Definitions from Random House Dictionary (at Dictionary.com)
1. a feeling of discontent or covetousness with regard to another's advantages, success, possessions,
1. inordinately or wrongly desirous of wealth or possessions; greedy.
Envy is a feeling, which can be mild or violent, that is directed against another person's possession, advantages or successes and entails covetousness, which is a wrong or overly intense or misplaced strong desire for possessions or wealth. In Robert Browning's "Soliloquy of the Spanish Cloister" the monk who is narrating shows no sign of desiring anything that Brother Lawrence has or does. On the contrary, the narrator snips off the buds of the melon plants--ending all possible melon growth--that are meant to grace the supper tables come summer. This is not covetousness. Furthermore, the narrator despises the manner in which Brother Lawrence's robust appetite displays itself. As a consequence of this disgust, the narrator spends an entire stanza on describing the care he gives to his own cutlery and plateware. This is not envy.
What we have in Browning's "Soliloquy of the Spanish Cloister" is a wittily ironic picture of flourishing hatred: The narrator despises Brother Lawrence. If the narrator held secret longings to garden but was prevented by a perennial yellow thumb (the opposite of the proverbial green thumb), and if he harbored secret desires to be an expert on the signs of the weather, we might say that he was acting out of envy and was coveting Brother Lawrence's privileged position as gardener and weather aficionado, but these hypotheticals are not the case.
As to immorality, which spans a whole range of behaviors and attitudes, Brother Lawrence shows no sign of anything but cheerful absorption in his pleasant tasks of bringing forth life from the soil and is, by the narrator's own admission, oblivious to "brown Delores" who squats telling stories beyond the Convent walls, with her "Blue-black, lustrous" tresses shinning in the sun. On the other hand, the narrator is very well aware of "brown Delores" and can describe her and her activities to a turn, as the saying goes. When this propensity to engage his mind on subject matter outside the bounds of his brotherhood vows is added to his propensity for seething hatred, it is fair to conclude that the narrator is, on several counts, an immoral man in contrast to the moral attitudes and behavior of Brother Lawrence.