General
Dahlias are tender perennial plants grown for their spectacular, long-lasting blooms in an extraordinary range of colors, sizes, and flower forms. Originating from Mexico and Central America, they thrive in warmth and sunshine. In colder climates, dahlias are grown as seasonal ornamentals, with tubers lifted and stored over winter. Their rapid growth and continuous flowering make them a centerpiece in summer borders and an outstanding cut flower.
Light
Full sun; at least 6–8 hours of direct sunlight for best flowering.
Soil type
Deep, fertile, well-drained loam enriched with organic matter.
Water requirement
Medium; water deeply and regularly, but avoid waterlogging.
Nutrient requirement
Medium to high; needs steady nutrition for continuous flowering.
Precultivation
Tubers can be pre-sprouted indoors to speed up flowering. Place them in shallow containers with lightly moist potting mix, ensuring the growing eye is above the soil surface. Keep in bright light and moderate warmth. Seed propagation is possible but mainly used for breeding, as seedlings do not come true to type.
Planting
Plant outdoors only after frost risk has passed and soil temperature exceeds 10°C. Choose a sunny, sheltered location. Space plants 40–70 cm apart depending on variety. Insert stakes at planting to avoid root damage later. Mulch lightly once soil has warmed.
Pruning
Pinch young plants to promote branching. Remove spent flowers promptly by cutting back to a leaf pair. For exhibition blooms, side buds can be removed to direct energy into a single large flower.
Maintenance
Water consistently, especially during dry spells. Feed every 1–2 weeks with a bloom-focused fertilizer. Avoid high nitrogen, which promotes foliage at the expense of flowers. Monitor for pests such as slugs, aphids, and earwigs. Provide good air circulation to reduce disease risk.
Harvest
Flowers are best harvested early in the morning or evening when fully open. Cut long stems and place immediately in water. Dahlias do not open after cutting, so harvest at peak bloom.
Common issues
Slugs and snails damage young shoots. Powdery mildew can occur late in the season. Stem rot may develop in poorly drained soils. Frost kills foliage quickly.
Pollination
Insect-pollinated; bees and other pollinators visit single-flowered types readily.
Companion plants
Cosmos, zinnia, ornamental grasses, marigold, salvia.
Incompatible plants
Plants requiring very dry soil or heavy shade.
