I planted store-bought tomato seedlings in pots three weeks ago. They
have begun to produce flowers now. Should I side dress them now with
nitrogen and bone meal? Originally they had no nitrogen mixed into the
potting mix.
Zone 9 in Houston, TX.

Side dressing at this stage would be appropriate.. no need to over-do
though. What does that mean? Well, yeah, exactly..! How big/tall
are they? If they ae small-ish plants, err on the side of caution.
If large, healthy plants, still no need to over-do.