For large, brilliant blooms in open shade or filtered sunlight, tuberous begonias, in their varied forms and colors, can be the answer to your need. Today these gorgeous flowering bulbs are enjoying tremendous popularity, and some amateur gardeners collect them, as they do geraniums, fuchsias, and dahlias, or African violets indoors. Hybrid varieties, far removed from the original species, are truly exotic beauties which are easy and rewarding to grow. They solve the problem of what to consider for part shade, particularly where vivid colors are needed to enliven terraces or porches.
Tuberous begonias are classified according to shape of bloom-camellia-flowered, including the picotee or double marginata; carnation-flowered; single-frilled or crispa, including Begonia crispa marginata; hanging basket; crested; rosebud; B. multiflora; daffodil-flowered; and hollyhock-flowered. The camellia-flowered begonias are very popular. Older varieties, with their smooth margins, did not resemble camellias as much as the newer hybrids, with their ruffled, wavy-edged petals. In the picotee or double mar-ginata class, the edges are of contrasting color and the broad border is usually irregular. They make lovely pot plants.
The carnation-flowered begonias produce smaller, generally heavier blooms in an extensive color range. The lovely single-frilled or crispa begonias have ruffled petals. In one form, Begonia crispa marginata, the edges offer color contrast. Fascination is a delightful variety in this group.
For Hanging Baskets, Planters, and Window Boxes
Hanging-basket tuberous begonias, the cascading types, B. pendula flora-plena, bear single or double blooms on arching stems. As a rule, these smaller-flowering types are more floriferous than the large ones. There is also a strain that produces miniature camellia-like flowers. Crested begonias, B. cristata, have slightly frilled single flowers. These are carried above the foliage. One of the loveliest is Autumn Glow, with apricot flowers crested with dark copper, handsome as an accent plant in a container.
The interesting rosebud types, in shades of rose and pink, are favorites with many gardeners, though the flowers tend to develop poor centers when they mature. Plants have a free-flowering habit. Begonia multiflora is the small-flowered type sometimes listed as nana. Well known and still one of the best is the yellow Madame Helene Harms. On plants to six inches tall, multiflora begonias support flowers high above the foliage. Their compact habit and free-flowering nature make them good for large planters. Excellent, too, for window boxes, they withstand more heat and direct sunshine than the others, especially along coastal areas where fogs prevail.
Daffodil-flowered begonias, represented by a few varieties, are grown chiefly as oddities, especially by collectors. They are interesting specimen plants to include in a group. The hollyhock-flowered begonia, B. martiana, is another novelty, with flowers close to the stem. In sun, plants attain two feet, but under lath or in partial shade, they may grow to four feet. The two-inch single blossoms are light pink, darker in sun. This begonia can be grown for background or accent among a group of potted plants or in a wide planter.
A Hardy Begonia
Another tuberous begonia is the so-called hardy type, B. evansiana, which survives winters on Long Island and is hardy from Philadelphia southward. Two-foot plants have handsome pointed leaves, a branching habit, and an abundance of single, light pink flowers. Stems are a contrasting rosy-red, and there is a white form. Several pots of the hardy begonia at the doorway or in a sheltered corner can be a choice item in the container garden.
Maine Success Story
Certainly, tuberous begonias are well adapted to container culture. One enthusiast, Malcolm Cox of Round Pond, Maine, who has been growing prize-winning plants for over thirty years, plants his more than 200 tubers in individual pots and window boxes. He finds that potted plants, arranged in tiers in front of his white colonial house, can be seen better when raised, since the heavy blooms are inclined to face downward. Furthermore, when grown in the ground, they tend to become spattered by rain or by the garden hose. Mr. Cox prepares a special soil for his begonias-two parts light garden soil, one part old cow manure, one part peatmoss, plus a five-inch pot of bonemeal to a wheelbarrow of mixture. In containers, his begonias are protected by high branching trees that cast filtered shade.
Start Them Indoors
Because of the short growing season in the North, tuberous begonias need an early indoor start to insure bloom by midsummer. Even where the growing period is longer, it is best to start tubers in pots or trays some time between February and April. Tubers can be planted in flats or bulb pans (low pots) in a mixture of equal parts clean sand and peatmoss. Set them with the hollow side up, for this is the top. Barely cover the tubers with the soil mixture and arrange them just an inch or two apart, since they will remain in these flats but a short time. Water sparingly, but do not allow to dry out. A temperature of 70 to 75 degrees F. is fine; if it is cooler, growth will be delayed considerably and you will lose time. Until sprouts appear, light is not necessary, but after that, give full light to insure compact growth. East or west windows are good, but a small greenhouse is even better.
Room for Growth
After the sprouts are an inch or two high, transplant tubers to roomier quarters. They may be well spaced in large flats, but individual four-inch pots are better because roots will not be disturbed when plants are shifted later. You may even take a short cut now and move them to the final containers. The size of the permanent containers will depend on the size of the tubers. If they are two inches in diameter, they will need six-inch pots. Give three-inch bulbs eight-inch pots, a size well suited to large plants. Because glazed pots and wooden containers stay moist longer and do not accumulate mosses and fungi, they are ideal. In window boxes, space plants five to six inches apart, keeping taller kinds in the back and pendulous or multiflora (nana) varieties along the front. To grow well, sprouted tubers need a special potting mixture-equal parts good garden soil, leafmold or peatmoss, old manure (or a small amount of dehydrated), plus sand for drainage. If the plants are in small pots, use this mixture when transferring them to larger pots. When frost danger is over, plants can go outdoors, but shade them for the first week.
Need for Sun and Food
Finally, wherever you place containers, be certain plants receive filtered or light sunshine for about three hours a day, preferably early or late in the day, when rays are not so hot. Many gardeners misinterpret shade to mean the dense shade of low-branching trees. Here, most plants do very poorly. Open shade on the north sides of houses, and filtered and checkered shade through a lacy network of high branching trees offers an ideal environment for these plants. In cooler climates, they can tolerate more direct sunlight. Tuberous begonias are heavy feeders. Even when you prepare the soil richly, plants will need more sustenance through the growing period. Apply liquid fertilizer, according to directions, while plants are growing actively or topdress wth dry manure about every three weeks. But also keep in mind that too much fertilizer can burn foliage and cause bud drop. To send strength into root and leaf development, cut off the first bud while it is rather small (but not if you are anxious for early flowers). After blooming starts, nip off the two small female flowers on each side of the large, showy male blossoms. This will increase its size.
Keep Moist but Not Wet
Always keep plants moist, but not wet. Usually, watering once a day is sufficient, but this will depend on the type and size of containers, their placement, and the weather. Move plants around until you find places where they grow best. Also, turn them to prevent one-sided development. As plants get tall, they will need support for the heavy blooms. When inserting stakes, be careful not to strike the tubers, and use raffia or soft twine to secure the tender stems. In some cases, extra large blooms will need individual tying, and there are specially cushioned supports of English make for this purpose. From time to time, syringe foliage, preferably in late afternoon or early evening so it will dry before dark. Avoid sprinkling, however, in moist, foggy climates where mildew can be a problem.
Mealy bugs, white flies, leaf hoppers, and aphids can all be checked with lindane or malathion. For thrips, apply DDT or lindane. Use a poison bait with metaldehyde base for snails or slugs and Bordeaux mixture for bacterial leaf spot. In mildew areas, apply captan or the newer karathane as a precaution. These problems, however, are rather uncommon, and very likely you will not be bothered by any of them.
To Store Tubers in Winter
Tubers can be held over from year to year if stored properly during the winter. In fall in cold areas, frosts will blacken the foliage, but in warmer regions the need for rest will be indicated by yellowing without actual frost. Usually this occurs in October, when it is advisable to withhold water. After frost kills tops or they turn yellow, lift plants carefully with a spading fork so as not to injure them. Then, with the tops attached, spread the tubers in the sun for a few hours to dry. After the drying period, cut off tops; but if a portion of stem remains, do not break off. Allow it to dry before removing it later.
Finally, shake off the soil, arrange tubers in trays or shallow boxes, and cover with dry peatmoss or clean, dry sand. The ideal storage temperatures is 45 to 50 degrees F. Some gardeners winter the clean tubers in paper bags, keeping the same colors together, and results are just as good. You can also leave tubers in pots. In this case, simply turn containers on sides and store in cellar, basement, shed or other frostproof spot where temperatures remain 40 to 60 degrees F. If kept too warm, bulbs tend to shrivel and their future as handsome pot plants for locations in filtered sunlight is seriously jeopardized.