Весной мама добавляет удобрение в почву, чтобы растения росли быстрее.

Yes. Весной means in spring / during spring.

It is the instrumental singular form of весна (spring), but in Russian the instrumental is often used in fixed time expressions like this:

• весной — in spring
• летом — in summer
• осенью — in autumn
• зимой — in winter

So in this sentence, Весной works like a time adverb.

Russian often uses the present tense to describe habitual or repeated actions.

So мама добавляет means:

• Mom adds
• Mom is in the habit of adding
• Mom adds every spring

It does not have to mean she is doing it right now. It can describe a general routine.

Добавляет is from the imperfective verb добавлять. The imperfective is used here because the sentence describes a habitual / repeated action, not a single completed event.

Compare:

• Мама добавляет удобрение... — Mom adds fertilizer... / Mom regularly adds fertilizer...
• Мама добавит удобрение... — Mom will add fertilizer... (one future completed action)

So the imperfective fits the idea of something done as part of a recurring practice.

Yes. Удобрение here is being used as a mass/general noun, like fertilizer in English.

So it means something like:

• fertilizer
• some fertilizer
• fertilizer in general

Russian often uses the singular this way. If you used the plural удобрения, it could suggest:

• different kinds of fertilizers
• multiple fertilizer products
• fertilizers in a more countable sense

Because в почву shows direction into something, so it takes the accusative case.

Here the idea is:

• Mom adds fertilizer into the soil

Compare:

• в почву — into the soil / motion toward the inside
• в почве — in the soil / location

So:

• добавляет удобрение в почву = adds fertilizer into the soil
• удобрение в почве = fertilizer is in the soil

Почву is the accusative singular form of почва (soil).

Since в can take different cases depending on meaning, here it takes the accusative because there is movement/direction:

• почва — nominative
• в почву — into the soil

This is a very common pattern in Russian:

• в дом — into the house
• в городе — in the city
• на стол — onto the table
• на столе — on the table

Чтобы introduces a purpose clause. Here it means:

• so that
• in order that
• so

So the sentence structure is:

• Мама добавляет удобрение в почву, чтобы растения росли быстрее.
• Mom adds fertilizer to the soil so that the plants grow faster.

It explains why she adds the fertilizer.

This is one of the most common learner questions.

Yes, росли looks like a past tense plural form, and historically it is that form. But after чтобы, Russian often uses this form to express a desired, intended, or hypothetical result.

So:

• чтобы растения росли быстрее = so that the plants would grow faster / so that the plants grow faster

It is not ordinary past meaning here.

Why росли?

• растения is plural
• so the verb is plural: росли

This pattern is very common:

• Я учусь, чтобы лучше говорить по-русски. — I study so that I can speak Russian better.
• Мы открыли окно, чтобы было прохладнее. — We opened the window so that it would be cooler.

So after чтобы, the -л form often expresses purpose or desired outcome rather than simple past time.

Usually, after чтобы, the particle бы is already built into чтобы, so you normally do not need another бы.

So:

• чтобы растения росли быстрее — normal
• чтобы растения росли бы быстрее — generally unnecessary and usually avoided in standard usage

In most purpose clauses, чтобы already carries that function by itself.

Быстрее is the comparative form of быстро and means faster.

So:

• быстро — quickly / fast
• быстрее — faster / more quickly

Here the idea is not just that the plants grow quickly, but that they grow faster than they otherwise would.

Here it functions as an adverb, because it describes how the plants grow.

It is connected to the verb:

• росли быстрее — grew / would grow faster

Compare:

• быстрые растения — fast plants (adjective)
• растения росли быстрее — the plants grew faster (adverb)

Russian word order is flexible, and putting Весной first highlights the time.

So this order sounds natural and may emphasize in spring as the setting:

• Весной мама добавляет удобрение в почву...

Other orders are also possible:

• Мама весной добавляет удобрение в почву...
• Мама добавляет удобрение в почву весной...

The basic meaning stays the same, but the emphasis shifts a little. Starting with Весной makes the time frame feel especially prominent.

Both can relate to earth/soil, but почва is more specifically soil, especially as a growing medium for plants.

• почва — soil
• земля — earth, land, ground, soil, dirt

In a gardening or plant-growth context, почва is often the more precise word. So в почву sounds very natural when talking about adding fertilizer for plants.

Yes. The structure with чтобы makes the purpose very clear.

The sentence is not just saying:

• Mom adds fertilizer to the soil.

It specifically says she does it for a reason:

• so that the plants grow faster

So the second half explains the intended benefit of the first half.