Quote:
User story: As a homeowner, I'd like a lovely green backyard with various trees.

Meh. Send user story back to user for additional info. Can't estimate time required, nor are any valid done conditions discernable. How much upkeep is user willing to do? Are other colors okay besides green (how about a lilac)? Does user prefer coniferous, or deciduous trees? Fruit or nut bearing? Any HOA or zoning restrictions? Shade-bearing, or decorative?

Quote:
User story: As a homeowner, I'd like a lovely green backyard with various trees.
Story points: 13, or maybe a 20
Task: Buy supplies from local home improvement store
Task: Plant 5 apple trees
Task: Plant 6 bushes

... end of sprint ...

But I'm allergic to apples!