'Cambridge Blue' is a Salvia patens.... no other parentage is listed in Betsy Clebsch's book.

Bog Turtle - I used to grow this cultivar, and like you they were started from seed. We now have a different cultivar in the garden. I hate this species. It wouldn't be so bad if the plant had just an average flower, but no, it has to have one of the most beautiful I've seen. The truth is, for me this plant is very difficult to grow. Not enough water and it wilts, too much and it flops over, it is always in trouble. It overwinters on the back porch quite well, and although it often looks close to death, it never quite dies. A few years ago I got tired of all the fuss and exposed my plants to sub-freezing temperatures. They died and I thought I was done with the species. Then the following May my wife comes home with a salvia she's wild about - another Patens.
There's another cultivar I've been hearing about, a giant Patens I think called Guanojato. There may be mention of it at robinssalvia.

Thank you for your quick response. I will keep it for a while until I also become tired of it. I would like a plant with several stems blooming at the same time, but this has not happened. This year I used supposed topsoil from the local MUA in the pot. Useless stuff. Next year I will pot it up in good garden soil, which I do have on my property.

To get the best show from Salvia patens it is best to plant several plants , 5 or more, together.

There are several cultivars of S. patens.

S. patens the species with gentian blue flowers.

S. patens 'Guanajuato' with larger gentian blue flowers than the species. It grows to 4' tall but tends to be lax in habit so grow it where other plants can help support it. It also has a dark spot on the leaves.

S. patens 'Cambridge Blue' with light blue flowers.

S. patens 'White trophy' with white flowers.

S, patens 'Lavender Lady' with lavender flowers.

SG

I have found in the UK, that all forms of S. patens thrive in partial shade. They do require watering in dry spells. They are usually hardy here, but a bit late to sprout in spring. 'Guanajuato' seems to be the least hardy. However, they all seem to come 95% true from seeds, and are easily treated as annuals.

Sometimes a whole plant will suffer die-back for no obvious reason, this also occasionally happens with S. fulgens. Might be a virus or even a fungal disorder. Cut off any wilting stems to the base, and the plant will inevitably recover.

I agree that 'Cambridge Blue' is the best light-blue flowering Salvia. Wouldn't it be just great if there was a large form in this colour, like 'Guanajuato'?

Regards, Robin.