The best time to plant dahlias in New Zealand is generally from early spring, around September to October, once the threat of frost has passed and the soil has warmed up. In warmer regions, planting can start as early as August. Dahlias should be planted when the soil is warm enough, often compared to when tomatoes are ready to be planted. This timing allows dahlias to grow well for summer and autumn blooming. Some sources note that planting can extend up to late December as well, depending on climate and region.