Body & Soul0 min ago
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If the plant is in a container you can plant it any time of the year (keeeping it well watered until established). If the plant is bare-rooted, ie not in a container, I would think late autumn is best, say November, when the soil is still workable but the plant is going dormant for the winter. But as for soil and drainage requirements, I don't grow lavender so can't confidently advise on those points.