Photo: Martin LaBar
Paula has written to me with some questions about her bougainvilleas. Located in planters on a sun-drenched balcony, they have flourished for years . However, she is concerned because they are now showing signs of distress with many petals [bracts] dropping prematurely. She conjectures that it may be for several reasons : namely that the containers (which are permanent and cannot be replaced with bigger ones) may now be too small. Or that in the present drought, the shrubs need more water, adding that the soil is “very dry”. She adds that they are given “fertilizer and new soil “ every time she visits Phuket.
I hope, Paula, that the following general remarks help you to address the issue.
Bougainvilleas, like adeniums and euphorbias, (equally popular container plants) are among the most resilient of shrubs. Though they are not as drought-proof as these succulents which store moisture in their tissues, they nonetheless need relatively little water. As your hotelier friend suggests, a soaking once a week should be sufficient. In the rainy season, your plants may need no additional water at all. That bougainvilleas thrive in hot, dry conditions is evidenced by the current spectacular displays around the island. I have never seen such a profusion of bloom.
In the present heat wave however, increase the dosage of water, but still allow the soil to dry out between applications. And ensure – and this is very important – that your planters drain effectively . In large measure how well they drain depends on the soil in your containers. It may have become too compacted. A peaty mix, moreover, is too water retentive. So try not to replace or top up with commercial compost. If you must use it, then add some ordinary soil. A sandy loam is best of all.
You say that the petals are falling. But they will drop at this time of year, especially if the plant is producing masses of colorful bracts (actually modified leaves). It does not mean, necessarily, that the plant is in poor health. But if leaf-drop is heavy and the foliage is discolored, then something is amiss: possibly soil that is actually too dry or has been suddenly watered too enthusiastically. Maybe, Paula, you have been a bit lavish with the granular fertilizer – which must always be used sparingly .
It is important to remember that bougainvilleas have two distinct growth cycles : the first is a period of rapid vegetative growth when the shoots are sappy and green leaves appear. If there is insufficient sunlight, the shrub will remain in this verdant state and may not progress to the second and flowering stage. Thus a specimen in deep shade may never bloom. But given oodles of sun – say a minimum of five hours a day – the plant will put all its energy into the production of clolorful bracts. How long the blooms remain on the prickly stems depends on the well-being of the plant.
You mention that the containers may now be too small. This is unlikely. Bougainvilleas have fine root systems, but given adequate nutrients, will cope with cramped surroundings. Unlike many woody shrubs, they are happy to be root-bound. That is one reason why they are often cultivated as “bonsai” specimens. Re-potting is not only unnecessary ; it will disturb the plant and retard growth. But they are heavy feeders and will need, as you know, light but consistent applications of fertilizer. Ideally use a phosphorus rich formula: a mix of – say N10- P15- K10 – is better than a standard one of 15-15-15. Added iron will ensure masses of vibrant color.
Finally you mention trimming. Bougainvilleas are tough cookies and in open ground will withstand any amount of pruning and cutting back. Obviously plants in pots do not need this kind of drastic treatment. But you are right to trim off what is frequently straggly growth. This trimming is best left till after the first display , so that new blooms can form on the shortened flowering spurs. Done that way, the all-important process of blooming should not be affected.
soil
green galoshes 