The title sequence, by graphics designer Douglas Burd, was shot on 35mm film and used quantized color levels in stark relief against a black background. Burd was killed during production when his self-made plane crashed during a flight.
Each 8-foot-tall triffid prop concealed an operator on a go-kart seat in a fan-cooled, 5-foot diameter base. The base was modelled on a ginseng root. Two of the props were later used in a carnivorous plant display at the Natural History Museum in London, England.
Mortar bombs are ineffective against Triffids because they share a tree's ability to take great damage without lethal harm. Or they can wait for their prey to emerge just by putting down roots to lull people into a false sense of security and then suddenly spring to life and attack, even a passing car, covering the windscreen in their poison. Spraying the ground with arsenic can deter Triffids but only temporarily. If they do find a way in they'll surround a house right up to the windows. Wearing protection from the Triffids includes thick clothing, gloves, a leather helmet, goggles and a mesh mask. You could hack your way through with a carving knife wearing all this, but their poison can penetrate a mask if there are enough of them. Triffids can collapse a fence (even if reinforced) by concentrating their efforts, even if it means dying in the attempt. Triffids can be electrified but not without a steady power source.
Elisabeth Sladen, who had worked for producer David Maloney when he was a director on Doctor Who, was offered a role.
You can hear Triffids in the night with the intermittent rattling of their hard sticks against their stems but they can't pass quietly over shingles.