Place collard greens into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer until just tender, about 10 minutes. Drain and transfer greens to a slow cooker.
Place the bacon in a large deep skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Crumble bacon; add bacon and grease to slow cooker along with chicken stock and jalapeno slices. Season with salt and pepper. Cook on Low for 8 hours or overnight.