The 15+15+45 Rule: A Masterclass in Curation

Proportion rules in floristry are scaffolding, not law. They exist because they produce reliably acceptable results quickly, which matters when you are building forty arrangements before eleven and cannot deliberate over each one. Knowing which rule you are using — and when to abandon it — is more useful than knowing any particular rule.

The Rules Actually in Circulation

Several proportion conventions get quoted in the trade, with varying provenance and varying usefulness.

The most widely taught is the height ratio: the arrangement should stand roughly one and a half to two times the height of its vessel, measured from the rim. For a wide low bowl the same ratio is applied to the width instead. This is genuinely useful and it is the one worth internalising first.

The 60-30-10 split is borrowed from interior design, where it governs the distribution of a dominant colour, a secondary and an accent. Applied to flowers it produces palettes that hold together, and it is the reason a scheme with one clear dominant colour usually beats a democratic mix.

The thirds convention — one third vessel, two thirds material, or the inverse for a tall vase — is a simplification of the height ratio and produces similar results.

Formulations like 15+15+45 circulate as studio shorthand for a three-tier build: a short inner tier, a mid tier, and a long structural tier, with the numbers standing for relative stem lengths in centimetres rather than any universal constant. It is a working method rather than an industry standard, and treating it as canon is a mistake — but as a way of thinking about tiers it is sound.

What All of Them Are Approximating

Every one of these is a rough attempt at the same underlying thing: an arrangement needs a clear hierarchy of scale, and the eye needs a dominant element to settle on before it explores.

An arrangement where everything is the same length is inert. One where the tiers are too far apart falls into separate pieces that do not read as one object. The rules are all attempts to land in the workable band between those failures, and any of them will get you there.

Which is why arguing about the specific numbers is beside the point. What matters is that you decided on a hierarchy deliberately rather than letting the stems fall where they were cut.

When to Break Them

Three situations, all common.

When the flower has its own architecture. A single stem of gloriosa, a Crown Imperial, a branch of blossom — these carry a form that any proportion rule will flatten. Place them according to their own line and build around them.

When the setting overrides. A dining table imposes a height ceiling that no ratio survives. A tall narrow console imposes a width limit. The room wins, always, and an arrangement built to the rule and wrong for its position is simply wrong.

When the style is the point. Ikebana-influenced work uses its own proportional system entirely. Maximalist work deliberately compresses the tiers. Neither is improved by imposing a general-purpose rule on top.

The One That Matters Most

If you keep only one, keep the height ratio, because it fixes the most common domestic error: an arrangement too short for its vase.

People cut stems to fit a vessel, then cut again to tidy the shape, and end up with a dense low dome sitting inside a tall vase — which reads as an arrangement that has sunk. The ratio prevents it, and it costs nothing to apply.

The corollary is that vase choice should follow the flowers rather than the other way round. Long-stemmed material wants a vessel it can stand well clear of; short-stemmed material wants something low and wide it can spread across. A single tall vase used for everything guarantees getting this wrong most of the time, which is why our Essential Glass Vase exists alongside lower forms rather than as a universal answer.

A Note on Where These Rules Came From

Worth a moment, because provenance affects how much authority to grant them.

Ratio conventions in Western floristry largely descend from design education rather than from any floristry-specific research, and a number trace back to general compositional theory — the rule of thirds from picture-making, proportional systems from architecture, colour splits from interior design. They arrived in floral training because they work reasonably well, not because anyone tested them on flowers.

That is not a criticism. It does mean these are conventions with a good track record rather than discovered facts, and anyone presenting a specific ratio as the correct one is overstating what is known.

Where Proportion Stops Mattering

Once an arrangement is beyond a certain scale, proportion rules stop governing and sightlines take over. A gala centrepiece is designed to a height constraint, not a ratio. A lobby installation is designed to the architecture. In both cases the rule is imposed from outside and the internal proportions simply have to work within it.

That is the honest hierarchy: the room decides, then the flowers decide, then the rules apply to whatever freedom is left. Beginning with the rule and hoping the room cooperates is how arrangements end up technically correct and obviously wrong.