In short, tax deductible are items that have one use or a short use, i.e. office supplies, gas, oil, etc. Depreciable items are usually things that have a usable life of a year or more, i.e. mowers, vehicles, etc. And as monkey said, call an accountant.
Call an accountant. Beyond that, write offs are usually the small ticket items. Larger cost items must be capitolized and depreciated. However, most depreciable items can be written off all at once with a 179 expense (except for 'listed items').
Unless you're going to take the time to read the tax code, call an accountant.