Dahlias are among the most spectacular summer flowers, prized for their bold colours and dramatic forms. But in May, they’re still in their early stages—and what you do now will make all the difference to their success later in the season.
Whether you’re growing them for borders, pots, or cutting, here’s how to give your dahlias the best start this month.
1. Planting Tubers Outdoors
In most areas of the UK, late May is the time to plant dahlia tubers directly into the ground. Wait until all risk of frost has passed—usually mid to late May, depending on your location. Choose a sunny, sheltered spot with rich, well-draining soil.
- Dig a hole around 15cm (6″) deep.
- Lay the tuber flat with the stem or growing shoot facing up.
- Cover with soil and water well.
Tip: If you live in a colder area or have heavy soil, start tubers off in pots under cover earlier in spring and plant them out once shoots are 10–15cm tall.
2. Pinch Out for Bushier Growth
If your dahlias are already growing—either in pots or from early plantings—pinch out the growing tips when they reach about 30cm tall. Simply remove the top pair of leaves with your fingers or snips.
This encourages more side shoots, giving you a bushier plant and more flower stems later on.
3. Support Early
Dahlias can grow tall and top-heavy. Get ahead of the game by putting in support stakes or rings now, before plants become large and brittle. This saves damage later and keeps everything tidy.
Use bamboo canes, pea sticks, or purpose-made supports and tie stems loosely with soft twine as they grow.
4. Water and Feed
Once dahlias are planted or established, they’ll need regular watering, especially in dry weather. Focus on the roots and avoid splashing the foliage to reduce the risk of mildew.
Feed weekly with a balanced liquid fertiliser once plants are actively growing, switching to a high-potash feed (like tomato fertiliser) as buds begin to form.
5. Watch for Slugs and Snails
Young dahlia shoots are a favourite snack for slugs and snails. Use wildlife-safe methods to protect your plants—like copper rings, beer traps, or wool pellets—and check regularly for damage, especially after rain.
At a Glance: May Dahlia Tasks
- Plant tubers outdoors after last frost
- Pinch out growing tips for bushy plants
- Install supports early
- Water and feed regularly
- Protect from slugs and snails
Looking Ahead: By the end of May, your dahlias should be established and growing strongly. Keep them well-fed, supported, and watered, and you’ll be rewarded with a stunning display from midsummer right through to the first frosts.
