Sandy is correct. The easiest way to handle this is to create categories - think of them as labels or filters, so you can view just the plants in a given category and work on that subset at a time. You can also set a category to private and anything in that category will not be shown (even if it is in other public categories).
On your plant list page, at the top, there should be a link that says "Manage your categories":
That will open a page that lists your existing categories and allows you to add new ones:
Once you have a created some categories, they will appear on the right hand side of your plants list:
You can then add your plants to categories by clicking on the edit button (the pencil icon) on a plant in your list and checking the appropriate category:
Once a category is populated, clicking on it in the list of categories will open the page showing just the plants in that category.
