Although day temperatures and humidity levels remain high, and the typhoon season has not yet ended, Autumn is just around the corner, so it’s time for me to take stock of my plants and decide what might be worth propagating, and what should be pruned or discarded.
Orchids had their year’s ration of high potassium fertiliser (to encourage flowering) back in May. It’s supposed to last for six months, which will take us to the end of their current growing season. Now they will need very little attention until next spring.
Most other plants are overdue for their six-weekly dose of guano pellets. The virtually equal numbers in the NPK rating indicate that this gives all-round benefit. By late August, I will give any surviving herbs a half-dose of guano to introduce them to the idea that there is life after summer. Hibiscus and a few other heavy flowerers need an extra helping of potassium in the form of bone-meal to increase the size and number of blooms.
As for the bougainvillea, the following guide should help with any questions you have about getting the most out of this ever-popular Brazilian native in Hong Kong.
Some people will tell you to feed bougainvillea; others will give you the opposite advice and tell you not to water it. I have a very old and aggressive but beautiful bougainvillea that has managed very well without fertiliser or anything except rainwater all these years. But if you feel your plant looks unthrifty, try a little all-round fertiliser. Most Hong Kong soil is acid, which suits these scramblers very well. Some trace elements might be in short supply, so if the green leaves are suffering, sprinkle the occasional pinch of soluble iron granules around the roots. Bougainvilleas like plenty of organic matter in the soil, which should drain fast as these plants have rather shallow, brittle roots that are prone to rot if they have wet feet for too long.
Some bougainvilleas are already showing colour, but others are still shy about flowering for the moment. If you buy one of these tropical beauties from a knowledgeable nursery, it’s worth asking about the flowering season and the growth habit. Hybridisation continues to produce ever brighter, more spectacular colours, although not all seem suited to our conditions.
Incidentally, what we refer to as bougainvillea “flowers” are actually showy bracts surrounding the inconspicuous flowers. But I would have difficulty getting my mouth around the word “bracts”, whereas “flowers” trips off the tongue – not to mention my computer keyboard – very easily!
Bougainvilleas need at least six hours of full sunshine if they are to look their best. In their native habitat they flower throughout the year, but they rarely show much colour during the typical Hong Kong summer. Dry weather triggers the best flowering season on new growth, so whether they are in a pot or in the ground, the plants should be heavily pruned now to force them to put up new shoots ready for the anticipated flowering season ahead.
Some bougainvilleas never flower, regardless of how well they are treated. If you are sure that you provide ideal sun and other requirements yet your shrub remains a defiant, healthy green, try drenching it with two tablespoons of Epsom salts mixed into four litres of water. The magnesium and other minerals might supply something that is lacking in your soil, or maybe the shock will be sufficient to make the plant produce some colour. Some people swear that this mixture also works as a safe lawn pesticide.
If all else fails to make your bougainvillea bloom, give it to someone else, who will doubtless soon have it flowering like mad to make up for lost time. Best to send it somewhere at a distance where it cannot mock you every day!
Be picky when you select a new bougainvillea. Take your time when you survey the many gorgeous colours and combinations. In the past, the most unusual plants were from Malaysia and Thailand but, these days, Chinese growers have perfected all the necessary techniques to produce plants of comparable quality. Some stunning bi- or tri-colour plants have been produced in recent years. Personally, I am not keen on bougainvillea with variegated leaves, as I feel that the colours show up best against plain green, but that feature offers yet one more option at selection time.
My all-time favourite produces random combinations of pink-and-white bracts. But after over 20 years it is a massive grower and hard to keep in check. Consider where and how you want your plant to grow. It can scramble upwards and form a tree-like umbrella or a formidable hedge. If you have the patience and the skill you can clip it like a standard rose, create a peacock, a dragon or indulge in any other flight of fancy that might appeal.
If you would like your bougainvillea to cover a fence or wall, start training it when you first acquire it. Secure new shoots in place as soon as they emerge and remove unwanted or unruly growth while it is still soft.
Be careful how you handle bougainvillea as the thorns can cause irritations and infections – soap and water followed by a little tea-tree or antiseptic cream is always a wise precaution if you sustain a scratch.
All bougainvilleas should be pruned hard once a year. When you prune even a small potted plant, remove at least half the growth on a spray – two flowering points will emerge within about a month. With a large plant, use shears and don’t worry about subtlety.
The same advice goes for many other shrubs, especially wild growers like Holmskioldia (Chinese hat or Parasol). This should be cut back to less than one metre high and then left to grow as it wishes through the winter. The flowers (bracts again) keep their colour for months and the local sunbirds and flower peckers queue up for a chance to get their share of nectar.
Exceptions to the crewcut lineup include Megaskepasma (Brazilian cloak) which should be cut very little, if at all – unless you want a season without colour. And you should definitely not touch your Clerodendrum wallichii at this season if you hope to have the full quota of beautiful cascading white flowers in November and December.
Lastly, get your winter annual flowers and vegetables off to a flying start by sowing the seeds under cover or even indoors where they will be safe from heavy rain. Keep some seed safely in reserve in case you need to make a succession of sowings.
Jane Ram is a long-time Hong Kong resident, a journalist and an avid gardener; she’s also the immediate past chair and long-time committee member of the Hong Kong Gardening Society.