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Starting Tuberous Begonias Off Right

By Contributor ; Updated September 21, 2017

by Susan Ward

© Susan Ward; All Rights Reserved.

If you have shady garden areas or are looking for a brilliant accent for your patio or balcony, you'll want to start some tuberous Begonias indoors in March or April. Tuberous Begonias provide a spectacular display from June through October and are available in shades of white, pink, red, yellow, orange, and salmon as well as bi-colors and picotee, flowers with darker edging around all the petals.

Begonia Types

The most spectacular of all are the Begonia tuberhybridia, which grow about 10 to 12 inches tall and have rose- or camellia shaped double blooms up to six inches wide. The Benary Company in Germany has developed an F1 hybrid called 'Non-Stop', named because they bloom earlier and become dormant later in the fall than regular tuberous Begonias. In fact, if you move them indoors or into a greenhouse where they can receive light during part of the night, they actually can bloom through the winter 'non-stop'! They're also more heat tolerant and supposedly easier to grow. The drawback is that their flowers are not as large or fancy as those of the giant hybrid varieties, and so far, there are no 'Non-Stops' with the dark picotee edges that I find so appealing. (Buf if you're a picotee fan too and want to try 'Non-Stop' begonias, look for 'Pin-Up', which has large, single white flowers with rose edging.)

Two other forms of tuberous begonias are Begonia multiflora, which has smaller but more plentiful flowers and grows about 8-10 inches tall, and Begonia pendula, which as you would guess, is a hanging type, ideal for baskets. You can buy Begonias as bedding plants, of course, but starting them from tubers is much less expensive.

Selecting Tubers

Tubers for all three of these types of Begonias are available now at garden centers and nurseries; they look like small brown lumps with a depression on one side. Choose only firm tubers and look for those with tiny sprouts showing on their upper, concave surfaces. Examine the tubers carefully for soft spots or rot before purchasing.

Planting Begonia Tubers

Prepare seed trays or small clean pots about 2 to 3 inches deep with adequate drainage holes with a mixture of good organic compost. If you're using commercial potting mix, mix it with equal parts of peat moss and sand or perlite.

Place each tuber hollow side up just below the soil level. The tuber should have no more than half an inch of light soil covering it. (They rot easily if planted too deep.) Water the tubers once really well, to wake them up, and place them in a warm, bright spot where the temperature will never fall below 16-17° C (60° F). Cover the freshly-planted tubers with paper or polythene to promote growth, but remove the covering as soon as growth appears. Don't water again until you see some growth or the soil is quite dry; the begonias don't have any roots yet and you don't want to drown them. Some begonias will sprout right away others will take weeks; generally, expect to see growth shoots in five to six weeks.

Once They're Growing

Once the shoots are showing, water regularly, never allowing the soil to dry out. Give maximum light, but shade from direct sun. Applying liquid plant food will improve your Begonias' growth; feed them with half strength balanced fertilizer the first time when their leaves and stems are about 3 inches tall, wait two weeks, and then start a regular feeding schedule. When the shoots are 6 inches tall, the Begonias are ready to be transplanted to the garden or outdoor containers. Don't put them outdoors, though, until all danger of frost has passed, and remember to harden them off properly.

General Care

Tuberous Begonias thrive in partial to full shade and need well-drained soil. They need to be kept away from hot sun and drying winds. As they dislike dry conditions, they'll need to be watered generously, especially during hot weather. Keep their soil moist but not soggy; the tubers will rot if they get too much water. Always water the soil around the plants rather than the plants themselves, if possible, to avoid mildew, and at the first sign of a white patch on any of your begonias' leaves, apply a fungicide right away. Feed Begonias with a well-balanced plant food every 2 to 3 weeks.

For appearance's sake, pinch off extra or too-long stems as the plants are developing, keeping the three strongest stems and pinching off the others. Large flowered Begonias look best with fewer, larger flowers, and you don't want your begonias to get leggy. Pinch off the early developing flowers, too, until the plants are 10 inches tall.

If you're growing pendant types and want to make sure they have lots of branches to cascade down from their pots, pinch out the primary growing tip when the plant is about 2 inches tall.

You'll also want to deadhead all your Begonias regularly; removing wilted leaves and flowers encourages them to produce more blooms. The large-flowered types of Begonias should be staked.

Storing Begonias

Once the show is over in the fall, you'll be able to dig and store your tubers until spring rolls round again. Because Begonias are prone to rot if left in the ground until their tops fall off, I recommend bringing them indoors before frost. If you place them in a well- ventilated room and start withholding water, the foliage will die back and you'll be able to remove the stems and leaves without damaging the tubers. Clean them off, dust with soil dust, and cover the tubers with dry sand, peat moss or vermiculite; store them in a cool, well-ventilated, frost-free area such as a garage over winter. (55° F is ideal.)

Properly stored, tuberous Begonias will give you years of vibrant, eye-popping blooms to brighten up your shady garden areas. So get your tubers started now for a show- stopping summer!

About the Author Susan Ward is an ex-English Teacher who now earns her living by writing. She is author of the column "Gardening in B.C." at Suite 101.


About the Author

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