Possible Clues:

• Landscaper's bagful
• Gardener's supply
• Treat with compost
• Protection for roots left covered in a lot
• Mixture of straw, leaves etc spread on ground to protect plants
• Dressing for bed?
• Requisite for garden often kept in litres
• Plant protection
• Loose material spread by gardener to protect roots
• Spread a lot over surface of land