Root growth rate of frogbit and dwarf water lettuce

[RampageRR]

I originally bought 5 or so plants of each of frogbit and dwarf water lettuce. Fast forward 3 months or so and my entire 6 foot tank has been covered - I am completely fine with this and expected them to grow quickly. However, I'm only seeing 1" to 1.5" of roots hanging down into the water column. My goal was to cover the mid-water level in roots for my exodon shoal to swim/dart in and out of. I'm not seeing any root length at all - does anyone know if there's anything that can be done to grow them out longer rather than have the plants continue to propagate up top?

 

[RampageRR]

This is what I started out with in early March.


This is about a month ago. It's similar to this now but probably 90% top coverage.

 

[Hendre]

If you want proper roots float some Water sprite, I had it back in 2018. Tank is 18" deep for reference

 

[Zanzag]

Agree on the water sprite

 

[Raka]

Water movement is key. Less movement will encourage root growth as they seek out nutrients.

My pleco tank keeps all the roots at less than a half inch with lots and lots of movement. Fiancee's nano tank sponge filter only has 8in long roots across all the frogbit.

 

[mexicatz]

I also believe less water movement should make the roots longer