The Garden Planner is really aimed at the home gardener rather than for commercial use (although we do have farmers who use it and love it!). There are a couple of steps that can help with larger growing areas:
You can create up to 5 plans per year which allows you to split the growing area into several plans. Each plan can be up to 1000 feet (303m) in either direction.
In your plan's Settings, you can edit how plant icons are displayed on your plan. This will speed up scrolling for large plans, since if the Garden Planner has to draw every single vegetable on a very large plan it can slow your device down, especially on older or slower devices.