Growing Tuberous Begonias From Seed to Flower

Tuberous begonias have fittingly been called the mocking birds of the floral kingdom. It is an apt comparison, for like its counterpart in the bird world, the tuberous begonia mocks other flowers in color and form.

It will produce blossoms resembling marigolds, hollyhocks, camellias, carnations or roses. As hanging baskets the plant is queen of the field.

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A subtle blending of color makes the flowers seem out-of-this-world. All colors and variations from cold glacial white to glowing black red are to be found.

They include delicate pinks, some with an undertone of warm ivory, rose, flaming orange. scarlets that appear to be on fire, and a dark red appropriately culled Satan. There is no blue begonia and due to the possible color combination’s, there can never be one.

The tuberous begonia originated from Begonia boliviensis, grandmother’s window-garden begonia, which had semi-pendent growth and thin long-petaled single orange flowers.

The first known cross was made in 1870 in England, with Begonia boliviensis and a species, which was never named, as parents.

This kindled enthusiasm and other species were sent to England for use as foundation stock. Six species with typical single flowers entered into early hybridization:

  • Begonia Boliviensis
  • Begonia pearcei
  • Begonia veitchi
  • Begonia rosaeflora
  • Begonia davisi
  • Begonia clarkei

The early hybridizing was done by English growers, (Rieger begonias use Tuberous as a parent) but in the past 75 years growers in California have made tremendous advances with many new varieties.

It is amazing to see seedling plants from a December sowing burst into a blaze of color by the middle of July and continue in blossom until stopped by frosts.

Still more amazing is the fact that from each seedling we may then harvest a tuber from 1-1/2 to more than 2 inches in diameter, which will annually repeat the cycle of growth and bloom

Germination of the brown, dustlike seed is not difficult if it is given proper attention. Of first importance is the choice of seeding media, preferably peat moss or decomposed oak leafmold, and secondly its preparation.

Germinating Tuberous Begonias

The initial step is sterilization – steam always works well.

A total of three screenings is made, resulting in one of the finest possible sowing beds for fine seeds such as those of the gloxinia, Streptocarpus, ramonda, azaleas, rhododendrons and shortia.

To screen correctly, do not force the material through the screen, but rather silt only that which will drop through with four or five rockings of the screen.

First, sift the sterilized soil (peat moss works well) through a screen of 1/2-inch mesh, placing the coarse leaves and twigs to one side, to be used in the bottom of the flat for drainage.

A 3/16th-inch mesh screen is used next. The screened portion of soil from this operation is retained for the final screening, and the coarser remainder is saved to be used as the center rooting layer.

This should be neither too coarse nor fine but of an open spongy texture in which the threadlike roots may form and readily draw sustenance.

The screened material from the second sifting is passed through a 1/16th-inch screen. The soil which does not pass through the screen is used as the topping or surface for sowing.

Rock the screen only enough to eliminate the fine dust which is discarded.

A nursery flat or shallow box is best for sowing, although clay pots will also serve well. The depth of soil in the completed flat or box should not exceed 1 inch.

A thin layer of the coarse screened material left from the first sifting is placed over the bottom of the flat. Then the middle rooting layer left from the second sifting is added and lightly leveled with a float or piece of board.

Over this the topping, left from the third sifting, is evenly scattered to a depth of 1/8th inch. It is on this surface that the seed is then broadcast. Do not firm the surface.

The use of this coarse surface reduces damping off to a negligible percentage. Should a spot of disease appear in the coarse topping, it is possible to encircle it with a knife or pencil point and halt it by allowing the spot of infection to become bone dry.

Sowing Tuberous Begonia Seed

When the sowing surface has been leveled, moisten it slightly by spraying with sterilized water, which must be used at all times when watering is necessary.

The actual sowing of the seed should be a deliberate and unhurried job, so that seed may be distributed evenly over the surface. Sowing too thickly will result in crowded, weakened seedlings.

Several methods of sowing may be used: the seed may be mixed with twice its bulk of fine sand and scattered over the sowing surface with a salt shaker.

Or crease a heavy card to make a channel and fill it with seed. By tapping the card lightly with a lead pencil, the seed may be spread over the flat or planted in rows an inch apart.

One nursery sows seed by placing it in the hand of the right hand, rotating the hand over the flat and at the same time tapping the wrist with the left hand. This last method requires some practice to coordinate the movement of both hands.

The seed should not be covered or firmed into the soil after sowing. Carefully spray the surface with an atomizer to moisten the top 1/2 inch of soil. Then place a pane of glass over the flat and a sheet of newspaper over the glass to exclude all light.

Check the flat every two or three days to see if additional watering is necessary and to dry any water drops which cling to the glass.

Next in importance to correct soil moisture is the proper temperature. A good, even germination is induced by a constant bottom and top heat of 74 degrees.

At this temperature, there should be a general cracking of the seed coat on the seventh day, and on the eighth or ninth day the seed leaves will appear.

The newspaper should be removed as soon as the seed coat cracks. The flat should then be exposed to light but not direct sunlight.

At this time the glass is raised slightly with a matchstick to admit air, and is removed completely when the tiny plants begin to form roots, usually three or four days later.

The surface must never be allowed to dry for a moment, and all watering should be done early enough for the foliage to dry before nightfall.

When the first true leaf has attained a diameter of 1/8 inch it will be beneficial to feed the seedlings weekly with diluted fish emulsion at the rate of 1/2 tablespoonful per gallon of water. This is a safe fertilizer and will promote strong growth and good color.

Transplanting Tuberous Begonia Seedlings

As a general rule, the growing begonias are transplanted when the largest seedling leaf is about the size of a dime, within six or eight weeks.

Again the preferred medium is fairly coarse leafmold which has been passed through a 1/2-inch mesh screen. After transplanting, flats should be carefully watered to prevent the soil from becoming soggy.

At this stage plants may be fed once every two weeks with fish emulsion at the rate of 1 tablespoonful to a gallon of water. A second transplanting when the plants begin to crowd will repay the grower with a larger root system and heavier and stronger plants.

Outside, the plants like a semishady location under light-foliaged trees on the north side of the house, or the protection of a lath house.

The plant reaches its maximum growth and flower production in a cool, moisture-laden atmosphere in a situation with sufficient shade to cut the direct burning’ rays of the sun.

Too much shade will result in rank vegetative growth; too much sun will dwarf and injure the plant.

Providing for Drainage

Perfect drainage is important. The planting area should be well prepared in advance, replacing unfavorable soil to a depth of 12 inches with a fertile fibrous loam to which enough sand has been added to permit thorough drainage. Well-rotted cow manure may also be mixed with the soil.

Do not plant too deeply. The soil should never be pulled around the plant stalk, as this will induce rot. A tablespoonful of fishmeal mixed in the planting hole under the plant will give luxuriant growth. For a massed effect the plants should be spaced 9 to 12 inches apart.

Each plant should be provided with a light bamboo stake at planting time, since heavy blossoms should be supported.

Tuberous begonias need a well-drained soil. They will not tolerate wet, ill-drained soil around the tuber. Overwatering is the commonest cause of bud drop; it is better to water moderately.

They are shallow-rooted plants and should be -treated accordingly. Do not cultivate around them with sharp tools; use your fingers to weed or to loosen soil.

Fading blossoms must be removed before they fall within the plant or around its base. Decaying matter coming in contact with any part of the live plant tissue will quickly cause rot which will destroy the plant.

When a spot of decay is noted it should be cut back to healthy tissue and the wound painted with a thick paste of a fungicide like captan and water.

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