Please tell me that was a typo
If this is a short term situation e.g. the cable guy is coming next week, you could use a temporary mobile hotspot to set up a fixed schedule that assures you of adequate watering.
For longer term (you’re house poor and won’t have home broadband for a while), perhaps you could ask a neighbor (if signal strength is adequate) to let you use theirs for just this application; bandwidth usage is negligible.
If this is really long term (you don’t want Wi-Fi in the house because the kids abuse it) I believe you can enable Wi-Fi, set Rachio up, then configure the router to stop broadcasting the SSID. Rachio will remain connected and the kids won’t know it’s there.