natural gardening phrase everywhere.

Depending on the region, people may also say:

• semisombra
• sombra parcial
• sometimes media sombra, depending on context and country

So a more natural version in many situations might be:

• El perejil crece en semisombra.

That does not mean your original sentence is wrong. It just means there may be a more idiomatic gardening term depending on where the Spanish is being used.

Yes. It is singular, but Spanish often uses the singular form to talk about something as a category or substance in general.

So:

• El perejil = parsley, as a plant/type of herb in general

This is similar to:

• El café se cultiva en muchas regiones.
• La manzana es nutritiva.

Spanish could also use the plural in some contexts, but the singular with the article is very common for general statements like this.

A simple Latin American-style guide:

• perejil ≈ peh-reh-HEEL
• crece ≈ KREH-seh

A few details:

• In perejil, the stress is on the last syllable: -jil
• The j sounds like a strong English h, but rougher
• In most of Latin America, the c in crece before e sounds like s

So:

• crece sounds like KREH-seh, not KREH-keh

Yes, grammatically you could, but it changes the meaning.

• El perejil crece en la sombra parcial = parsley grows in partial shade; a general fact
• El perejil está creciendo en la sombra parcial = the parsley is growing in partial shade right now

So the original sentence is better if you are stating a general gardening fact. The estar + gerundio form is better for a specific ongoing situation.