Hey brain trust how are we on this cool sunday of 36 degree heat...
Ok I've done a 30min kids planter box project at home using scrap wood from my last project. What im wondering is this... do planter box that sit off the ground need drainage holes? Ive lined the inside with black plastic and tried to seal it as much as i can so it retains water more so, as i know boxes like these do dry out fast. Or is this more of a management of how much water goes in. Dimensions of the box is 1160L x 450W x 180H and inside is lined with black plastic
What a fantastic planter box you've created there @Dark!
Will you be placing this unit out in the weather? If so, you might experience issues with it filling up with rainwater and becoming a pond. Drainage holes will be needed to prevent this.
If it is going to live undercover, then you could turn it into a wicking bed system. You'd start by filling the bottom 5cm with aggregate and covering it with drain matting. Holes can be cut in the drain matting, and a natural fibre rope pushed through them. The rope allows the water to be drawn up out of the reservoir and into the soil. You still need to pay attention to not overwatering, and a hole placed on the side 5cm from the bottom will allow excess water to overflow. I've drawn a rough image below to illustrate.
Please let me know if you have further questions or need assistance.