I read in the books that nasturtiums shouldn't be fertizilized because they don't flower, just produce a lot of leaves. However, my nasturtiums just end up looking really really sad. Any tips on how to keep nasturtiums happy?
They definitely do flower. Can't help you on the fertilizer (although I seem to remember that they don't need a lot of it), but if you could post a picture of them maybe someone could tell you what it is that's making them sad (I think other things like improper watering, insects/disease might be more likely than lack of fertilizer)
I don't fertilize mine after planting. Just a little compost worked into the soil in the area where the seeds will be sown. I also don't water them a lot once they germinate. At least in my experience, too much water makes them all leaves and few blooms.