As a professional gardener the rule is to look like one 'knows what one's doing' at all times. After all, potential customers want to know I won't dig up their prize plants! In practice however, a trial and error approach is more usual. No matter how many gardening books one reads, or how many hours one has spent working with plants, there's always something which will come back to haunt you.
When I first started gardening for a living, I was working for a busy garden maintenance company in Bristol, but before then, I had volunteered on farms and smallholdings, as well as worked on my parents garden as a child, and there were, to be honest, some big gaps in my knowledge! In my first year, I accidentally cut down a climbing rose. A climbing rose, I can hear you say, 'that's not that bad!' But this particular climbing rose had not only been gracing the entire wall of the house of an elderly couple but had also been a silver wedding anniversary gift planted more than twenty years ago. Now completely gone, because I hadn't checked what the 'dead-looking' stem had been attached to. Of course we offered to buy them another rose in case it didn't survive, and of course the gentleman declined, and out of a very English politeness, even had us back! I was mortified, however. So I am asking you to be brave and share your plant-like 'skeletons in the potting shed'.