Keep an eye out for white powdery mildew on plants. If possible, remove the affected parts and spray with a fungicide.
Look for aphids on the underside of leaves - rub them off by hand, spray with an insecticide or try a natural pest control such as lacewing larvae.
Crush scarlet lily beetles on your lilies. Also check for the sticky brown larvae on the underside of leaves.
Clip evergreen hedges while they are in active growth.
Check plants in your greenhouse daily and water them if the soil is dry.
Turn the compost in your bins every month.
Pick sweet peas as soon as they flower to encourage more blooms.
Dead-head roses if they are repeat-flowering types.
Dead-head and cut back oriental poppies after flowering.