Once you have mastered the basic elements of English grammar, it will be relatively easy to learn other aspects of English grammar, as they flow on from each other. One of the aspects you should learn is adverb clauses, and how they are used.
An adverb clause is a subordinate clause that modifies a verb, an adjective or another adverb. It tells when, where, how, to what extent or under what conditions.
One example of an adverb clause is as follows: Before winter began, I planted bulbs. The adverb clause "before winter began" tells when and modifies the verb planted. Another example: Bulbs usually do well if you use fertilizer. The adverb clause "if you use fertilizer" tells under what conditions and modifies the adverb well.
For the example "The flowers are beautiful because the winter was mild," the adverb clause "because the winter was mild" tells why and modifies the adjective "beautiful." In the colloquial speech of most cultures, words tend to be omitted when they are easily inserted or understood.
Elliptical adverb clauses have words left out of them. You can easily supply the omitted words because they are understood or implied. For example: "The hyacinths are more fragrant than the tulips [are fragrant]." Another example: "While [I am] gardening, I always take time to enjoy the flowers."