(from the book of Cereus, Chapter 3, verses 1-10)
3 1 Thou shalt water thy plants when and only when they require water, eschewing the calendars of man.
2 Thou shalt learn the signs of the plagues of insects (and arthropods)a I will send against thee, and be watchful against them, lest they overtake your plant.
3 Thou shalt not plant thy plants in a pot lacking drainage: it is an abomination, saith the LORD.
4 Thou shalt not cause thy plants to stand in drainage water.
5 Thou shalt learn the names of thy plants.
6 Thou shalt water thoroughly, until water saturates all of the soil in the pot.
7 Thou shalt not plant thy houseplants in topsoil or garden soil.
8 Thou shalt not give fertilizer to an ailing plant, nor too much fertilizer to a healthy one.
9 Thou shalt not covet or steal cuttings from thy neighbors, nor from public spaces, nor from any other plant which does not belong to you.
10 Thou shalt share cuttings with thy neighbors as with thyself.
a Some manuscripts do not contain (and arthropods).
These are arranged in approximate order of how often they're broken by the people who come in to work, or call with a question, or post at Garden Web. Most common errors at the top, least common ones at the bottom. At least, more or less. It's not like I count. Though maybe I should.
If pressed, I could come up with many more (as, please note, did Moses: the actual Ten Commandments starts out Exodus 20, but then he spends Chapters 21-22, most of 23, 25-30, and most of 31 on various rules and laws and instructions, some of which are still relevant and sensible -- Exodus 22:21 and 23:7 are personal faves -- and others of which are less applicable to 21st Century America. Like e.g. Exodus 22:16-17. I'm just saying.), as there are a ton of other things people do wrong. But, you know, ten is a nice round number, and one has to stop somewhere. I'd be willing to drop 9 and 10 if somebody has some better suggestions.
I've personally, at some point in my life, broken all of these except #7 (though #5 was involuntary), and especially #9 (mostly with the coveting, not the stealing). Recently, only 3, 4, 5 (still involuntary), and 9.
Those of you who were hoping for the Sermon on the Mount ("Blessed are the Dieffenbachias, for theirs is the understory of Heaven") will just have to keep waiting.
If anyone was curious: the opening picture is from Hope Lutheran Church in Germanville, IA (which may or may not be an actual incorporated town: I was always confused on this point as a kid, and thirty years have not clarified anything for me. But it is listed on Google Maps.), which is the actual church that my parents and I attended from the time I was about two to maybe eight years old. The above picture is almost exactly how it looked then, too: I think the TV is the only addition in the last twenty years.