At this point I think you've made up your mind, but I'll give it one more shot.
Let's work backwards to get where you want to be (quit teaching, do lawn care to provide capital to buy more rental properties).
Monthly Gross $4,167.00
SS & Medicare (319.00)
Union Dues (100.00)
Health Insurance (175.00)
Fed & State Income Taxes (656.00)
Net Pay from Teaching $2,500.00
Current lawn care net 750.00
Total Net Income 3,250.00
Yearly Net Needed 39,000.00
Health Insurance Costs 13,000.00
Retirement at 417/month 5,000.00
Tax Needs 24,000.00
Net Income 81,000.00
SS & Medicare Taxes 12,393.00
Fed & State 12,150.00
Net After Taxes 56,457.00
So let's assume you need to hit around $80,000 in net income to achieve the same income and receive the same benefits that you currently receive.
Assuming an 65% profit margin (not too agressive for a solo operation), you would need to gross $124,000 a year.
Also you probably aren't considering other benefits provided by your job (probably a small life insurance policy as well as disability insurance).
Just some food for thought. Not many solo lawn guys grossing $124,000 a year. Those that do are working twice as hard as what a public school teacher does.
None of this is to discourage you, just trying to point out it is much more difficult than most folks imagine.