The ground is rock hard, the air is crisp and the trees are bare. But while the yard is sleeping, Colorado gardeners are not just twiddling their green thumbs and waiting for spring — they’re also preparing and scheming. “The off-season really is when most gardeners are thinking about and daydreaming of their next growing season,” said Kim Zimmerman, a Colorado master gardener and the founder of Rowdy Poppy, a micro flower farm and design studio in Denver.