Been There Done That and that is how I got started in Application. Now that is all I do. But it is a good move that puts you in a totally different class as a Full service company. It will give you that one stop shopping that upscale clients want.
Stay away from Rent-A-License. If you are going to have success you need an experienced Tech. Hopefully a CPO. But you need to come out of the chute in high gear letting your customer know they are getting great service. BTW That is the easiest way to build a Lawn Route. Word of Mouth.
Cost wise any time you expand into an other area you are going into Negative cash flow. Pesticide License and Insurance requirements aren't bad. Equipment cost can vary, start with basics. But the Real cost will your CPO Spray Tech. Average Spray Route guys for the Big Boys are making $ 30 to 35K at most. A good CPOIC is $ 50 K Minimum. 100% of your customer base is not going to switch to you. Your Fert & Squirt chemical costs and over head etc. not counting employee pay should be of sales 50%. So there are the basic number for you to consider. Good Luck.
You can lead a Donkey to water but you can't make the Jackass Drink
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"Life is tough, but it's tougher when you're stupid.” John Wayne.