It’s really location dependent. Some places you’ll see the birds in seconds and others never. You’ll need to know the climate, local weather, soil conditions, what else is growing in the area, time of year, etc. to get an accurate answer.

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Stupid Osaka. Birds do not grow.

You’d probably be better off building one of those DIY birds artificially, it takes too long to make natural birds from seed.

Um, acktually they’re government drones, not plants.