Bishop Dahlia in May: monthly care

Bishop of Llandaff dahlias are grown from tubers, not true bulbs, and must be planted after all risk of frost has passed. In temperate Europe, April and May are the ideal months, once soil temperatures have warmed to at least 10°C. Choose a position in full sun with shelter from strong winds, as the tall stems can reach 80–110 cm and may snap in exposed sites. Soil preparation is critical. Dahlias thrive in fertile, well-drained loam or sandy soil. Dig over the planting area to a spade's depth and incorporate plenty of well-rotted compost or manure a few weeks before planting. Avoid heavy clay that stays waterlogged, as tubers will rot. If your soil is heavy, work in horticultural grit to improve drainage. Plant tubers horizontally about 10–12 cm deep with the old stem or "eye" (the growing point) facing upwards. Space them 50 cm apart to allow for their mature spread of 40–60 cm and good air circulation, which helps prevent fungal diseases. If you're planting in rows, keep at least 50 cm between plants in all directions. Insert a sturdy bamboo cane or support stake at planting time, positioning it a few centimetres from the tuber to avoid piercing it later when roots have developed. Water the tubers in lightly after planting, but don't saturate the soil—tubers can rot if kept too wet before shoots emerge. Once growth appears, water more regularly. A 5 cm layer of mulch around the base will suppress weeds and retain moisture through summer.

Bishop of Llandaff has moderate water needs. During active growth from late spring through summer, water regularly—typically once or twice a week in dry spells—to keep the soil evenly moist but never waterlogged. Dahlias are prone to powdery mildew if foliage stays wet, so water at the base rather than overhead, ideally in the morning. In autumn, as flowering slows, reduce watering frequency. Feeding is essential for strong growth and abundant blooms. Once shoots emerge in May, apply a balanced general-purpose fertiliser. Switch to a high-potassium tomato feed in June and July to promote flowering; apply every two weeks according to the manufacturer's instructions. Stop feeding by late August to allow stems to harden before winter. Maintain a 5 cm layer of organic mulch around the base throughout the growing season to conserve moisture and suppress weeds, but keep it clear of the stems to prevent rot. Slugs and snails are the main enemy, especially when shoots first emerge in spring. Use organic pellets, beer traps, or patrol at dusk. Earwigs can damage flowers; trap them in upturned pots stuffed with straw placed on canes. Aphids may cluster on young growth—squash by hand or spray with soapy water. Powdery mildew can appear in dry summers; ensure good spacing and avoid overhead watering. In zone 8a and colder, lift tubers after the first frosts and store as described in the pruning section. In milder coastal gardens, you may leave tubers in situ under a 15 cm layer of mulch, though lifting is safer in wet winters.