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human
[Dragonball Z] Why are there never enough Senzu Beans?

It seems that every time the Z fighters need a Senzu Bean, there is a severe shortage of them, but when they conveniently need a new bag of beans, they can get them dead easily.

For example: They had a full bag of Senzu Beans when they fought Android 19 and 20 and it was apparently a big deal that they had them. They then have another full bag of beans when fighting Cell in the Cell Games, which was arguably less than a month later? Not to mention that they had a full three years to prepare for The Androids, so Korin should have been growing those beans like a champ!

Also, when they're fighting Cell and he steals the Senzu Beans, they think it's all a big shock. Goku has instant transmission, so why the hell didn't he just teleport to Korin's tower and get some more? 

Fast forward a further seven years and they're still running into the same problem of running out of beans. Korin had seven years to stock up on beans! He should have entire closets full of them, and yet he always gives out a tiny little bag with barely any beans. 

Throughout the Buu Saga, there were only two situations where Senzu Beans were used. Videl gets one and Majin Vegeta gets the other, with the understanding that there are no other beans. What the hell, Korin? What have you been doing in seven years that makes it so you only have two beans? 

The same applies in the Saiyan Saga when Goku gets back from being dead and gets some beans from Korin. He eats one to get his strength back and then realizes he only has one left? Why the hell did Korin only give him two beans?

So why is it that there are supposedly so few beans available that they're a valuable resource, but it's clearly possible to grow a whole bag full in less than a month?
gpt
Yajirobe and Korin eat the beans as their main source of nutrition. They tend not to set aside any in times of peace. Korin had a stockpile from the androids preparing for the androids, but was not prepared for Buu. Also, the entire Buu saga happens over only a few days iirc.