I grow since many years one pot with P.tetragonum .....it looks never very well ....
In last fall a friend of mine told me that these plants are wintergrowing
I follow his advices and put this plant in winter in my greenhouse and I gave it all 2 weeks a little water ...and it grows and grows .....before some weeks I could see that comes a lot of buds ( more than ever ) and now are lot of flowers open
Pelargonium tetragonum
Hans