Growing Begonias From Tubers
Where to grow your begonias
Begonias grow best in partial shade. They are ideal for pots and hanging baskets. They have fairly brittle stems and heavy flowers, so grow them in a sheltered spot. Flowers will go over very quickly if they’re too hot.
When to plant begonias
Begonia tubers can be started into growth from February onwards in a greenhouse or sunny windowsill if you want to get them started early, otherwise wait until the weather has warmed up around March/April.
How to plant your tubers
Plant your tubers hollow side up about 3cm deep into small individual pots. You don’t need to soak them first. They will germinate at around 18°c and poke their heads up in around 6-8 weeks. As soon as the shoots of the tubers are about 2cm long pot them up in 15cm pots and place them into larger pots as the roots reach the sides of the pot. Harden off the plants before planting them out in the garden in May, when no further frosts are forecast.
Begonia tubers should be spaced about 30cm apart in the garden, but can be planted much closer together in hanging baskets and window boxes. For a single begonia plant, a 15cm pot is the smallest recommended size.
Caring for your plants
Begonias will produce many flowers if they are regularly deadheaded. Feeding them once a week with a high potassium fertiliser (tomato feed is ideal) will extend their growing season.
Watering: Make sure they are watered regularly during the summer and that the soil is not allowed to dry out. Begonias love moisture and will use up quite a lot during the hotter spells in the summer but they will quickly rot if left in pooling water so ensure your ground or pots drain easily.
Staking: Trailing varieties of tuberous begonias are meant to creep, so they do not need staking. Upright begonias, however, can benefit from staking so the flower stems stand tall to make it easier to view the beautiful flowers. When upright varieties are 4 to 6 inches tall, place a narrow bamboo or metal stake in the soil near the main stem. Add more ties to provide ongoing support as the plant grows.
Lifting and storage
Being frost tender the bulbs will perish if left exposed to heavy frosts for more than a few days. Most gardeners lift and store their tubers overwinter for replanting in the spring. Lift your tubers after flowering has finished and the leaves have begun to turn yellow. Depending on when they were planted this could be right up to the first frosts in autumn. Store in a dry, cool (but frost-free) location over the winter. Store in soil that is only a little moist and keep this a little moist over the winter (with irregular watering) to keep the tubers from drying out.