But what does grow on trees? Take apples, for example.
In order for there to be apples (at least ones that you would want to eat), there's a whole lot of work that had to happen. An orchardist had to plant the trees, then tend them, prune them, take some sort of measures for pest control—and wait a few years before there was any fruit as payment for his labors. Not only that, there had to be appropriate physical conditions: the right sunlight, moisture and temperature, and the right nutrients in the soil (or else additional work to add the nutrients and supply the water).
In other words, things that grow on trees have a physical reality, and so, like the rest of the physical economy, they depend on some mix of natural endowment and human labor.
In contrast to money, which can be produced with no physical work at all and free from any dependence on favorable physical conditions. As I’ve discussed elsewhere, money is a social construct—it is whatever we agree it is—and it can, in principle, be called into being by nothing more than a credible promise.
From this perspective it’s odd that we say “money doesn’t grow on trees” to mean that money is hard to come by, when in fact it’s easier to produce than things that do grow on trees.
But of course I’m playing fast and loose here. A society may be able to create money out of wholecloth (or not even that—out of nothing more than electrons in a computer file), but that’s not possible for an individual or a household. And the difficulty of money compared to apples would have been felt all the more keenly in an agrarian society.
The typical American household today produces almost nothing of what it consumes. Amateur carpenters, knitters, and potters still buy their wood, their yarn, their clay and fuel. Even most vegetable gardeners produce only a small fraction of their annual diet. Home production is at most a marginal activity for all but a few households. We do some kind of work, generally unrelated to what we consume, and in exchange we receive payment in money, which we then use to buy what we consume. And so we naturally think of our income as money, rather than seeing our income as the service or physical product that results from the work we do.
But they would also want things not produced in the local economy: a dress that’s beyond the abilities of the farmwife or even the local tailor; a cookstove; a farm implement that’s more complicated than the blacksmith can make. For all those things, they’d need money—not just scrip from the local bank, but money money, stuff that will be recognized in Chicago or New York. And that sort of money was probably hard to come by in the rural economy. It wasn’t enough to produce something. You had to find someone who had money, and you had to hope that they were willing to part with it for what you were able to produce, at a price that didn’t make you feel like you were getting ripped off. I can see how that would look like a chancier proposition, something less under your control than going out in your field and producing income.
So you had to be very thoughtful about what things you bought and careful about buying any “frivolities” from beyond your local community. After all, money doesn’t grow on trees, you know.