Question
would appreciate some help with our Bougainvillea which we bought about two months ago from a local garden centre when it was in full bloom and looking lovely.
After a few weeks its leaves started to turn yellow and drop off and over half have gone. The majority of the flowers have also dropped off.  We have kept the plant in its original pot(filled with a fibrous-looking compost) in our conservatory which has not had any extremes of temperature and we have followed the care instructions supplied. These recommend keeping compost damp but not over-wet
The stalks which previously carried the flowers have gone brown

There is a fair amount of new growth developing but even these leaves are yellowing a little.
Can you offer any advice
Thanks


Answer
Bougainvillea spectabilis is a plant made for the tropical rainforest jungle -- somewhat cool at night (avg 68 degrees F in the Amazons) and warmer in the daytime (around 85 degrees F high).  It will tolerate semishade but its growth heads upward to reach the maximum amount of Sunlight.  Because its roots are designed for lots of air exposure, Bougainvilleas cannot take bad drainage or standing water -- which is why your garden center potted it in a 'fibrous' compost growing medium.  Since the rainforest gets around 80 inches of rain a year, you can see how those roots would adapt to the wet/dry situation.  Moisture is necessary, but so is air.

Moisture: This is the trick that you have to learn to grow Bougainvilleas.  Balancing act between watering and humidity.  I suspect the roots are too wet.  Overwatering will damage roots and nutrient uptake will cease, causing leaf drop; a clay pot will aggravate that.  Stop watering so much; use room temp water, make sure the plant is enjoying a ridiculous level of humidity, and let the growing medium dry out between drinks.

First, check to see if the plant is rootbound.  Pop it out of the pot and see if the roots are filling it up.  Sometimes nurseries keep plants pot-bound to trigger flowering.

If this is a plastic pot, switch to a Clay pot or other porous material -- this will help the roots get a little more air.  Go back to the garden center meantime and pick up a bag of the same growing medium.  It sounds like something they have had success with.  Bring the plant with you if needed to make sure you are on the same page discussing what you need to grow this plant.  Pain in the neck, but it is the best way to do this.

If the garden center was a long drive and you had picked this up while traveling, say, I'd tell you to repot it in Osmunda and/or Tree Bark, used for growing orchids.  But if you get the same material they are using, you will not make any unnecessary demands on the already stressed plant to adjust to a new growing medium.

Stressed plants often lose leaves as a result.  But Bougainvilleas will drop leaves for other reasons, too.  Is it getting a good amount of light?

Right now it's best to worry less about the flowering and more about your Bougainvillea's survival.  Once it's used to a new home, the flowers will follow.  When you see new leaf growth, fertilize with a nice organic fertilizer like Fish Emulsion -- smelly but effective, used in small diluted doses every time you water.  As it begins to settle in you can start dosing up with a chemical fertilizer like Miracle Gro or a Peters Orchid fertilizer with emphasis on the middle Phosphorous number.

These are not difficult plants.  They are different, and once you get used to it, like using a new computer, you'll be surprised at how easy it is to grow them.  Many people give up too soon, discouraged.  You can do this.  I guarantee it.