The firms competing are Crowders Nurseries, Hillier Nurseries, Palmstead Nurseries and Robin Tacchi Plants. There are expected to be more than 60,000 herbaceous plants required, grown in pots ranging up to five litres in size, as well as another 60,000 bulbs.
The bulbs include Allium, Crocus and Narcissus, while there will be more than 100 species of herbaceous plants, ranging from Achnatherum to Yucca.
Olympic Delivery Authority parklands and public realm project sponsor John Hopkins said: "The opportunity to grow and supply plants for this world-class garden is one that any nursery would relish.
"The London 2012 gardens are about bringing plants from all over the world, celebrating Britain's great tradition and passion for plant collecting, cultivation and garden design."