Answer: Spacing is partly dictated by the ultimate height and width of the plant, the rate of growth and how thick you like to see your plantings. Male ferns grow about 30 inches high and arch gently, so you might put them from 12 inches apart for a lusher look sooner to 30 inches apart for a longer length of time before they need to be divided. The Begonia Wings Mix grows about 12 inches tall in a rounded shape, so for a thick bedding look I would plant them about 9 inches apart; for a barely touching effect about 12 inches apart. The amaranth really need lots of sun so I would plant them about as far apart as their ultimate width to be sure not to crowd them.
Rule of thumb: When you plant two different (or same) plants next to each other, add the width of both together and divide it in half -- that will tell you roughly how far apart to plant them.
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