Any help would be greatly appreciated.

Your first idea would work fine as long as you tip out any excess water from the tray after a couple of hours.

Pigweed will grow in anything so I really wouldn't stress over the mix. Just use what's cheapest.

Is this for an experiment or something?

How deep would you recommend filling the water? It is for an experiment on different natural herbicide solutions to use on pigweed once it grows

really ...not enough facts ....

once germinated..... you should pot up .. to a plant media ...

and once you change media.... you water accordingly ...

you seem to want to choose one media... and go from there ... thats not how it works from there ....
one step at a time ... different rules for each step ....

why pigweed ... lol .. why do you need herbicides????

ken

It doesn't matter how deep the water is since you are going to tip out the excess.

Hello,

I was planning to make adjustments once the plants germinate. I had used potting soil for the germination stage before realizing there were much more suitable options. Since I did use potting soil (77 to 87 percent aged pine bark, sand, and perlite), would you recommend me sticking with that soil for the growing stage or would different soil be optimal? Pigweed is used in a lot of studies on herbicides because it can grow fairly quick as a test subject, and I received seed from a research agronomist. The aim of the project is to demonstrate ways in which weeds can be effectively controlled without the usage of chemicals.