Без удобрения орхидея растёт медленнее, а кактус почти не меняется.

Because без (without) requires the genitive in Russian.

• без удобрения = without fertilizer
• Dictionary form: удобрение
• Genitive singular: удобрения

This is a fixed case pattern you need to learn with the preposition:

• без сахара = without sugar
• без воды = without water
• без удобрения = without fertilizer

So the form удобрения is there because of без, not because it is the subject.

Here удобрение is being used as an uncountable substance/material noun, so singular is natural.

• без удобрения = without fertilizer / without any fertilizer

Using the plural без удобрений would suggest without fertilizers in the sense of different kinds or products, which is possible in some contexts, but it is less neutral here.

So in this sentence, singular sounds like the normal general statement.

Both are in the nominative case because they are the subjects of their clauses.

• орхидея растёт медленнее = the orchid grows more slowly
• кактус почти не меняется = the cactus hardly changes

So:

• орхидея = nominative singular
• кактус = nominative singular

Растёт is the 3rd person singular present tense of расти (to grow).

Because the subject is singular:

• орхидея растёт = the orchid grows

If the subject were plural:

• орхидеи растут = orchids grow

Also note the spelling with ё:

• растёт

In many texts, ё is often written as е: растет, but the pronunciation is still rastYOT.

Медленнее is the normal comparative form of медленно (slowly).

• медленно = slowly
• медленнее = more slowly

So:

• орхидея растёт медленнее = the orchid grows more slowly

Russian often prefers this simple comparative form over более + adverb/adjective.

Both can exist in Russian, but медленнее is the more natural choice here.

Russian comparatives often do not need an explicit than-phrase if the comparison is understood from context.

So растёт медленнее can mean:

• grows more slowly
• grows more slowly than before
• grows more slowly than under normal conditions
• grows more slowly than when fertilized

In this sentence, без удобрения gives the comparison context, so the meaning is clear without saying чем... (than...).

А is often used to contrast or set two things against each other.

Here the sentence compares two plants:

• орхидея растёт медленнее
• кактус почти не меняется

So а works well because the behavior of the orchid and the cactus is being contrasted.

Compare:

• и = and, simple addition
• а = and/but, with contrast
• но = but, stronger contradiction

In this sentence, а is the most natural connector.

Because this is a compound sentence with two clauses, each with its own subject and verb:

1. Без удобрения орхидея растёт медленнее
2. а кактус почти не меняется

Russian normally puts a comma before а when it joins two clauses like this.

Literally, it means almost does not change.

Breakdown:

• почти = almost
• не = not
• меняется = changes / is changing

So:

• почти не меняется = hardly changes / almost doesn’t change

This is a very common Russian pattern:

• почти не спит = hardly sleeps
• почти не ест = hardly eats
• почти не работает = barely works

Because почти не is the standard combination meaning almost not or more naturally hardly.

• почти не меняется = hardly changes

Putting не before почти would sound wrong in normal Russian for this meaning.

So you should learn почти не + verb as a common pattern.

The verb is меняться, which means to change in the sense of undergo change.

• менять = to change something
• меняться = to change oneself / to change / to undergo change

So:

• Он меняет план. = He changes the plan.
• План меняется. = The plan changes.

Here:

• кактус почти не меняется = the cactus hardly changes

The cactus is not changing something else; it is itself undergoing little change.

Yes, Russian word order is fairly flexible, though different orders change the emphasis.

The sentence as given:

• Без удобрения орхидея растёт медленнее, а кактус почти не меняется.

This is neutral and natural.

You could also say:

• Орхидея без удобрения растёт медленнее, а кактус почти не меняется.

That still works, but it places орхидея a little more prominently.

Russian word order often reflects focus and information structure, not just grammar. The original version sounds smooth and natural for a general statement.

In normal reading, без удобрения applies to the whole comparison, so to both plants.

The idea is:

• without fertilizer, the orchid grows more slowly
• while the cactus hardly changes

Russian often places a phrase like без удобрения at the beginning when it sets the condition for everything that follows.

If you wanted to make it apply only to the orchid, you would usually need clearer wording or a different structure.

Yes. In this context, удобрение most naturally means fertilizer.

It is a broad word and can refer to plant nutrients in general, not just one specific product.

Depending on context, it can also mean plant feed, fertilizing agent, or similar, but fertilizer is the best basic translation here.

Russian has no articles. So nouns like орхидея and кактус can mean:

• an orchid / the orchid
• a cactus / the cactus

The exact meaning depends on context.

In this sentence, English often uses the orchid and the cactus because we are talking about specific representative plants in a comparison, but Russian does not mark that difference with articles.