Answer: Annual sweet peas last for such a short while that I like to plant them close together for a very full look, so I space them about six inches apart along the trellis. The perennial sweet pea, however, is a much rangier plant so I would suggest 12 to 18 inches apart for those. Since you are using transplants rather than seeds, you might want to space them a bit closer together. The reason I suggest this is that sweet peas do not always transplant well so you may have some losses.
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