Take a good size plant. Always choose a plant with a tree-like structure, full of branches, and with a thick main stem/trunk. Take the plant out of the polybag if you buy it and then be careful to remove excess soil from its root ball. Be gentle with roots so you do not damage them. Prune (remove) unwanted roots with a help of clean sharp secateurs.
Pruning roots is a normal part of helping your houseplants grow. You just have to be careful whenever handling the structure of the root of any plant. Be sure to give plenty of water after you do root pruning on any of your plants. Take a medium-sized. I will prefer you to take a bonsai pot, which is 20 inches in length and 6-7 inches in depth otherwise you can take a normal pot with 12-15 inches of diameter and 8-12 inches of depth. if you're planting the bougainvillea in a container, make sure to choose one with plenty of drainage holes, since bougainvillea hates to have "wet feet."
Cover the holes with stone for effective drainage. Bougainvillea loves soil that drains well and does not hold on to moisture for that we will use garden soil compost(vermicompost) and River sand in an equal proposition. Soil needs to be rich yet have excellent drainage you want your bougainvillea to take the moisture it needs and then have all the excess drain out. First, fill 2-3 inches of the pot with soil mixture. Position the plant according to your choice, press the root ball in the soil, and check whether the root ball is aligned correctly with the rim of the container.
Fill the pot with the soil mixture cover all the exposed roots and lightly pat the soil around the base of the plant. Bougainvillea has an extremely fine root system and should be planted in well-drained soil. Avoid soil mixes with high peat levels and water retention. These types of media retain too-much water and will contribute to root rot; be sure to select the well-draining media. Keep a gap of 1-2 inches between the rim of the pot and the soil surface for effective watering.
Remove all the exposed roots with a clean sharp secateurs. Always clean your pair of clippers with a disinfectant before using. You can use rubbing alcohol to prevent the spread of infectious diseases. Planting a succulent plant to avoid soil washout. After a few days remove it (this step is not compulsory). Water the mix thoroughly before moving the pot to a sunny corner.
After a few days remove the succulent plant from the pot as it was sucking essential nutrients from the soil. Adding color gravel as a mulch on the soil surface avoids any weed growth and this will also help to keep the soil moist for a longer period of time, especially during hot days.
WATERING: Bougainvillea plant weakens with too much watering, ending up with all leaf growth in place of flowers. water enough to keep the soil damp, but not so much that you leave the plant waterlogged. Use a fertilizer that should be high in phosphorous like DAP and NPK. This will force the plant to produce flower buds. It needs regular fertilization to produce more flowers throughout the growing season. Add one tablespoon after every 30-45 days. Make sure to add it away from the main stem to avoid root burn. Dig a small hole in the soil and gently place the granules into the hole and cover it with the soil. Water the plant immediately after adding fertilizer to the soil. This will allow the plant to absorb nutrients instantly.
LOCATION: You should put your bougainvillea in a place where it will receive at least 5-7 hours of sunlight every day. You can put it on the sunlit porch or at a south-facing window if kept indoors.