Ahh, too many voices
Okay, the pearl grass grows at a good clip, not like CO2, but it grows faster than you think.
Maybe like hairgrass in a CO2 tank, about that same speed.
You might try plain old ground peat from the nursery, I hate sphag personally. You could also try some leonardite too.
Barley straw pellets, soil will work well if you soak it 2-3 weeks and then add about 1/2-1".
I soak the peat first. Maybe a day or two.
You can vary the amount of peat etc which I think works better than soil in a non CO2 tank to suit your taste.
I really like onyx over the longer term with non CO2 tanks.
Flourite was/is good also.
I add about 4x the normal amount of peat in a non CO2 vs a CO2 enrcihed tank.
You can dd a number of different organic matter sources.
Leonardite will take longer than peat that will take longer than soil, that will take longer than mulm and detrial materials to decompose.
Peat is right in there. Neil's had a peat tank running for a decade with good consistent growth. No gas.
You "maximize" and maintain the light use efficiency
of your tank.
I think that should be the goal for any plant tank.
That goal is easiest to attain at low to moderate lighting.
But if you want to get everything out of a small amount of light, adding CO2 will help take the pressure off this low light "stress" allowing wonderful growth at lower light levels.
This also means less algae growth and plant growth but still have nice appearing plant growth, just slower.
A shop light over a 55 gal and some flourite and good CO2/nutrients once a week with 50% water and a good sized fish load works very well.
But you could add more light and get more out of it. I'm just giving you some options if you want to improve plant growth besides the obvious addition of more light.