Once there are roots, it is safe to start feeding a plant starter formula. You may inhibit rooting if the cuttings are not yet rooted.

Hummersteve:
I use a spray bottle to mist the cuttings.Everything
that I use is organic so don't have to worry about burning.
My mix uses a 6-12-6 fertilizer(which builds a healthy root system) and a liquid rooting hormone called superthrive.
That is very effective on many Salvias too. I usually
put my cuttings in a diluted solution while they are waiting
to be stuck.Your Cuphea is going to need some pinching to
help w/ branching.What type plant food are you using ?
Art

Warmth is another issue. Because I do my cuttings in the basement in winter where it is relatively cool they get bottom heat and get covered at first by the oldest sheet of plastic rap still in use. The problem at this time of year is getting healthy shoots for cutting. For me it means bringing plants out of cold storage on the porch, feeding them and putting them under lights. It usually takes less than a month to bring those plants to cutting stage. I can't speak for shumannii since I haven't tried it, but based on your head start, through a succession of cuttings you could have enough for a yard full by May.
Some Cuphea are amazingly easy to root. With bottom heat David Verity can root in a week. It is the kind of plant to give a grower the confidence to try harder types.

Ward-- You are correct in everything you have said. Warmth not being a problem since mine are inside. I could easily have a yardfull since the cupheas are so easy to root. The shumannii seem to be even more hardy than david verity. As you have said this trial run will give me confidence toward any salvia cuttings I may try later on. I may have to give some of these away.

Art-- I also use a spray bottle while they are in the cutting mix and I dont use anything but water during that period ,except I do use rooting hormone. But once they are stablized in soil I have been using Peters specialties 12-36-14 at 1/2tsp per gal. I may need to back off on that and you are right I will need to do some pinching to force more branching. I have used superthrive but really couldnt tell it did anything. I do use rooting hormone on the cuttings though.

Art--- Have you ever heard of or used Byron's famous tea recipe? I use it on all my seeds and cuttings, so much so now that I dont really think much about I just do it. Supposedly it also helps keep away dampoff.

Here is a link that might be useful: byrons famous tea recipe

Thanks for the link to the Tea Recipe. I will use it
on my salvias too.
Art

Art-- I hope you knew I didnt mean to say I use the tea on cuttings , I meant to say -- I use it on all my seeds and seedlings.