How Many Vallisneria Gigantae to Line the Back of a 40B?

I want to do valls in my next tank build which will be either a 40B or a 20 gallon high. I have plant plans for the 20, but I am completely lost when it comes to the 40B's aquascaping.
Any thoughts on how many vallisneria gigantae I will need to line the back of a 40B?

 

Gigantae has thick leaves so one plant can cover a lot of area. I have maybe 8 plants in my 90g. It covers about 1/4 the tank but has a big impression.



So to line the back of a 40B, i'd say maybe 20 plants would do er

 

angelcraze .... I thought yours were Val gangsters sorry for the hijack OP I couldn’t resist

 

It was val gangsta i'll never live that one down!

 

I started out with 4 and I now have to regularly chuck new growth.. If you start with 2 or so and let it take hold and send runners you can cut the runners once they are fairly large and replant.

 

I started out with 4 and I now have to regularly chuck new growth.. If you start with 2 or so and let it take hold and send runners you can cut the runners once they are fairly large and replant.

How long does it take for the new growth to grow to say, 6 inches?

 

Once they take hold I would say maybe a week tops. By 6 inches the runner should have already made at least one more runner.