Begonia
by Tom Rood
NYS Master Gardener Program

Begonias have been around for a long time. There are so many varieties, from 1000 to 2000, that any attempt to cover them all would be difficult if not impossible. They range in size from those grown in tiny tea cups to ones that will cover a barn wall. Some are grown for their colorful foliage, others because of their tendency to cascade from hanging baskets or wall mounted flower boxes. Still others grow upright and make excellent potted house plants or great garden borders. From greenhouse container plants, house potted plants and garden bedding plants, the begonia we know today is a very versatile plant as well as one of the most beloved easy-to-grow plants. The flowering types have a very long bloom season.

Botanically, there are three main begonia groups of interest. The roots of the begonia determine which group they belong. B. rex is the variety grown mostly for its interesting and distinctive foliage colorization, has rhizomatous thickened root stems which can be used for propagation. It is not a long lived indoor plant but easily propagated through leaf cuttings. The tuberous group (b. tuberhybrida) has thick roots and is the most popular begonia. Upright and cascading flowering tuberous begonias belong here. Some of the flowers from upright begonias will reach 6" across and come in just about every color except blue. These roots can also be used for propagation. The wax begonia (B. semperflores) has ordinary fibrous roots that can not be used for propagation. This bushy begonia usually grows only 6 to 12 inches tall and depending upon growing conditions may bloom anytime of the year.

There is a fourth begonia that might be found in some nurseries or greenhouse operations. This is the Rieger begonia which is a patented hybrid from B. socotrana and can not be legally propagated without a license for commercial sale.

All the begonias we grow today are hybrids. In some cases, as in B. rex, the original species begonia has been lost. Lost means it can no longer be found. The name begonia originates from the 17th century and a Frenchman Michel Began, a patron of early botany and once governor of French Canada. For over 100 years, begonia plants have been hybridized to produce hundreds if not thousands of newer varieties. The easiest way to get started with begonia is to purchase one or more plants from local growers or to propagate them from cuttings obtained from friends.

Tuberous begonias (upright and hanging basket types) should be planted in March for summer bloom. Plant in a 4" pot filled with a good peaty soil mix. The concave side of the tuber should be facing upwards with the top just visible. Moisten potting soil thoroughly and allow to drain. When new shoots are 3" to 4" inches tall transplant to a 6" pot if space is a problem or into an 8" pot for summer blooming. Bright light but not direct sunlight will aid growth. They like cool temperatures 60 to 70 degrees F and high humidity which is a problem for most home-grown indoor plants. Begonias do not like hot temperatures. The potting medium should be kept slightly moist. Fertilize every other week with a good liquid fertilizer following label directions.

In summer the tuberous begonia can be grown on the shady patio or filtered light area in the garden. Follow normal gardening watering and fertilizing as with most other garden plants. In fall after bloom is over, with hold all fertilizer and reduce moisture allowing the leaves to wilt. Dig up or remove the plant from the pot and store in dry peat moss. One method of storing tuberous begonia is to place the tubers in a discarded mesh bag (the kind used for onions and oranges), filled with dry peat, from a cellar ceiling where the winter time temperatures hover in the low 50 degree F range.

Tuberous begonias are easy to propagate by stem cuttings. If the tuber sends up multiple stems, some, but not all, may be cut flush with the tuber surface. Dip the cut end in a rooting compound place it in moist sand. Slip the cutting and container holding the rooting medium in a large clear plastic lock top bag to seal in moisture and to keep the cutting from drying out. Place the cutting in bright but not direct sunlight. Best rooting temperature seems to be near 65 degrees F. If started in March, it should be ready to bloom in summer.

Three to four cuttings can be started just about anytime during growing season. Cuttings should be higher up on the plant rather than lower down along the stem. Lower cuttings tend to grow more foliage by not expending energy to produce flowers. Make the cut about 1/4 inch below a leaf. Remove the lower leaves from the cutting. Dip the cut end in a rooting compound and place in moist sand. Follow the lock top bag procedure and
light requirement as above.

Tubers can be divided too. First step is to get the tubers growing in March. When buds (eyes) first start to appear, remove the tuber from the growing medium and divide with a sharp knife leaving at least one eye per cut division. Dust with a general purpose fungicide following the label directions. One source recommends dusting with powdered charcoal. Let these divisions air dry for a few days. Plant in moist sand with the eyes
on top. At one to two inches of growth replant in regular growing soil mix.

Tuberous begonias can also be started from seed. Start seeds in January for summer flowering. When planting the seeds, avoid too much water. Over watering seeds and seedlings invited damping off fungus. A good sterile seed starting mix is important to success. Bottom watering tends to help avoid damping off. Allow the seed flat to drain thoroughly after watering. Sprinkle the tiny seeds over the surface of the soil mix leaving them where they fall. Do not try to cover the seeds. Place the flat into a clear plastic lock top bag to retain moisture. Place the bag where the seeds can receive light for germination but avoid direct sunlight. Best germination temperature is reportedly between 65 and 70 degrees F. Germination should only take about a week.

When the tops of the new seedlings begin pushing up on the top of the bag, open the bag to allow a little air to circulate inside for a day or two. When condensation on the inside surface of the bag is greatly reduced, remove the seedling flat from the bag. One of the things that happens to seedlings grown indoors is that they tend to fall over. A small fan
blowing softly over the foliage will cause strengthening of the plant stems helping them to remain erect. The fan also is a good deterrent to damping off fungus as it removes excess moisture. Weak light conditions cause seedling to grow tall and spindly. Experience will help know when this becomes a problem. After a couple of sets of true leaves are formed the seedling should be transplanted to small seedling pots again using a good starting soil mix. A very dilute liquid fertilizer can be used after the seedlings begin growing. Too much fertilizer may burn the leaves and roots of the plant as well as provide toxic build-up (toxic to the plant) in the soil.

Start seeds for Wax Begonia in January for summer bedding plants and for window boxes. Wax begonias can be dug up in fall and grown over winter indoors. In September, wash off plant to remove any hitch hiking insects, dig whole plant, cut stems back and repot before bringing indoors for winter.

For all your lawn and garden questions call the Master Gardeners at the Cooperative Extension office 315-536-5123 leaving your name, question, phone number and a time we may return your call with the results of our research. If you are interested in becoming a Master Gardener, a new class will be forming in January. Call the Co-op Ext office for details.