Planting Bougainvillea: Pot Size, Soil and Root Handling

Choose a pot that looks too small

The instinct with a vigorous climber is to give it room. Do the opposite. A bougainvillea in a generous container spends a year or two filling that container with roots and top growth, and it will not flower properly while it is doing so. A crowded root ball is one of the two levers, along with drought, that make this plant color up.

For a young plant, move up by one size only, from a six inch (15 cm) pot to an eight inch (20 cm) one. A mature specimen is perfectly happy long term in a twelve to sixteen inch (30 to 40 cm) container and can stay there for four or five years. Plants that flower spectacularly on balconies are almost always in pots that look far too small for the amount of growth above them.

Terracotta suits it better than plastic because the sides breathe and the whole root ball dries faster, which makes the deliberate dry cycle easier to run. Weight matters too: a plant carrying six feet (1.8 m) of growth catches wind, and a heavy pot stops it going over.

Drainage is non-negotiable. Bougainvillea tolerates drought superbly and standing water not at all. A pot with one small hole sitting flat on a paved surface will hold a saucer of water at the base that you cannot see, and that is the classic way to lose an otherwise healthy plant.

The roots are brittle and barely hold together

This is the fact that separates bougainvillea from almost everything else you will plant. Its root system is coarse, fragile and only loosely bound into the compost. Lift a plant out of its pot carelessly and the root ball can simply fall apart in your hands. The plant will not die outright, but it will drop every leaf, sulk for months and give you no color for a full season.

So the rule for planting is minimum disturbance. Do not tease the roots out. Do not score the sides of the root ball. Do not shake off the old compost. Every piece of standard planting advice about loosening congested roots is wrong for this plant. Slide it out intact and set it down intact.

If the plant is stuck, cut the pot rather than pull the plant. A plastic pot costs nothing and a broken root ball costs you a year. Support the base of the root ball with a flat hand or a piece of board while you move it, rather than lifting the plant by its stem.

The same fragility is why bougainvillea resents being moved once established, and why container growing suits it. You can shift the pot to follow the sun or bring it under cover without touching the roots at all.

Wear thick leather gloves and long sleeves for any handling. The thorns are hard, curved, set close to the stem and often hidden under leaves. They tear rather than prick, they catch you when you pull your hand back, and scratches from them commonly go red and inflamed. This is not a plant to handle bare-armed.

Getting it in the pot

The whole operation should take five minutes and involve as little contact with the roots as possible. Have everything ready before the plant comes out of its old container, because a bare root ball sitting in the sun is losing time.

1. Mix a gritty, lean compost Two parts standard potting mix to one part coarse grit, perlite or sharp sand. Avoid anything sold as moisture-retentive and avoid rich composts loaded with slow-release nitrogen, which will drive leaf growth at the expense of color.
2. Part-fill the new pot Add enough compost that the top of the old root ball will sit an inch (2.5 cm) below the rim. Firm this base layer lightly so the plant does not sink later, and check the depth with the plant still in its old pot rather than out of it.
3. Cut the old pot away Slit a plastic pot down two sides with a knife and peel it off, rather than inverting the plant and tapping it out. Keep the root ball supported from underneath at all times and keep it level.
4. Set it in without touching the roots Lower it straight down into the hole at the same depth it was growing before. Planting deeper does not encourage rooting in this species and invites stem rot at the collar.
5. Fill the gap and firm gently Trickle compost into the gap around the sides and tap the pot on the ground to settle it rather than pressing hard with your fingers. You want the gap filled, not the root ball compressed.
6. Water once, then leave it Give one thorough soak to settle the compost and then withhold water until the surface is dry to a finger's depth. A newly potted plant with a barely functioning root system in constantly wet compost is the fastest route to root rot.

Position, support and the first month

Bougainvillea needs full, direct sun. Six hours a day is the minimum for any color worth having and eight or more is better. A plant in bright shade will grow perfectly well and never flower, and no amount of drought treatment fixes insufficient light. Choose the sunniest position you have and accept the plant will be large there.

It also wants warmth at the roots. A pot standing on cold, shaded paving will be sluggish even with the top in full sun. Raise it on pot feet in a spot that catches morning light on the container itself.

It is not a self-clinging climber and it has no tendrils. The thorns are hooks that let it scramble through other vegetation, which is not the same as attaching to a wall. If you want it on a trellis or a frame, tie the main stems in loosely with soft ties while they are young and still flexible, because an older stem will snap rather than bend.

For the first month after planting, expect a pause. New leaves may not appear for three or four weeks and the plant may shed a few older ones. Do not respond by watering more or feeding. Keep it dry, keep it warm, and wait. Growth resumes once the roots have re-established, and only then is it worth starting the flowering cycle.

Note what you planted into

Bougainvillea is on a slow clock. It might be four years before you touch the roots again, and by then nobody remembers what went into the pot. A few lines written now save a lot of guessing later.

Record the date you potted it, the finished pot size, and the compost mix you used including the proportion of grit. When the plant eventually needs moving, that mix is what you want to reproduce. Note where the pot stands and roughly how many hours of direct sun it gets there, so that a poor flowering season can be checked against light before you start changing anything else.

Write down how long the plant took to push new growth after planting. That figure tells you what is normal for your conditions, so the next time a plant sits still for a month you know whether to worry.