Someone had described Walker to me as an "unmissable Euphorbia showman" and they were in no way exaggerating. He talked from 9.30 until 4.30 with about half an hour's break, and was absolutely rivetting the entire time. (He's the jolly-looking one with glasses in the photo, wearing a blue fleece.)

I'm not saying it was for everyone: science dominated, and we spent a lot of time learning about the botany of Euphorbias and learning how they fit into the new Angiosperm Phylogeny, as flowering plants get reclassified according to their DNA fingerprinting, rather than their appearance. For me this was fascinating stuff. (I will understand though, if you beg to differ.)

But it was also great to be able to step out into the gardens, where Euphorbias are a mainstay of almost all the planting. Here, for example (left) are tulips underplanted with E. myrsinites, which makes a spikey grey and green texture that sets off the pink flowers beautifully. And on the right you have E.griffithii giving a great contrast to the frondy grasses, both in colour and in shape.

Walker recommends griffithii for damp soil planting as it does so well next to their pond. A man who can explain botany and give gardening hints, to me is a jewel worth more than rubies.

I also discovered at least four species I'd love to grow that I'd never seen before: E.cornigera is one, pictured left, an elegant pretty red-stemmed plant with those creamy-white leaf veins that look so stylish.

And below right is a Euphorbia so new that it hasn't even been classified yet; all the Euphorbiaphiles fell instantly in love with it, billing and cooing, but the label says merely, and tantalisingly, "Euphorbia sp."

I would highly recommend the courses at Oxford Botanic Garden, which run throughout the year, ranging in subject from very science-y botany to practical gardening and vegetable growing.

Even if you don't find the idea of Euphorbia School tempting, the garden is delicious and well worth a visit, catching a quiet moment amongst its sandstone walls, immaculately-kept glasshouses and riverside setting. And it only costs £3!