It is normal for plants to struggle and fade when newly planted. They should be fine in your substrate and will spring to life if light and nutrients are sufficient. Aquatic plants take nutrients mainly from the water column, not through the substrate, and your aqua soil will readily provide the nutrients needed throughout the tank. However, there may be gaps in nutrients (fish will actually help fill many of the gaps).
If you are interested in establishing a planted tank, you should do some testing of your water for NO3, PO4 and GH. These kits are relatively inexpensive. I prefer the Salifert kits for NO3 and PO4 and the API or Sera kits for GH. If you would like to post the results of those tests, when you get them, we can comment upon the nutrients a little better. It may be that some supplemental dosing will help. In the meantime, so long as your tank is fully cycled, it would be good to add some fish. do you have an ammonia reading?
I’m a little concerned about your light, though. A 14-hour photoperiod might be considered excessive, depending upon the light intensity. Too much light, without injected CO2, can harm plants and encourage algae. You may want to dial that back to 6 hours until we can see what you are dealing with in terms of your total setup. It would help for us to know what light you are using. In fact, if you are inclined to provide more info, the following is ideal:
- Light (make & model): ideally, PAR and PUR reading at the substrate and photoperiod?
- CO2 setup (if any) and, if you inject CO2, what is the CO2 ppm level and how is it measured?
- Current NO3, PO4, GH, KH, pH and TDS readings and which test kits are used for each?
- What you are dosing (product and quantity) and how often?
- Substrate type and how long has it been in place?
- What is your filter setup?
- Cleaning regimen (filter and water change frequency and amount)?
- Circulation: surface rippling and are all plants gently moving from top to bottom?
- What is your water source and do you use a water softener?
- What is your tank size?
I think that what you are doing is establishing what is called a low-tech setup (no injected CO2 and - maybe - low light). If so, you can do some research on setting up a low-tech system here on TPT. There are many journals that will give you examples of such setups. Just search “low tech journal” and you will see many examples.