A bougainvillea is a tropical thorny vine that can grow 40 feet tall. Bougainvillea has the nickname "paper flower" because the flowers on this vine are thin and resemble paper. Having a good root system is important for the bougainvillea. If you want to ensure that your bougainvillea roots stay healthy, you will need to fertilize them on a regular basis.
Choose a 21-5-20 water-soluble fertilizer to feed your bougainvillea. Moisten the soil around your bougainvillea, but don't soak it. Plant Care advises against applying fertilizer to bougainvillea vines when the soil is dry.
Wear long clothing before working with the fertilizer, and put on any safety gear recommended on the fertilizer's product label.
Apply the fertilizer to the soil around the bougainvillea vine's roots. Texas A&M University recommends that you do this at half the strength listed on the fertilizer label.
Moisten the soil again with water from a garden hose. This will send the fertilizer down into the soil where the roots of the bougainvillea can reach it.
Repeat. Bougainvilleas need to be fertilized once per month, unlike many other plants that only require fertilization twice per year.