Tropaeolum speciosum comes from Chile where it grows on mountains and mountain valleys. More than soil type, habitat and growing conditions are important.
It comes from humid areas with almost constant rainfall but short dry periods are possible (generally not longer than 1 month).

For light, it grows on level areas or slopes facing north. It likes some shadow and some protection against direct sunlight, some shadow from vegetation, filtering about 20 - 40 % of light.
It grows also on steep slopes facing south or a vegetation cover which filters 40 - 80 % of light.

I'd say as it likes mountainous conditions, improve the planting spot with lots of grit so you have good drainage (best with almost anything other than bog plants) , but then pay attention to the other environmental factors like shading.

Good luck with this plant; it's very beautiful. Let us know on GOY how you get on.

Despite its delicate appearance the best areas I ve seen it grow areas Bertiefox describes ..almost mountainous in places like Scotland Northumberland and North York moors.

Berties details include lots of grit and I d second that as they spread by tubers and may find heavy clay difficult to penetrate and not enjoy the clogging and drying effect clay can produce.That said the acidic nature of clay should suit them.

If interested there are Pics of a beautiful example growing high on North York moors at a beautiful little nursery called Poets cottage at Lealholm nr Whitby.

If you search under Lealholm nursery then go to blog page scoll down to July under heading Our Troppies you ll see some wonderful examples.