Gadenin日本語Get the appDisbudding: take the small single flowers off
Tuberous begonias carry their flowers in threes. In the middle is the large double bloom, which is the male flower and the reason the plant is grown. On either side of it, on short stalks from the same joint, are two much smaller single flowers with four petals and an obvious three winged triangular swelling behind them. Those are the female flowers, and that winged swelling is the developing seed pod.
Left in place, those two female flowers set seed, and seed production draws sugars away from the central bloom. The effect is not subtle. On a plant disbudded properly the central flowers come noticeably wider, thicker in the petal and longer lasting, and the plant keeps producing new trusses for weeks longer. On a plant left alone the flowers are smaller, the display finishes earlier, and the winged pods swell up and then rot in the middle of the plant in wet weather.
Remove them as early as you can see them, when they are still the size of a pea and the winged pod behind is barely formed. Pinch each side bud off between finger and thumb, taking the whole small stalk with it, or snip it with the point of a pair of scissors. Doing it early costs the plant nothing; doing it after the female flowers have opened wastes everything the plant has already invested in them, though it is still better than leaving them. The one reason to leave them is if you want seed, and begonia seed does not come true from garden plants, so almost nobody does.
- Find the truss Follow a flower stalk to where it divides. You will see one fat central bud and two smaller ones flanking it, all from the same point.
- Identify the female buds by the winged swelling The two side buds have a three sided winged green pod immediately behind the petals. The central male bud has no such swelling behind it.
- Pinch both side buds off while tiny Take them at pea size, removing the short stalk as well. Both sides, every truss, right through the flowering season.
- Support the remaining bloom A properly disbudded double flower is heavy enough to bend or snap the brittle stem. Put a slim cane in behind the main stem before the buds open, not after.
- Deadhead the central flower when it goes over Snap the whole spent flower stalk out at its base rather than pulling the petals off. A stalk left behind rots and becomes the start of gray mold in the crown.
Pinching young plants to get a branched shape
A young begonia of any type left to itself runs up on one stem and flowers thinly at the top. Pinching out the growing tip when the plant has three or four pairs of leaves makes two side shoots break from the joints below, and pinching each of those once more gives a plant with four or more flowering points instead of one. On bedding types this is the difference between a gappy planting and a solid one; on tuberous types it is worth doing once but not twice, because every pinch delays the first flowers by about two weeks and the season is not long.
Trailing tuberous types grown in baskets are the exception. Pinch these twice, early, and accept the delay, because a basket with four or five trailing stems from each plant covers the sides and a basket with one does not. Stop pinching once the stems have started to hang over the rim.
Cane stemmed begonias respond differently again. A pinch on the tip of a cane makes it branch, but the more useful cut on a mature plant is to take one of the oldest tallest canes right down to two or three joints above the compost. That forces a completely new cane from the base, which is the only way to keep an old plant furnished at the bottom rather than a set of bare poles with leaves at the ceiling. Take one cane a year rather than all of them at once.
| Type | Pinching | Hard cutting back |
|---|---|---|
| Fibrous bedding | Pinch once at four pairs of leaves | Shear by a third in midsummer if it goes leggy |
| Upright tuberous | One pinch only; more delays flowering too long | None during the season; the top dies back in autumn |
| Trailing tuberous in a basket | Pinch twice while the stems are still short | None; cut the whole top off after it yellows |
| Cane stemmed | Pinch tips to branch | Take one oldest cane to two joints above the compost each late winter |
| Rhizomatous foliage | Do not pinch; there are no stems to pinch | Remove old leaves at the rhizome and shorten the rhizome when it overhangs the pot |
Cutting back through the season and at the end of it
Fibrous bedding begonias in a hot summer eventually stretch, go bare at the base and flower only at the tips. Shear the whole planting back by a third, feed it, and it refills and flowers again within three weeks. Do that once at midsummer rather than nibbling at it repeatedly. Do not cut back within six weeks of your first expected frost, because the regrowth will not have time to flower.
The end of season cut on a tuberous begonia is a different job and the timing is the whole of it. As the days shorten the plant stops flowering and the leaves start to yellow. Do not cut the top off at that point. Every day the yellowing leaves stay attached, they are moving stored sugars down into the tuber, and a tuber cut off green is a small weak tuber next spring. Wait until the stems have yellowed thoroughly and separate from the tuber with a light tug, or cut them off an inch (2.5 cm) above the tuber once they are clearly dead.
On rhizomatous foliage begonias, pruning means removing whole leaves rather than shortening stems. Cut any leaf that is more than half damaged right back to the rhizome with the whole stalk, because a stub left behind rots. When the rhizome grows out over the pot rim and starts to hang, cut the leading section off with a clean knife and lay it flat on fresh compost in another pot, where it will root and grow on as a new plant.
Record the date you disbudded each plant and the width of the largest flower it produced. One season of that comparison against an undisbudded plant settles the question permanently, and the notes also tell you how early in the season the female buds start appearing on your plants.
Tools, timing and the mistakes that cost flowers
Begonia stems are brittle, hollow and full of water. They do not tear cleanly. Use a sharp blade or fine scissors rather than pulling, and support the stem below the cut with your other hand, because the weight of the top will snap a cane at a joint if you let it swing. Wipe the blade between plants if any of them have shown rot, and cut in the morning so the wounds have a dry day to seal over.
The three mistakes that cost the most are leaving the female buds on, cutting the top off a tuberous plant while it is still green, and shearing a bedding planting so late in the season that it cannot regrow. All three are timing errors rather than technique errors. A fourth, on indoor plants, is tidying away every flower stalk from a foliage begonia the moment it appears; those flowers are thin but they last for weeks in winter, and there is no cost to leaving them on.
Cut material has a use. Every piece taken from a healthy plant while pinching or cutting back is a potential cutting, and begonias root more easily than almost anything else in the garden. A shoot tip four inches (10 cm) long, stripped of its lower leaves, roots in damp gritty potting mix in two to three weeks.