1. Soil - although VFTs come potted in sphagnum, it really isn't a good
medium. A better mix is 2/1 peat/sand mix. Use a coarse quartz sand.
It is good to give them a little more room than they have in these little
commercial pots they come in too -- I use a 4" diam., deep pot., or
larger for several plants.
2. Watering - you are doing okay; watering from above doesn't hurt. Only
this time of year, VFTs are going dormant, so you don't want the pot
standing in water in the winter. It should be kept just moist and
preferably cool, but not freezing. Rainwater or distilled water is
best. Tap water is usually alkaline, and the plants don't appreciate
it. I don't have trouble on the short term, but my plants get "flushed"
by the generous spring rains we have here in seattle. When I water with
the hose, I run lots of water through the pots every few weeks to keep
minerals from building up in the soil. (Our water here is naturally
acid; but they add lime to it so that the city's pipes will not corrode).
3. Fertilization - don't fertilize. Some growers use an occasional
foliar feeding of *very* weak fertilizer, but it isn't necessary. These
are plants native to bogs with almost no available nitrogen, and nitrogen
in fertilizer will rot the roots. Live insects are really the best; you
can grow them outside set in water, and they will catch plenty of
insects. (In Delaware, your summers are plenty humid for it.)
The black leaves: It is normal for some leaves (the oldest ones) to turn
black eventually. Keep them trimmed off to avoid fungus. In the summer
they will be replaced with new ones. In winter, they won't; you will get
a few small leaves, often with no well-developed trap.
Dormancy: These plants, to do well, need a winter resting period. In
the Fall, the growth will slow, and at this point the plant should be
removed from the water and kept just moist. Wet soil can promote rot.
Keep them clean, cutting off dead growth. A spray of a benomyl solution
doesn't hurt either. In the spring, when growth resumes, place in water.
You should consider joining the International Carniverous Plants Society
and get their quarterly newsletter, as well as looking up local growers
(there are bound to be some). Also, either of the two books by Adrian
Slack are very good.
Good luck!