If a scientist wanted to study how often a plant needs water, what would the best wat to investigate it?

If a scientist wanted to study how often a plant needs water, what would the best way to investigate it?

The scientist needs to carry out planting in two phases whereby one will be irrigated while the other one will not be irrigated. Observations will be recorded after every few days as regards their height, leaf coloration, stem elongation, among other features will be measured in order arrive at a conclusion

Explanation:

it cools slower in the earth meaning the crystals have more time to form than lava on the surface