Blue Peter gardener Chris Collins will be a guest judge at Wisley
A "miniature Chelsea Flower Show" judged by Blue Peter's gardener will showcase budding gardeners from Surrey.
Pupils as young as four from 18 schools have designed and planted a metre squar (3.3ft) gardens for the half-term competition at RHS Garden Wisley.
The organisers said popular themes this year included environmentally-friendly features and edible plants.
Wisley curator Jim Gardiner and Blue Peter gardener Chris Collins will judge the entries on Friday 22 May.
Mr Collins said he was delighted to judge this competition.
"It is a great way to get children gardening with friends, and shows that even small spaces can make exciting gardening projects," he added.
Each of the tiny gardens is different, varying in colour, design and content, but the organisers said growing vegetables and edible plants seemed to be a popular theme this year.
Sandhurst Infant School's "Sandhurst Salad Bar" and the "Tasty Treat Garden" by St Lawrence School, East Molesey, will feature salad leaves, herbs and vegetables.
Other gardens have taken environmentally-friendly ideas as their themes, including features such as recycled newspaper seed pots, bird feeders and even a "bee cafe".
Pupils from Stoughton Infant School, in Guildford, have used deterrents for slugs including slug-repellent plants, eggshells and a "frog hotel".
The winning schools will be announced on the RHS website on Tuesday 26 March.