In horto rosae et lilia florent, et avia dicit hortum hodie pulchriorem esse quam heri.

Because in takes the ablative when it means in or inside, showing location.

• in horto = in the garden
• If in showed motion into something, it would take the accusative instead.

So this is the normal place where construction.

Latin has no articles, so it does not have separate words for the or a/an.

That means horto can mean:

• garden
• the garden
• a garden

You decide from context which English wording is most natural.

Because of its job in the sentence.

In rosae et lilia florent, the words rosae et lilia are the subject of florent. Since florent is plural, rosae must be nominative plural here: roses.

The form rosae can also be genitive singular or dative singular in other contexts, but here the syntax makes the meaning clear.

Because lilia is a neuter plural form from lilium.

For many second-declension neuter nouns:

• singular nominative: -um
• plural nominative: -a

So:

• lilium = lily
• lilia = lilies

This is very common in Latin. Neuter plurals often end in -a.

Florent is the 3rd person plural present active form of florere, meaning to bloom or to flower.

It is plural because the subject is plural:

• rosae et lilia = roses and lilies
• therefore florent = they are blooming

Also, the verb is from the 2nd conjugation, so the plural ending here is -ent.

Avia is the subject of dicit.

So the structure is:

• avia dicit = grandmother says

It is nominative singular because it is the one doing the speaking.

Because Latin very often uses an accusative-and-infinitive construction after verbs of saying, thinking, knowing, hearing, and so on.

Instead of using a clause like:

• grandmother says that the garden is prettier

Latin commonly says:

• grandmother says the garden to be prettier

That sounds strange in English, but it is normal Latin.

So:

• dicit = says
• hortum ... esse = that the garden is ...

Because it is the subject of the infinitive esse inside the indirect statement.

In the accusative-and-infinitive construction:

• the subject of the infinitive goes into the accusative
• the infinitive stays in infinitive form

So:

• avia dicit
• hortum pulchriorem esse

literally means something like:

• grandmother says the garden to be prettier

That is why it is hortum, not hortus.

Because it agrees with hortum.

Inside the indirect statement:

• hortum = accusative singular masculine
• pulchriorem = accusative singular masculine comparative adjective

It is the comparative form of pulcher, meaning beautiful.

Basic comparison:

• pulcher = beautiful
• pulchrior = more beautiful / prettier
• pulchriorem = accusative singular of that comparative form

Since it describes hortum, it must match it in gender, number, and case.

Because Latin normally keeps the infinitive esse in this kind of indirect statement.

English often allows us to say:

• she says the garden is prettier

Latin uses:

• dicit hortum pulchriorem esse

So esse is not optional here in normal classical prose. It completes the accusative-and-infinitive construction.

This is a normal comparison with an understood verb.

• pulchriorem ... quam heri = prettier ... than yesterday

More fully, the idea is:

• prettier than it was yesterday

Latin often leaves out repeated words when they are easy to understand. This is called ellipsis.

Also, heri is an adverb meaning yesterday, not a noun in some case ending.

They are both adverbs of time.

• hodie = today
• heri = yesterday

They do not change form for case, number, or gender.

In this sentence:

• hodie tells you when the garden is prettier
• heri gives the point of comparison

Yes, but in a normal Latin way. Latin word order is more flexible than English word order because endings show the grammatical relationships.

This sentence is arranged for flow and emphasis:

• In horto comes first to set the scene
• rosae et lilia florent gives the main picture
• avia dicit introduces the second clause
• hortum hodie pulchriorem esse quam heri saves the comparison for the end

A more rigid English-style order is not necessary in Latin, because forms like hortum and pulchriorem already show how the words function.