We used to use Ironite on the lawn to green it up - then I learned that it's high in arsenic and contains lead. That put a stop to that.
I've used aquatic plant fertilizer in pellet form for my pond plants (the ones that are not in pots but rather planted directly in the pond) but it was kind of tricky. I used a piece of paper towel and created little packets of the pellets that I could then just tuck into the gravel near the plants roots. That way it would stay a bit more contained rather than just get dispersed throughout the pond. Then I found some fertilizer that came in tablets - much easier. THEN I learned that you can save a whole lot of money and just buy plain old plant spikes - Jobes makes them - and use those. Same thing, just not the specialty marketing.
@addy1 I've mentioned the steel wool - we got plain old steel wool and put chunks in the gravel near the bog plants. That's an old trick my grandpa taught me that he used in his gardens. My plants got green - not sure if it was the steel wool or just time!
This makes me grateful to be past year one and two when I had to baby my plants! Now they take care of themselves!