The account plan - Free or Pro - decides which features are available. New accounts are on Free by default; a working farm is on Pro.
On Free every Pro feature is VISIBLE but inactive (greyed out, with a Pro mark): you can see it but cannot use it. Ordinary (free) elements work as always.
What is available on Free:
the variety catalogue - a curated set, cloned at sign-up; your own varieties can be created and edited;
factory box types - all of them are available for building boxes;
one trial of the editor of your own box types (see Warnings).
What is on Pro only:
the editor of your own box types (creating, editing, deleting, copying a factory one);
the extended (Pro) fields and filters of the variety card - crop, type, breeder, resistances, days to maturity, series and traits, where to buy;
the full variety catalogue;
adding farm members.
When you try an unavailable action, the server refuses and says that the feature is available on the Pro plan.
The editor of your own box types on Free is ONE trial for the whole plan: the first own type can be created, and after saving the editor becomes unavailable. The box you created stays in use, but it cannot be opened in the editor again.
The «In use» switch on your own box type stays available on Free - that is a working state, not editing.
The Pro fields of the variety card are shown greyed out on Free both in view and in the editor (they cannot be opened or pressed); editing the ordinary fields and the notes stays available.
Downgrade from Pro to Free: everything already created - your own box types, varieties, added members - stays and keeps working, but new Pro actions are unavailable and the Pro editors close. After a downgrade you see exactly what someone who has never been on Pro sees.