Bougainvillea plants are members of the genus Bougainvillea, a group native to South America. The plant was first classified in the late 18th century, and is now grown as a tropical ornamental. This plant prefers strong sun and hot weather. It also has particular nutrient requirements that can make fertilising it difficult. Organic gardeners should fertilise their Bougainvillea plants regularly to ensure strong growth and vibrant blooms.
According to gardening writer and lecturer Pat Welsh, Bougainvillea plants require significant amounts of nitrogen. Protein-based organic fertilisers, such as composted manure and blood meal, contain higher levels of nitrogen than wood chips and other plant-based soil amendments. When using animal manures, choose only dry manure containing no bedding material. Additional bedding material, such as straw, can raise the carbon content of the fertiliser and encourage nitrogen binding, a process that prevents fertiliser nitrogen from being available to plants.
Bougainvillea plants also require iron and other micronutrients, especially during their blooming season. These nutrients can be added directly to the soil. They work best in chelated form, in which the iron is most readily available. Iron fertilisers are also available as iron sulphate, which can leave rust stains on concrete and other nearby surfaces. Avoid using iron sulphate in alkaline soils, which can bind the iron and keep the plant from using it to grow. Iron sulphate is an acceptable soil additive in acidic soils, where it is less likely to bind.
Because Bougainvillea plants require regular light applications of fertiliser, liquid forms are more effective than solid fertilisers. Organic fertilisers such as manure or blood meal may need to be soaked in water to create a fertiliser tea that can then be applied to the soil around a Bougainvillea. Commercial liquid organic fertilisers may also be used, but gardeners should check their nitrogen and other nutrient balance to ensure they choose the right product for their flowers.