How to start begonia tubers indoors right now for a 'vibrant, flower-filled show' all summer

Begonias are a staple of my summer garden. Super-easy to grow and needing very little care and looking after, they add a burst of cheery colour wherever they are planted, whether in containers or borders. So knowing how to start begonia tubers in February for colour later on is an easy win for me and a job that can be tackled now, while there’s not much else going on outdoors.

‘If you want to add a splash of the tropics to your summer garden, February is the time to wake up your begonias,’ says Shelley Davis, plant expert at Flying Flowers. ‘Because these sun-lovers are particularly sensitive to the cold, knowing when to plant begonias is key, and starting them off indoors is essential for a successful season.'

‘While the ground outside is cold and damp, your indoor-started bulbs are safe and steady, preparing for their big summer debut. It’s the ultimate head-start for any gardener, ensuring that when the sun finally breaks through, your outdoor space is already on its way to being a vibrant, flower-filled show.’

1. Know your begonias

,‘Begonias are the perfect solution for shadier spots in the garden, producing masses of rose-like blooms in shades of red, orange, yellow, pink, and white,’ says Julian Palphramand, Head of Plants at British Garden Centres. ‘Both upright and trailing varieties are great for sunny colour, with the latter being particularly valuable for hanging baskets and window boxes where they'll flower continuously throughout summer.’

Tuberous begonias are recognisable by their big, showy flowers with single or double ruffled petals, unlike the compact flowers of smaller-leaved wax begonias (semperflorens), which are fibrous-rooted. Tuberous begonias, with their round, fleshy tubers, are frost-tender and are often planted as annuals each year or dug up for overwintering and then replanted the following spring.

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2. Get tubers started off

'By nestling begonia tubers in shallow compost, the early ‘indoor spring’ allows them to develop strong roots in safety, so they’re ready to be moved into your hanging baskets or garden borders the moment the final frost has passed,’ advises Shelley.

Use a good quality, light, well-draining potting mix like RocketGro Multi-Purpose Compost, £28.99 for two, Amazon, in shallow trays so you can start off a few together. The tubers have a concave side where the shoots will appear and a rounded side where the roots will form. Nestle the tuber (concave side up) in the soil, resisting the urge to bury it deeper, which could result in the tuber prematurely rotting.

Position the tubers roughly an inch apart in the tray. Keep the potting mix moist but not soggy, and avoid getting water in the hollow part of the tuber when watering.

3. Wait for tubers to sprout

Position trays where they’ll receive indirect light and at normal room temperature. After a while, you should see roots developing around the sides of the tuber, while on top, inside the hollow of the tuber, little bumps will start to sprout.

If the tubers seem to be taking a while to sprout, you could invest in a seedling heat mat to get things going a little quicker.

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4. Repot when plants get bigger

Once the tubers begin to sprout and the sprouts are around an inch tall, move them to an area with brighter light or put them underneath grow lights. This will allow them to build stronger stems as they start getting bigger.

When the tubers have two good-sized leaves, transplant them into separate small pots. Bury them a little deeper in the soil this time so that the tuber is covered. This allows the stems and roots to develop, so that they’ll give bushier plants with lots of flowers that will fill out containers and flower beds.

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5. Move plants outside when its warmer

Once all danger of frost has passed is key when it comes to how to grow begonias from tubers. This is usually towards the end of April, beginning of May, and after this, your tubers in pots are safe to move outdoors. Harden off the plants by placing the pots outdoors on nice days and bringing them in at night, which will help acclimatise them.

Once acclimatised, begonias can be transplanted into larger containers or into flower beds and borders. Be careful as you do this, as it is easy to break the stems.

‘Begonias are versatile, easy-to-grow plants ideal for various locations, especially pots, window boxes and hanging baskets,’ says Julian. ‘They flower all summer until the first frost and prefer dappled shade and well-draining soil to avoid leaf burn and waterlogging.’

6. Feed and water regularly

Once begonias are planted outside, treat them like you would any annual flowering plant. Fertilise every two weeks throughout the growing season, using a liquid, all-purpose fertiliser, and then water as needed, at soil level if you can, as overhead watering can damage the blooms and lead to mildew problems.

Tuberous begonias die back naturally each year. Start reducing watering in late summer, and trim yellowing foliage in early autumn. When it comes to how to overwinter begonias, do this before the first frosts, digging up the tubers and gently cleaning off soil before letting them dry on newspaper for a few days. Pop tubers in separate paper bags or wrap individually in newspaper and pack away in a cardboard box, and keep in a dry, frost-free place until you’re ready to replant them again in the spring.

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Will you be growing begonias in your garden this summer? Let us know how you get on.