BOUGAINVILLEA BONSAI

The Bougainvillea Bonsai: An Explosion of Tropical Color

Bougainvillea ( Nyctaginaceae family) is the undisputed queen of the Mediterranean summer. If you are looking for a bonsai tree that will impress with its vibrant colors, this is the right choice. A little trivia that always throws beginners off: what we call colorful "flowers" (pink, purple, red or orange) are actually bracts, or modified leaves. The real flowers are those little white tubes in the center. It is a "lively" plant that requires sun, heat and a little "wrist" to tame, but it repays with unique visual spectacles.

Origin & species

Native to the tropical forests of South America (mainly Brazil), Bougainvillea is a climbing or shrubby plant. Bougainvillea glabra (more compact) or Bougainvillea spectabilis are often used in bonsai. Being a tropical species, its metabolism is heat-related: it loves our summers but fears our harsh winters.

Exposure and Microclimate

There are no half measures here: the Bougainvillea wants direct sun. The more sun it gets, the more colorful and abundant the bracts will be.
Shade inhibits flowering and stretches the vegetation, making it weak. Only in extreme heat (above 40°C (104°F) in a small pot) can it be lightly sheltered in the middle hours, but it is one of the few plants that laughs in the face of the August sun.

Watering

Water management is the secret to flowering. Bougainvillea is a plant that produces only green leaves if overly pampered with water.
Water generously, but allow the soil to dry well between waterings. Slight water stress (letting the soil dry well) often stimulates flower production. Be careful, however: if the leaves droop too much, water immediately.

Water quality

Fears limestone and water that is too hard, which in the long run causes chlorosis (yellowing of leaves). If you can, use rainwater or slightly acidify tap water by letting it sit. If you see the leaves turning pale green with dark veins, it is asking for iron (iron chelate).

Substrate

Needs draining soil to avoid root rot, which is its Achilles heel, but a bit more acidic than other species.

  • Ideal mixture: 60 percent Akadama (for drainage and structure) and 40 percent acidic potting soil or Kanuma (if available) or quality blond peat.
  • In very hot areas, increase the organic part so you don't have to water three times a day.

Repotting

Forget the rules for homegrown plants. Being tropical, Bougainvillea should be repotted when it is warm, in late spring (May-June), when night temperatures are stable above 15-18°C.
Caution: The roots are fragile and fleshy. It does not like drastic reductions in the root system. Be gentle and use a slightly deeper pot if possible.

Fertilization

It is a voracious plant. During the growing season (May to September) it should be fertilized regularly.
To encourage flowering, use a fertilizer with more Potassium (K) and Phosphorus (P) and less Nitrogen (N) from late spring onward. Excess nitrogen will give you a beautiful green bush, but without a thread of color.

Flowering and fruiting

Flowering occurs on new branches. To get it compact, you need to prune off any branches that get too long. After the first summer bloom, if you prune lightly and fertilize, you may get a second bloom in the fall.

Structure pruning

"Heavy" pruning is done in late winter/early spring, before vegetative growth resumes. Bougainvillea heals poorly and slowly: always protect large cuts with mastic and try not to make huge cuts on the main trunk unless strictly necessary, because the wood tends to shrink.

Maintenance pruning

This is a fast-growing species that throws off long branches like whips. During the summer, shorten branches that are too long to maintain shape, cutting back after 2-3 nodes. Remember that flowers are born at the apex of the new shoots: if you continually shear everything, it will never bloom. You must find the balance.

Tying & bending

Young branches are very flexible, almost herbaceous, but be careful: they lignify quickly and become hard and brittle.
Watch out for thorns! There is often a thorn hidden under the leaf axil that can make tying painful. Use the wire when the branch is still green but starting to harden. Check often because it grows fast and the wire etches right away.

Diseases and pests

If grown in sun and air, it is healthy. However:

  • Aphids: They love tender shoots and buds.
  • Red spider mite: Appears if the air is too dry.
  • Cotton bollworm: The real enemy. Hides in bark folds or under leaves.

Winter & protections

This is the critical point. Bougainvillea does not tolerate frost.
In northern Italy it should be brought into a heated greenhouse or indoors (in a very bright, not too warm room) as soon as temperatures drop below 5-7°C. In the South it can stay outside, but in a position sheltered from the cold wind and perhaps covered with nonwoven fabric (TNT) on the coldest nights. If it loses its leaves in winter do not worry too much, it is a defense mechanism; it will grow back in spring.

Annual calendar

  • January-February: Rest (in greenhouse in the north), minimal watering.
  • March-April: Awakening, start light fertilizing, bring back outside if minimums allow.
  • May-June: Repotting (ideal time), heavy watering, full sun.
  • July-August: Flowering, control spider mite, light green pruning.
  • September: Second flowering possible, potassic fertilizer.
  • October-November: Retreat to greenhouse (in the north), water reduction.
  • December: Protection.

Useful products for this bonsai

Frequently Asked Questions about Bougainvillea

Why does my Bougainvillea make lots of leaves but no flowers?
It probably gets too little sun or too much nitrogen fertilizer. Move it to full sun and discontinue the nitrogen in favor of a flowering fertilizer (with potassium). Sometimes leaving it a little "dry" for a few days stimulates flowering.

Did it lose all its leaves in winter, did it die?
Not necessarily. If the wood scratched lightly with a fingernail is still green underneath, it is alive. It is a reaction to cold or low light. In spring, with warm weather, it should sprout again. Be careful, however, not to drown it with water while it is leafless.

How do I get the trunk to swell?
Bougainvillea in pots swells slowly. The trick is to let sacrificial branches (meters long) grow for a season or two without cutting them back, fertilizing a lot. This will make sap "pull" and enlarge the base.

Can I tie off the old branches?
Not recommended. Old branches of Bougainvillea are stiff and will snap cleanly without warning. Better to work with directional pruning or tie only the young branches that are still green/semi-woody.