Plants need sun, soil, and water to grow, and you need to provide the latter by watering. You’ll be more efficient at watering your plants if you know how to upgrade the irrigation hose in Lightyer Frontier.

To upgrade the irrigation hose, you'll need an upgrade depot, which you can build with aluminum ingots after clearing Pine Heights. The only resource you need for the upgrade is Polyberry Oil, but to get it, you'll need to grow Polyberry plants and press them into oil in an oil press.

To build an Upgrade Depot, you will need to cleanse Pine Heights, which will unlock new resources including Aluminum Rods, which are needed to build. Once you have gathered resources, go to the Build menu and select Upgrade Depot from the Essentials. The recipe for building an Upgrade Depot is as follows:

Once you build an Upgrade Depot, you can dock your Mech and access the command table. What we need is the Mech Upgrade section; look for the upgrades with a water drop icon.