I know a lot of get impatient when it comes to plants and want to get the best substrate because the plants take off faster. What few realize is that in time, standard gravel, even the epoxy stuff will eventually suport very good plant growth. Although I will never used the epoxy coated stuff again because it is murder in plant roots from sharp edges. Not to mention how tacky it can look.
In my experience with gravel, it takes about 6 months for it to become seeded well enough to support really good growth. And when I say really good, I mean weed rates of growth if you dose properly and have enough light. Root tabs seem to be the key to this. I believe, although I have no evidence of this, that root tabs are the key, mainly the laterite in them. Once you have added enough root tabs in the tank, the laterite becomes sufficient enough to support good growth. Until then you get mediocre growth because of the lack of root nutrients even if you have root tabs right under the roots. I know it is confusing but just seems to work that way.
I also think it has somethng to do with bacteria becomeing colonized in the gravel that assists in the breaking down of nutritents to more useable forms. No, not cycling bacteria but stuff like nitrogen fixing bacteria and other plant beneficial bacteria, assuming there are such things in aquarium environments.
The adding of root tabs and the maturation of the gravel could be linked although I wouldn't have a clue in what way.
I am gonna try to find laterite, I hope that is the right stuff, in a granule form and start a new tank with it mixed in the gravel to see if that helps excellerate the amount of time it takes for my plants to grow like weeds. will let you know if I can find it and if it works.