The courses - on 26 July and 30 August - aim to teach participants how to create low-maintenance gardens that will thrive in drought conditions.
The 1.6ha garden is in a frost pocket, a rain shallow area, naturally dry and on sandy soil, making it an ideal base to learn drought-tolerant planting techniques.
"With hosepipe bans affecting much of the country, there has never been a better time to take a fresh look at your individual garden situation and gardening style," said Lucas.
"Visitors to Knoll are frequently surprised by just how little effort is required to have stunning borders all year round."
He added: "I hope that this master class will inspire people to look afresh at their planting schemes and reduce not only the effort they have to put in, but also the amount of water required to create their own spectacular gardens, regardless of the vagaries of the British weather."
Lucas is working on an extension of his gravel garden, which includes grasses such as Pennisetum 'Red Head' and P. villosum, Stipa 'Gold Fontaene', Festuca 'Tomales Bay' and Muhlenbergia rigens. These will be planted with perennials including Gaura 'Whirling Butterflies'.