There was a time when the average gardener thought they couldn’t grow tuberous begonias.
Anyone who visited a flower show last season almost anywhere in the country can tell you about the gorgeous home-grown tuberous begonia bulbs they saw among the winners.
Although growth requirements of tuberous begonias haven’t changed appreciably, some flower gardeners have decided that these spectacular flowers are well worth a little pampering.
For Good Growth Tuberous Begonias Need?
Tuberous begonias grow best in a cool, partially shaded area. They also need free air circulation. Where can you find such an area?
If your garden has a northern exposure which receives some morning and late afternoon sun it will make a good planting place. The north or northeast foundation planting which receives light and is not heavily shaded makes a good growing area. Patios and lath houses where begonias receive filtered light and protection from wind make ideal planting places.
These begonias need shallow planting because they send roots from the top and sides of the tubers. Once growth has started the planting should never be allowed to become dry. These plants enjoy humidity. You can heighten humidity by spraying the leaves during hot weather.
Starting Tuberous Begonia Tubers
If you want your tuberous begonia plants to flower in May, start tubers in January. In Minnesota, they usually start tubers indoors in March and expect them to bloom in July.
Authorities differ on the recommended procedure for starting tubers. Some say the tubers should show sprouts before being planted in the starting medium. Other professional growers advise us to start the tubers indoors by planting them directly into shallow flats or trays of peat moss and sand.
I’ve had good results both ways. If you plant an unsprouted tuber keep the starting medium on the dry side until the tuber sprouts. This forestalls possible rot.
After planting them you can start them at a cool, light window or in the basement under fluorescent lights. When sprouts show, water the planting to encourage good root growth. Tubers are ready for potting when sprouts are four to five inches high.
Potting Begonia Tubers
There are many soil formulas for growing tuberous begonias. If you want to experiment I suggest you consult a book on Tuberous Begonias. For practical purposes you can pot them in soil such as you would use for African violets or a mixture of equal parts of peat moss (or leaf mold), sand and garden loam.
Select squatty pots of clay or plastic. You’ll have less watering to do if you plant in the plastic ones. Place about an inch of drainage in the bottom of the pot. Plant one and one-half-inch tubers in six-inch pots; two-inch tubers in eight-inch pots. For exhibition purposes plant two-inch tubers in ten-inch pots, and others in proportionate sizes.
Plant the tuber so it has a light covering of soil. Place a stake in each pot at planting time. Taller tuberous begonias need light staking to protect them from wind.
To produce sturdy growth and a maximum crop of blooms, feed the plants twice a month with liquid plant food. If the fertilizer you are using doesn’t give specific instructions for use on tuberous begonias, use it only half as strong as that suggested for other pot plants. An overdose of fertilizer may cause bud blast.
For Bigger Begonia Blooms
If you want show-sized blooms, nip out the first buds to appear. As the flowers open you’ll discover that the natural flower arrangement is one large pollen-bearing (male) flower with a single flower on each side of it. Keep these single flowers nipped off and your begonias will grow huge flowers.
If you are entering your begonias in a show get some of the specially designed wire supports made of two pieces of intertwined wire to support heavy flower heads.
Propagation of Tuberous Begonias
You can have more tuberous begonias of a favorite variety by cutting off sprouts and rooting them in any medium, or by dividing old tubers, leaving one sprout or eye to each division. Plant the divisions as you would tubers.
Or you might like to try them from seed. If so, January is the month to plant them. Sprinkle the fine seed atop shallow flats of screened peat moss and sand. Moisten and cover with a glass or ventilated plastic, and place in a cool (65 degrees) dark place.
Germination takes place in eight to 14 days. After the seeds have germinated you can give them a little more light. They are ready for transplanting when they show four good leaves.
You’ll get some late summer bloom from these seedlings.
Dormancy and Tuberous Begonias
Tuberous begonias finish blooming in October and November. When the leaves yellow, withhold water. Store tubers in a cool basement or closet. If you have but a few leave them in the pots. If you have a number, remove them from the soil, dry the tubers in the sun and store them in a box of peat moss or vermiculite.