When it comes to tipping landscapers, the general rule is that you don't have to. This is because these skilled merchants typically work for themselves, and large companies that can ban tips. Furthermore, labor costs in the landscaping industry are already quite high, so there is no need to tip as they are adequately compensated for their efforts. That being said, if you feel that the job was done exceptionally well and you would like to show your appreciation, then you can certainly tip them. However, it is important to note that this is not expected or common in the industry.
If you do decide to tip your landscaper, it is best to give them cash. This way, they can use it however they please and don't have to worry about any taxes or fees associated with other forms of payment.