Can i deduct the cost of computer and cell phone repair if I don't have a separate office for my business? i do landscaping, so most work happens on site.

[Opus 17]

Probably not, and no.

Computers and cell phones are "listed property". This is a special status that applies to property that has dual consumer and business use and where deductions are likely to be misused.

With listed property, you can only deduct expenses (such as repairs and calling plans) if you keep a log of your personal and business use and only deduct the percentage of business use. 

 The purchase of listed property is subject to depreciation as with other business assets. It may be a direct expense but not always. Depreciation is subject to certain rules. Additionally, listed property can only be depreciated as a business expense if you have a log that documents the percentage of business use AND the business use must be more than 50%.

The simplest situation is if you have a computer or cell phone that is used only for business and you have a separate computer or cell phone that you use for personal purposes.  Then you can depreciate the purchase of the property and you can deduct your ongoing expenses as business expenses.  If you don't have business only items, then most people do not keep the kinds of records needed to be able to deduct expenses or depreciate the purchase of dual use listed property.

[TaxGuyBill]

Cell phones are no longer Listed Property.

Personally, I would also deduct or depreciate the computer, but use conservative estimates for business use.

[Opus 17]

If cell phones are no longer listed property, then you can  deduct the percentage of your repairs that is the same as the  percentage of business use, and you can depreciate the percentage of the cost that is the same as the percentage of business use without worrying about the 50% limit.  You are still supposed to have a record that allows you to determine the percent of business or personal use.  If you don't have records proving the percentage of business use, then, if you are audited, the result would depend on whether your particular auditor thinks your estimate is reasonable.  Auditors do not have to give you a deduction you can't prove, so it's up to you how much risk you want to take.

[TaxGuyBill]

I missed your comment about 50% business use.

Listed Property CAN be depreciated if under 50% business use.  However, it would need to be depreciated over the longer ADS recovery period and would not qualify for the Special Depreciation Allowance or Section 179.