First on your question about nutrients, the dirt may or may not sustain the plant. It depends upon what nutrients/minerals are in the dirt, and I would think probably not all of what is needed. Echinodorus (sword) plants are heavy feeders. I have kept them with just the liquid, but with root tabs the improvement is quite considerable. These plants need a lot of macro nutrients and soil may be deficient, depending upon its structure.
On the plant species, some of the cultivars (like Ozelot) do have higher light requirements, especially any with red in the leaves. Mine have not done very well, generally sort of "lasting" for a few months. Whereas my basic green plants like the common sword are huge and thriving, sending out inflorescences (flower stalks, but plants develop from the nodes instead of flowers when grown submersed) two or three times a year with many adventitious plants. When I have removed some of these and planted them, I have even had them grow in small tanks like my 10g. Echinodorus plants have some very interesting characteristics, such as often growing to the tank size and slowly at that. So you might have quite a lovely plant for many months without it getting too large. Trimming outer leaves regularly has been suggested to curtail height, something I have not tried as I've no need to, but it may help. But you will probably have months before this becomes necessary.
I have the basic sword Echinodorus grisebachii var. bleherae in five tanks, ranging from a 20g up to a 90g. There is another "species" that remains much smaller and was originally named Echinodorus amazonicus, but DNA phylogenetic analysis proves it is the exact same species as E. grisebachii (bleherae), so this is more evidence of how the same species can grow to very different sizes. Why this occurs is not yet understood. But I have as I said seen a similar thing with daughter plants from my large swords.
Swords are truly beautiful plants, and very effective in aquaria.
Byron.
