Answer: I'm afraid the nursery was right - spirea can grow larger than you want, but you can prune them annually to keep them smaller. If this sounds like more work than you're willing to invest, why not plant some smaller plants? Heathers remain about 3' all around for many years (although occasional pruning will keep them smaller). Lavender is another mounding plant that rarely exceeds 2'. Rosemary is another mounding shrub that might work for you. Hope one of these suggestions is just right for your garden.
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