I would say this is really a question of how much can you stomach doing things that could be considered against the law so you can save money vs. how many hoops can you afford to jump through to get licensing/certification and is that worth the protection and recognition it affords.
If you plan on just being a small rural business that only works by word of mouth then the less regulated 'under-the-table' business would probably work fine but if you want to become anything larger than a one or two person operation or offer your services to a large amount of basically strangers (including commercial and municipal customers) then you'll need everything to be in full compliance with all your applicable business laws.
Really, the way the system is set up (for better or worse, I didn't get to pick it) if you can handle the logistics of it one of the best ways to go, IMHOO (<- that's In My Highly Opinionated Opinion), is to have a separate entity (LLC or Corp) for each mostly unrelated operation (your operating companies) and a holding corporation that legally owns all those different operations. The operating companies do all the actual work that the business does, whether it's sell trees, make widgets, write code, whatever but don't physically own anything. Every physical thing that the entities need to operate (vehicles, office equipment, buildings, equipment) is actually owned by the holding corporation and leased to the operating companies for exactly
enough to take whatever profits the operating companies have made. As long as this system is implemented properly and run legally the holding company will keep all the money and have almost zero risk exposure while the operating companies carry all the risk but have practically zero assets for anyone to come after in the case that somebody decided to take legal action against the company.
Here's an example: you either have Nursery B or you have Holding Corp and Nursery B supplying trees to a very large commercial operation. It gets proven that the trees supplied weren't quarantined properly and introduced deadly tree virus that wipes out every specimen tree on their site so they sue for tree value replacement costs of 1 million dollars (please read that in Dr Evil's voice). If you're Nursery A with only $10-20K in capital and another $40K in assets, you file bankruptcy, they sell your stuff and take everything (or you have to try to operate a business with the drain of paying back a large settlement for many years), you probably go bust. If your Holding Corp and Nursery B they sue, Nursery B just gives up and says "take everything we have, we're going out of business" but there's no assets there for the courts to take - the courts can't say "we know that your money from Nursery B went to Holding Corp so Holding Corp has to pay" unless you've been committing some kind of fraud, that's the "corporate veil" that protects your money. Now Nursery B is out of business but Holding Corp just forms Nursery C with all the same equipment and employees that Nursery B was using and is only out the money it cost to organize the new Nursery C legal structure.
Hope I did't confuse anyone too much, it can be a tricky subject and I'm just a small business owner trying to figure this stuff out myself.