The oppposite of hothousing is still in the category of gardening.
The opposite of hothousing would be just letting the weeds (and occasional wildflowers) grow, I think. I was the opposite of a hothouser to my yard for a few months this winter, until the landlady drove by and saw the results.
But yes, of course you're right that the whole analogy is ridiculous. The word seems to have been applied to children for the sole purpose of making gifted kids seem unnatural and the result of inappropriate parenting. But as we all know, our kids may be unusual, but that doesn't make them unnatural and their gifts are not the result of our (widely varied) parenting styles.
