getting relationships right

working on a crop planning database and want to set up right.

trying to insert an image, but can't get it to work (tried .jpg, .png, .pdf!???)

Anyhow, here are a few of my tables

crop info
name of crop (eg. basil)
season
start date
other details

seed inventory
name of crop ("basil" pulled from crop info)
crop variety (eg. thai)
no. of seeds.
etc.

and now I want to create a crop plan from my inventory, and I think (am not sure) that it makes sense to make this into a different table. My problem is I don't know how to structure it to link the crop plan to the inventory.

From within the crop plan table, I've created a table relationship. Then, I've created the following fields:

variety: where I enter in the variety. the problem is not all crops have varieties so if I lookup with this key field, it doesn't work. AND when I click on this, I don't see the "crop info" value in the popup (record) slider

crop name: a formula which enters the crop name based on variety.

Do I need a join table? If so how is that done?

Thanks in advance.