Hi, I checked your test problem with 2 tables on sqlite db and I see you need a database expert for long-term position.
query; SELECT * FROM moistures WHERE average < ( SELECT MIN(moisture) FROM plants ) ORDER BY id DESC LIMIT 5;
I have good experience in various databases including Mysql, Sqlite, MonogoDB, Redis, Firebase DB, etc.
I am able to work full-time and even I can fit your timezone.
Please ping me to discuss more. Thanks