Answer: Dahlias can grow from 1'-6' tall, depending upon variety. If you're growing the large cactus or dinner-plate types, space the plants 18"-24" apart on all sides. Most larger dahlias will need support as they grow so place a 6' stake in the planting hole along with each dahlia tuber. Then, as the stems grow, you can gently tie them to the stake.
If you're growing the smaller border type dahlias, you can place them 12" apart.
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