You’re watering your dahlia tubers wrong — here’s how to avoid rotten tubers, according to garden experts

That's right — there's a right way and a wrong way to water freshly potted dahlia tubers, and there's a good chance that a lot of us have been making the same mistake.

If you’re planning on learning how to plant dahlia tubers for the first time this year, or you've had no luck with them before, you’ll want one of Sarah Raven's golden rules for growing dahlias under your belt. She says we should be watering freshly planted tubers sparingly (if at all) until they develop into established young plants.

We thought we’d hone in on this tip because apparently, it’s key to avoiding tuber rot — so, we spoke to a panel of gardening experts to find out why watering (or a lack of it) is so crucial in the early stages of dahlia growth.

Sarah Raven

Sarah’s love of gardening extends to all areas, from growing cut flowers and delicious vegetables from seed, to designing stunning gardens packed full of variety, colour, and scent. Always with a focus on helping the environment and biodiversity, Sarah’s gardens are havens for birds, bees, and other pollinators. Her popular gardening podcast ‘grow, cook, eat, arrange’ has achieved 4.3 million downloads. She’s published 14 books and runs sarahraven.com, which services over 600,000 customers.

Above all else, dahlias are susceptible to tuber rot if they're left to sit in wet soil. Sarah says that in tuber form, without leaf, they’re not photosynthesising, which means there’s nowhere for the water to go — and watering simply waterlogs the tubers instead.

‘When in full growth, dahlias are hungry, thirsty plants, but it’s important to go easy on watering at first,’ explain Becky Crowley and Dickon Harding from Raby Castle, Park and Gardens. ‘Overwatering while the tubers are just waking up can lead to rot.’

Becky Crowley

Becky Crowley is assistant head gardener at Raby Castle, Park and Gardens and is working alongside the team there to ensure the vision of world-renowned garden designer, Luciano Giubbilei, is fulfilled in the remodelled Walled Gardens.

Sarah says you should water your pots once after planting the tubers, but after that, you shouldn’t give them any water until growth appears — ‘a decent set of leaves,’ to be exact.

‘At first, you should water your dahlias sparingly, and this can be gradually increased as the plants begin to grow,’ agrees Graham Smith MCIHort, gardening expert at LBS Horticulture.

‘Dahlias in containers will need to be watered much more frequently than those in the ground, but avoid excessive watering in their early stages, as the tubers can rot if they’re left in saturated soil.’

So, when can we start to ramp up the watering?

‘Wait until the soil is very dry before watering, and after the tubers have formed roots and are well established, you can water them consistently in dry periods,’ advises Graham.

Sarah agrees, noting that even after leaves appear, you should only be watering your dahlias once a week.

Where to buy dahlia tubers

• Sarah Raven: Browse a beautiful selection of dahlia tubers.
• Thompson & Morgan: Another dazzling range of dahlia tubers to choose from.
• Amazon: Even more dahlia tubers to shop.

And just like that, you’ve got your dahlias off to a strong start! No rot, and fresh, healthy growth. Whether you'll be potting up dahlias to plant in the ground later in the year or learning how to grow dahlias in pots for the rest of the growing season, avoiding this dahlia watering mistake will boost your chances of abundant blooms come summer.