I am in the green proffesion p/t and can tell you that tipping is very rare (I've never got one), nor is it expected by any landscaper I know.
You get what you give. Make sure and increase the number and percentage of tips you give to others and I promise you your own reception of tips will increase.
I am given cash tips on about half of my "general labor" jobs (accounts that are not ongoing repeat maintenance jobs).
Rates range from 20 to 50%
My average GL job is about $150 for five hours and it's not unusual to get people paying $200
I think it's partially helpful that I do almost all my work by myself so the end "effort" is more impressive than if the same work was done by two, three or more people.
If I've heard it once, I've heard it hundreds of times in past 20 years - "Wow, you did a great job and you really work hard".
Which I kinda do, though not near as hard as I used to ten years ago since I've learned a lot of time savers and I use better tools today.
But after three, four, five hours when their place is all shaped up and there's like 50 bags of leaves/trimmings piled out front for sanitation pickup, they're very cool about adding a nice tip.