According to my reading of the iNaturalist documentation, we are supposed to mark things as “wild” if they came up on their own. This would include “garden volunteers”, even if they’re of a species that does not reproduce in the wild in our area. But it does not include wild-type plants that were deliberately planted. It is the establishment means, and not the individual plant’s genotype, that determines the wild field.
There is some gray area between wild and cultivated, with these definitions. For example if I sow seed, that’s probably planted too. What if I merely throw down seed on the ground? What if I shake a seed pod of wind-dispersed seeds (such as milkweed) or open a bag of other wind-dispersed seeds and let the wind blow the seed through a fence, and then the seed comes up on its own the next year? What if I take a stem of a goldenrod or aster, bend it over to touch the ground, and then shake the seed off, and it then comes up in that spot? What if I walk through a patch of white snakeroot and brush against it and the seed blows down onto the ground? The point is there is a continuum between “wild” and “not wild” in terms of whether or not the plant was planted.
In practice, we don’t always know where along this spectrum things lie. But sometimes we have clues.
For example, if there is an annual or biennial plant from a species that does not form seed banks longer than 1-2 years, and you see these plants in an area and you know the planting was done 5 years ago, and the area has not been managed since, then you can safely assume that any plants remaining in the area are wild. Also, if you see a planting in landscaping of a bunch of perennial plants, or trees, in a neat row, and then you see a younger plant of the same species and it is coming up “off the row”, irregularly spaced, it’s safe to assume it was not planted and thus can be marked wild. In many cases, however, it is not clear. For example near me is a planting in landscaping with two northern whitecedars of different age, and then there is a third sapling, kind of irregularly spaced. Could it be offspring of them? Yes. But it could also be planted, and this is likely because I don’t often see seedlings of this species in my area.
When I post a plant where I feel uncertain about its wild status, or the status is in a gray area or there is anything unusual about it, I try to note this in the observation text or the comments. For example if I see something that I am reasonably certain is a volunteer seedling from a cultivated planting, I say: “Seedling from nearby garden / landscaping” or whatever clarification I think is relevant. I think iNaturalist’s official stance though, last time I checked, is that these are to be marked wild.
Personally, I would prefer there were options for more detail, and I would especially like a “not known” field and wish that were the default.