Tuberous begonias are the most glamorous and colorful of all plants suited for summer culture outdoors in the shade, and they are not difficult to grow. They are available in various forms, colors, and sizes of bloom.
There are single- and double-flowered varieties that may be plain, crested, ruffled, or fringed. They have almost every imaginable color except blue.
Shelter from strong winds is highly desirable, and shade is necessary, especially from 11:00 A.M. to 7:00 P.M. They are admirable when planted in the shade cast by high-headed trees, in window boxes on the shaded side of a house, or in pots displayed on a shaded terrace or patio.
What To Do During Hot Summers
Where summers are hot, it is advantageous to bury the pots to their rims to help keep the roots cool and reduce the need for watering.
Dormant tubers can be planted outdoors 1″ inch deep, about two weeks before tomato-planting time. However, the usual practice is to start them indoors six to eight weeks ahead of outdoor planting time, adding several weeks to their flowering season.
Starting Tubers
To start the tubers, moist peat moss or sand is placed to a depth of about 3″ inches in a pot, pan, or flat, and the surface is leveled without pressing it down. The tubers are gently pressed into the peat, convex side down, barely below the surface.
They are then kept at a temperature near 60° degrees Fahrenheit as possible, with the peat moss moist but not sopping wet. As soon as the shoots are visible, they are transferred to a well-lighted position, and the flats are -given a half-turn every three days so that the young plants do not grow lopsided.
When they’re about 4” inches high, they need a richer rooting medium and should be transferred to 4” inch pots, lifting them carefully.
The soil for potting should be rich and porous and primarily organic in origin. Here are some recipes—choose the one containing ingredients most easily obtained locally:
1. Spent mushroom soil, four parts; coarse sand or 1/4″ inch charcoal (get from the feed store).
2. Loam, four parts; leafmold or peat moss, four pieces; sand, two parts; dried cattle manure, two parts; 1/2 cup bonemeal to each peck of the mixture.
Begonias cannot endure waterlogged soil, so to ensure good drainage put a 1/2″ inch layer of flowerpot chips, or chicken grits, in the bottom of the pot. Set the plant so that the top of the tuber is 1/2″ inch below the pot rim, fill the pot with soil and press it down, lightly, with the fingers.
Keep the plants in a sunny window, shading them from the bright sun with plastic or woven curtains. Do not forget to give them a half-turn every two or three days to ensure their shapeliness. Their next move will be either to larger pots, 6″, 8″ or 10″ inch “azalea pots” (3/4-depth pots), or bulb pans (1/2-depth pots); or to be planted in a bed outdoors.
Before they go to their summer quarters, they should be gradually inured to outdoor life by keeping them in a cold frame, exposing them increasingly to open air.
Prepare the soil for outdoor planting by spreading a 3″ inch layer of peat-moss and rotted manure, or just peat-moss; plus 5-10-5 fertilizer at the rate of 6 ounces to 10 square feet; the whole to be thoroughly mixed with the upper 4″ inches of soil. Set the plants 9″ to 12″ inches apart, with the top of the tuber 1″ inch below the surface.
The soil should be kept moist, whether in pots or planted. It helps them tremendously during hot weather if they are sprayed with water every evening.
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