Bougainvillea is a tropical perennial plant that can flower in the Spring from as early as May all the way until the late Fall in warm climates.
The reason for bougainvillea not flowering is because the plant is stressed. Bougainvilleas require 6 hours of direct sun and flower to their best when day length is less then 12 hours. Boggy soil prevents bougainvilleas flowering and too much fertilizer causes lush foliage with fewer flowers.
Keep reading for more information on why your bougainvillea may not be blooming and what you can do to ensure a good display of flowers next season…
1. Too Much Water Prevents Flowering
Bougainvilleas are drought tolerant plants that actually thrive in dryer soils with infrequent watering.
A common mistake for gardeners is to take the same approach as roses or hydrangeas etc. and try to water frequently so that the soil is consistently moist.
If you water bougainvilleas too frequently the plant becomes stressed as this is contrary to its preferred conditions in its hot and dry native environment which then results in fewer blooms.
For bougainvilleas it is best to think of them having the same watering requirements as Mediterranean plants such as lavender and delay watering until the soil is somewhat dry to a winters depths.
This emulates their natural preferred flowering conditions (they flower during the dry season in their native South America) and the water stress triggers the develop of the colourful flowers (and bracts).
I personally water my potted bougainvilleas once every week during the Spring and Summer and find this is the ideal balance to meet the moisture requirements and also stimulate blooms.
Give bougainvilleas a good soak each time you water to the extent that water escapes out the base of the pot.
This encourages the roots to establish in the soil and further improves their drought tolerance and ability to access nutrients.
Bougainvilleas that are established, planted in garden boarders often do not require any additional watering and thrive and flower with neglectful treatment.
(If your bougainvillea is not growing, read my article why is my bougainvillea dying to save it).
2. Too Much Fertilizer Encourages Foliage at the Expense of Flowers
Frequently applying fertilizer to bougainvillea plants can stimulate lots of lush green foliage and stems at the expense of flowers.
Bougainvilleas are hardy plants and can adapt to a wide variety of soils. The most important soil characteristic for encouraging blooms is that the soil is well draining rather then overly fertile.
Well established bougainvilleas planted in garden soil generally do not require any additional fertilizer for flowering.
However if the Bougainvillea has been growing in a pot for several years then the roots may exhaust the potting soil of nutrients, in which case some additional fertilizer may be required for Bougainvillea to flower it best.
The key is to only use a half strength all purpose NPK (Nitrogen Phosphorous and Potassium) fertilizer in the Spring to provide the plant with the required nutrients for growing and flowering without overwhelming the soil with Nitrogen.
Scale back your fertilizing schedule for bougainvillea if you are not seeing any blooms in the Summer and just leave the plant for a year.
Bougainvilleas tend to thrive on neglectful conditions and can flower in fairly nutrients sparse soil with a high content of sand or perlite but tend to do best in well draining loam soil.
The following year without added fertilizer the bougainvillea should be in a better condition to display flowers.
3. Not Enough Direct Sun Light For Flowering
Bougainvilleas are native to tropical South America where it enjoys full sun.
If planted in the shade the bougainvillea tends to grow more vegetation and fewer flowers.
For optimal flowering locate your bougainvillea in a sunny spot with at least 6 hours of sun to ensure a good bloom.
This is one of the reasons why its is best to grow bougainvillea in pots to locate in full sun during Spring, Summer and Fall and so that you can take the plant indoors during Winter for protection as it is not cold hardy (USDA hardiness zones 9b and 10).
Interestingly it is not only the intensity of the sun that is important for flowering (full sun rather then indirect light) but also the day length influences how well the bougainvillea flowers…
4. Bougainvillea Flowers Best with Shorter Day Lengths
Whilst Bougainvilleas prefer intense sunshine during the day, they actually flower best with day lengths that are shorter then 12 hours.
This preference for shorter day for promoting flowering is a due to adaptions to its natural environment within the tropics where the days or shorter then nights during the dry season.
So to encourage your bougainvillea to flower it is important to replicate the prefer light conditions of it natural environment.
In northerly latitudes where the sun can rise very early and set very late a common problem is a very long day length that inhibits flowering (New York has peaks at 15 hours of daylight on June the 21st, UK has as much as 16 hours of daylight) so to get the best out of your bougainvillea it may be necessary to either:
- Find a place in your garden that is shaded in the afternoon or for serious flower enthusiasts…
- Place a black cloth over the plant in the evenings to replicate the shorter days of its native tropical environment to promote flowering.
If your bougainvillea is indoors then it can be easier to ensure the Bougainvillea is in less then 12 hours of light although artificial lighting can also inhibit flowering so choose a location with direct sun during the day and shaded or even darker evenings where it is not in the glare of house lights at night.
5. Slow Draining Soils Prevent Blooms
Another reason for bougainvilleas not flowering is because of boggy soils that retain too much water.
Slow draining soils has the same effect as water too frequently. With clay soils or boggy low lying soils the roots do not have the opptuntity to dry out between bouts of watering.
In gardens with damp soils (and cold climates) plant bougainvilleas in pots or containers.
Pots have more favourable drainage conditions compared to garden boarders and it is far easier to customize the potting mix to suit the preference of the plant.
For healthy bougainvilleas that stay free of root rot and flower to their full potential use a potting mix of good quality multi purpose compost and add in some horticultural sand, grit or perlite to improve the drainage.
This well draining soil mix emulates the dry soil conditions of the native range of bougainvilleas and ensures that the plant has the chance to bloom without suffering because of boggy soil.
6. Warm Temperatures Increases Blooms
Bougainvilleas prefer warmer temperatures for more blooms. Ideally the night temperature should be around 65°F (18°C) is optimal for flower development however bougainvillea is adaptable and can flower with cooler night time temperatures.
If the weather is unseasonable cool or cold during Summer then this can harm the prospects of bougainvillea flowering and the plant is best take indoors or protected with fleece to maintain blooms.
Bougainvilleas are not cold hardy and require Winter protection in cold climates so plant them in a pot or container to move the plant indoors in the Fall.
For cooler climates a warm, sunny window is often the best place to grow bougainvilleas and ensure that they bloom.
(Read my article for how to save a bougainvillea that is losing its leaves).
- The reason for bougainvillea not blooming can be because of damp soil, too much fertilizer, not enough direct sun and due to day lengths longer then 12 hours.
- Bougainvilleas require somewhat dry soil, warmer temperatures at night 6 hours of direct sun and less then 12 hours of day light for flowering.
- Too much fertilizer or too much shade generally results in lots of foliage at the expense of flowers.
- Do not water bougainvillea too frequently or plant in slow draining soils as too much water prevents flowering. Plant bougainvilleas in pots for improved drainage.