True, Wilbur is literally talking about gardening here, but we can't help but notice the word choice "raucous" (as in rowdy, which definitely has some sexual connotation attached to it), and the line break at "bed." Raucous bed?! C'mon, that's got to be a tongue-in-cheek move on Wilbur's part.
Isn't this better (12)
"This"—what exactly is "this?" Wilbur doesn't ever say it outright, but we're thinking it could very well be sex.
Think of all the time you are not Wasting, and would not care to waste (13-14)
Similar to love, this line makes us think there's nothing more important that what the couple is doing.
You've saved, and so may spend on this, (18)
"This" is back. You could definitely replace both "this" in line 12 and 18 with "having sex" and it would totally work the same way.
You who had rather lie in bed and kiss (19)
This kissing they speak of may very well lead to more—at least that's what they teach us in health class.
It's almost noon, you say? If so, (21)
They've been in bed for a while! They're probably busy—uh—getting busy.
Time flies, and I need not rehearse (22)
Time flies when you're having fun! Not to be too "mind in the gutter" about it, but it's quite possible their fun together includes having sex.
[…] and some fine Ruddy-skinned pears. (27-28)
If you think about the shape of a pear, it kind of looks like a woman—especially the curve of the pear as the hips of a woman. And instead of saying, "red pears," Wilbur writes "ruddy-skinned" to make us think of flesh, flush or pink flesh for that matter, which makes us think of a nude woman, and (finally), makes us think of sex (as if we weren't already convinced).