Tuberous Begonias Beginnings

Tuberous Begonias have easy beginnings and great finishes. I grow several of them every year for their great foliage and huge colourful flowers and best of all they thrive in the shade, brightening up my back deck like nothing else can.
Mine have been down in the basement surviving their winter storage and rest period They do need that rest and will not do well if we try to bring them in and keep them growing indoors over the winter. If you don’t have any in the basement then head out to the garden centre, or any of several quality online sources, about mid February and choose a few to start indoors. They need a couple of months indoors to get to a blooming size before going outside after all danger of frost is passed. Compare prices and sizes; bigger is better in Begonias but the fancier varieties will also cost more than some of the old standbys.

When to Start? Tuberous Begonias will actually tell you themselves, sometimes. With no encour-agement they will start to put up little shoots from the concave centre of the dry stored bulbs. If they are a bit reluctant to wake up, then we can encourage them. In early March mine find themselves having a bath. A nice warm, about 43° C , (109° F,) bowl of water with just a touch of bleach is a great way to get them going. The bleach deals with any fungus diseases that may have also been spending the winter in your basement. They should spend about 15 minutes in this bath and then be set out somewhere warm and reasonably well lit. They will eventually put up those first shoots.

How to Start? Only after you have seen those first new shoots should you consider planting these tubers. The shoots should originate in the concave area on the top side of the tuber. To conserve space in your propagation area you can start several of them quite close together in a flat or shallow container. They need a light well drained planting medium because excess moisture is their enemy. Plant them so that they have about 2cm of soil underneath the tubers and another 1cm covering their tops. They make their roots from the top of the tuber and the base of the growing stem. This might leave the tips of the shoots just peeking out of the soil. Water them well, making sure that the excess water drains away. They won’t need any further water until the surface of the soil is getting quite dried out.

Getting Them Growing Your Tuberous Begonias now need some light and some warmth. Mine do quite nicely under the fluorescent lights where all of my seedlings and Geraniums are growing. When they start to produce some good sized leaves they can be fertilized at half strength every second watering. They can continue to grow in these shallow flats until they have made reasonable sized plants, with their leaves starting to touch each other.

Potting Up! When your Tuberous Begonias have reached the size where they need more room you have two choices. The choice is primarily dependent upon the space you have for them. They can be potted directly into the large pots that they will spend the summer in, at least 20 cm (8") pots are needed for a good summer plant. If you cannot keep them indoors in that sized container then put them in pots that will easily hold their root balls, I use about a 10 cm (4") pot and then repot them just before they move outside. When you repot them, bury a bit more of their stems as they will produce roots from the buried stems. Those new roots will make them more sturdy and able to withstand the winds of summer.

Summer Care! Despite the extra roots Tuberous Begonias can still be a bit delicate. There is nothing more devastating than having a tall fat stem with a couple of gorgeous blooms, snap off at the base because of the weight and wind. Staking them certainly helps and putting the stake in when you first plant them in the big pots, makes the job easier and helps to avoid shoving the stake through the actual tuber. Mini tomato cages can be built as well and they will do a great job as they hold up all the branches and disappear into the foliage. Fertilize them regularly throughout the summer and water them only when they start to dry out. Keeping them too moist will only encourage the stems to rot and break off. Later in the summer, powdery mildew will probably find them. Strange as it may seem, I have found a spray of 1 part milk to 9 parts water controls the mildew quite well. Don’t wait until you see that fuzzy white growth, just start spraying after every rain sometime in early August.

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