Flowers That Survive a Marquee

A marquee in August is a greenhouse. Half of what looks beautiful at nine in the morning is finished by the speeches.
The Heat Is the Enemy
A closed marquee in summer sun runs far hotter than the air outside, and soft-stemmed flowers go over in hours. Hydrangeas wilt first and most dramatically, then garden roses, then anything with a heavy head on a thin stem.
Tell your florist the wedding is in a marquee and ask directly what they would avoid. A good one will change the recipe without being asked twice.
What Holds Up
Chrysanthemums, carnations and alstroemeria are unfashionable and nearly indestructible, and used well they look nothing like a petrol-station bunch. Foliage does a great deal of work in the heat: eucalyptus, ruscus and beech hold their shape all day.
Anything woody and anything from the daisy family will generally outlast the reception. Dahlias look wonderful and will not, so use them where they will be photographed early.
Do Less, Later
Installations go up the morning of, not the night before, and in a marquee that rule is absolute. Anything sitting overnight in still warm air is a day older than it looks.
And the arrangements that survive best are the ones with the fewest stems. A jam jar of three things, repeated forty times down a trestle, still reads beautifully at midnight when a tiered centrepiece has collapsed.