Gadenin日本語Get the appWhy the middle goes bare
A petunia flowers at the growing tip. As each stem extends, the flowers move outward with it, the older leaves behind them are shaded by the plant's own growth, and they yellow and drop. By the middle of summer you are left with a ring of flowers around the outside of the basket, a wall of bare brown stems in between, and nothing at all in the center. This is not a disease, a deficiency or a watering fault, and no amount of extra feed reverses it.
It happens sooner in the trailing basket types than the bushy bedding sorts, because a trailing stem can put on three feet (90 cm) of length in a season. It also happens sooner on plants that have been fed heavily with nitrogen, which lengthens the gaps between leaves, and on plants in too little light, which does the same thing.
The only fix is to remove length, which forces the buds that are dormant along the bare stems to break. Those dormant buds are there in the leaf axils the whole time; they stay asleep as long as the growing tip above them is active. Cut the tip off and they wake up within a week.
Cut back by a third when the middle goes bare
Take the whole plant down by a third to a half. That looks brutal on a basket that still carries flowers at the ends, and it is the single thing that most gardeners cannot bring themselves to do, which is why so many baskets are written off in high summer. Leave at least four to six inches (10 to 15 cm) of stem with leaves or visible leaf joints on it, and never cut back into bare woody stem with no joints at all, because there is nothing there to shoot from.
Cut each stem just above a leaf joint. Two shoots usually break from that joint, so a plant cut back sensibly comes back denser than it was. Vary the length you leave from stem to stem rather than shearing the whole thing to one level; a shorn plant regrows as a flat mop, while a plant cut at staggered heights refills with some depth to it.
Water the plant well the day before, and cut in the morning or evening rather than in full afternoon heat. Feed immediately after cutting, because the plant is about to build a lot of new tissue and the compost in a basket has nothing left in it by this point in the season. Expect new shoots within seven to ten days and flowers again in two to three weeks.
- Water and feed the day before A plant cut back while dry sulks for an extra week. Soak the basket thoroughly, and give a full strength liquid feed so the nutrients are in place when the new shoots break.
- Take a third off, cutting above leaf joints Follow each long stem back to where there are still leaves or visible joints and cut just above one. Leave four to six inches (10 to 15 cm) of leafy stem minimum.
- Stagger the cut heights Cut some stems shorter than others rather than shearing everything level. That gives depth to the regrowth instead of a flat top.
- Clear out the debris Pull every dead leaf and spent flower out of the crown while you have access to it. Left there through the following wet week it starts gray mold in the fresh cuts.
- Feed weekly from then on Regrowth is entirely dependent on what you give it. Weekly liquid feed at full strength, higher in potassium than nitrogen, until the flowers come back.
Cutting a third of the stems at a time, if you cannot face it
If the basket is on show and you cannot accept three flowerless weeks, cut a third of the stems hard, leave the rest, and repeat on another third two weeks later, and the last third two weeks after that. The plant is never entirely without flowers and the whole basket is renewed inside six weeks. It is slower and fiddlier than one clean cut, and the result is slightly less even, but it is far better than doing nothing.
The same staggered method is worth using on a mixed container where the petunias are only part of the planting, because a single hard cut leaves an obvious hole next to companions that are at their peak.
| Approach | When to use it | Flowerless period |
|---|---|---|
| One hard cut, a third off everything | Midsummer, plant clearly bare in the middle | Two to three weeks |
| A third of the stems every two weeks | Basket on show, cannot lose the display | None, but renewal takes six weeks |
| Pinching tips only | Early season, plant still young and short | None |
| No cutting at all | Late in the season, cold nights coming | Not worth cutting; the plant will not regrow |
Pinching early is what prevents the problem
A young petunia pinched twice in its first six weeks never gets as leggy as one that was not. When a plant has four or five pairs of leaves, take out the top half inch (12 mm) of the main shoot. Two side shoots break from below the pinch. Pinch each of those once more when they have three or four pairs of leaves, and you have a plant with eight growing points instead of one, all flowering, all short.
The cost is that flowering starts about two weeks later than on an unpinched plant. That is a real cost in a short season and no cost at all over a full summer, because the pinched plant is still full and flowering long after the unpinched one has gone bare in the middle. Pinch at planting out and again three weeks later, and the first hard cut back may not be needed until well into the second half of summer.
Do not pinch after the middle of summer as a way of tidying. At that stage the plant needs length removed, not tips taken out, and pinching the ends off long bare stems simply gives you two bare stems where there was one.
Note the date you cut back and the date the flowers returned. Two seasons of that tells you how long your own regrowth takes, which is what decides whether one hard cut or three staggered ones fits the summer you have.
When cutting back is no longer worth it
Late in the season, once nights are consistently cool and the light is going, a cut back plant regrows slowly and may not flower again before frost. As a working rule, do not make a hard cut within six weeks of your first expected frost. Deadhead, feed and let it run out instead.
A plant that has been cut back twice, is woody at the base, has thin pale regrowth and yellowing throughout despite feeding, has simply had its season. Petunias are grown as annuals in most climates for exactly this reason. Take cuttings from clean healthy shoot tips if you want to carry the plant over, and compost the parent rather than trying to keep it going another month.