consuming 2-3 harvests per day at what quality level? 8 sims consume in the region of 80-100 food points per day. What plants are you growing? How many sims? The quality must be low unless there are 8 sims otherwise you won't need 2-3 harvests per day even with tomatoes.
If your sims have no gardening badge they have to garden quite alot more than sims with even a bronze badge. good thing the badges aren't too hard to get. Mouthwatering plants will give triple the food points of bland plants with tasty in between. Keep at it and your sims will get better at gardening and will get the gold badge which means that every harvest can be made thriving just before harvest with the talk to plants interaction. thriving plants are mouthwatering better than ok is tasty and bad or worse is bland.
To have to need 2-3 harvests every day you need 8 sims and bland harvests if I recall correctly.
some more numbers
example tomatoes absolute minimum food points per harvest
1 tomato plant harvest = 10 +2 with fertiliser +2 in right season
per harvest ignoring bonuses
1 food point per bland fruit = 10 fp
2 fp per tasty = 20
3 for mouthwatering = 30
3 harvests every day gives
bland = 30
tasty = 60
mouthwatering= 90= roughly what 8 sims eat per day in food points


20 plots is really an excessive number unless you have 8 sims a lot and you really should have harvested fruits coming out your ears