Possible Clues:

• Allergen with its own index
• Plant spores
• With 124-Across, dreaded time of the year for many allergy sufferers
• Exercise involving oxygen 50/50 with nitrogen, this helps growth
• Source of seasonal sneezes
• Powder from some plants, an allergen for some people
• Food for the bees
• The Count in summer produced sample of the menu from The Centre
• Staff covering large garden at the back getting fertiliser
• Plant powder that causes hay fever