I have a minor in horticulture...major in forestry. It helps with getting people to trust/listen to you. Nothing beats real world experience. Customer relations is most important in my opinion, can not really learn that.
The degree is a necessity for getting the type of customers I want, and keeping them. IMO
I started taking OH classes when I started my business. Best thing I ever did. Id say the best classes were Arboriculture, diseases of ornamentals, pests, and irrigation. Having a good teacher makes the difference.