The three main causes of poor flowering are:

• lack of sunlight. Agapanthus need at least 6 hours sunlight for good flowering and either won't flower well or at all if grown in heavily shaded positions.
• lack of fertilising.  Agapanthus need to be fertilised from time to time to bring out the best in flowering. 
•  overcrowding. Overcrowding occurs when the plants are not divided and are heavily root bound thereby placing the plants under considerable stress.

When planted out, we recommend in tropical and sub tropical areas to keep them on the dry side of moist to prevent root rot until established.  The best times to water agapanthus is early morning or late afternoon to optimise water penetration into the ground.   Never water your agapanthus on hot days during the middle of the day as the water can become trapped and heat up in the basal area of the plants.  

Agapanthus are soft foliage, drought tolerant plants.  The main causes of rotting are:

• poor soil drainage.  Plant in raised garden beds to assist in water drainage. 
• over watering. Agapanthus are drought tolerant an store water in their roots. Over watering can cause root oedema and collapse as oxygen levels are depleted in the soil.    
• over fertilising.  Fertilising in excess of recommendations can cause roots to burn off and die.
• pest damage. Plants damaged by pests may be velnerable to pathogen attacks particularly on hot humid days. 

This is often associated with overwatering rather than underwatering and is associated with roting and damaged roots.

Warm and damp weather can lead to pathogen attacks and cause the lower parts of the plants to rot. Ensuring soils around the plants are kept on the dry side of moist during hot weather is important to managing this if it occurs. Never water your plants during the middle of the day on hot days as the water can become trapped in the basal area of the plants and heat up.