I'd plant one every six inches, so two rows, ten in a row. Of course
there are many sizes of tulips so spacing can vary. Personally I
prefer to naturalize bulbs, I really don't like them lined up in a
plot like soldiers. In a plot like yours invariably a couple won't
come up so your plot will look like a toothless grin. I'd be more apt
to plant a couple of clumps of like five each, along with a few
different bulbs in clumps, like daffs and hyacynth.
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