Nasturtiums prefer lean soil....don't know why they are so wimpy....but I will tell you if you add fertilizer they will, as my grandmother used to say, "go all to leaf". I suspect that they will take off when the weather cools.
Linda C

Lindac is right. Nasturtiums like lean soil. Don't fertilize!

Thanks for your responses. I knew that nasturiums needed lean soil. I'm just wondering what kind of name I should give THIS soil. The garden is new to me. I'm thinking I may have planted in totally used up soil. Have been amending/composting like crazy and getting great results. Hope you're right, Linda, about cooler weather helping - but that won't come for a long time. LOL. How do the nasuriums bloom and thrive in great garden soil. I've seen pics of them planted in vegetable gardens. Very mysterious.

Rosie

All plants need nutrients to stay alive and well, even nasturtiums.
The best is to prepare the soil, feed the soil first.
Nasturtiums do the best in low nitrogen compost.
I sow them in a lot of compost with a little alfalfa meal, kelp + bone meal.
You can tell I do the organic thing. Tons of flowers on healthy plants and they are all in my vegetable garden.
What I would do...work in gently a big handful of compost around each nasturtium plant and keep well watered.
In addition to compost, I use an organic granular fert. that has only a 3% N...keeps leaves a nice healthy green and it does not compromise flower production like the 30%N that is in things like Miracle gro(most of that gets leached from rain and is not a good thing)
Nasturtiums do like cool temps.