Each Expense category in TurboTax Self-employed gives you the opportunity to create line items under it that you can name.
Exactly how you do that depends to some extent on how much detail you need for your own purposes.
You could create a line item called Job Materials under "Supplies" and lump all of those costs together.
If it's more useful to you to have for example multiple pesticides listed, or fertilizers or what have you, that's totally up to you.
Remember, you are only allowed to expense on your tax return what you actually use. If you still have a material amount left over you should reduce your expense and increase inventory.