Gadenin日本語Get the appWhy this crop is pinched at all
A broad bean plant keeps extending upward and keeps producing soft, sappy growth at the very top for as long as it can. That tip tissue is the only part of the plant that black bean aphid can feed on easily, and it is where a colony always starts. Remove the tip and you remove both the aphid's landing site and the plant's incentive to keep growing taller instead of filling the pods it already has.
This is the whole of broad bean pruning. There is no formative pruning, no summer thinning of shoots, and no cutting back to a bud. One cut, at one moment, on each stem. Everything else you might read about pinching or stopping this crop reduces to that.
Pinching also lowers the plant's center of gravity slightly and stops it running up into wind, which reduces how often a heavily podded row leans over. It is not a substitute for string supports, but it helps.
The right moment: once the lowest pods have set
Pinch when the bottom three or four flower trusses have set small pods, roughly an inch (2.5 cm) long, and the plant is still flowering higher up. That timing means the plant has already committed to a full crop and the flowers you remove would not have had time to fill anyway. Take the tip earlier and you cut real yield; leave it until aphids are established and you are removing an infestation rather than preventing one.
In practice this lands around the time the plant is two and a half to three and a half feet (75 to 110 cm) tall, but height is a poor guide because autumn-sown plants and spring-sown plants reach that point at very different sizes. Look at the pods, not the ruler.
Take about four to six inches (10 to 15 cm) off: the soft tip and the top pair or two of small leaves, snapped off between finger and thumb. If it snaps cleanly it was soft enough to be worth removing. If you have to cut it with a knife you have gone too far down into woody stem, and you are removing pod-bearing tissue for no reason.
| Stage | What you see | Pinch or wait |
|---|---|---|
| First flowers open, no pods yet | White and black flowers at the lower nodes | Wait. Pinching now cuts your crop |
| Lowest three or four trusses hold pods an inch (2.5 cm) long | Small flat pods pointing upward, flowering continues above | Pinch now. This is the moment |
| Aphids already dense on the tip | Black clusters on the growing point and top leaves | Pinch immediately and take the removed tips off the plot |
| Pods filling, top flowers dropping without setting | Fat pods below, empty flower stalks above | Pinch. Those top flowers were never going to fill |
| Autumn-sown plants with several stems | Three or four stems from one crown at different heights | Pinch each stem separately as it reaches the pod-set stage |
How to do it, stem by stem
Work along the double row from one end so you do not miss plants, and treat each stem as its own job. Autumn-sown plants commonly carry three or four stems from the crown, and they will not all reach pod set on the same day, so expect to go back over the row two or three times across a week or ten days.
- Check the lowest pods on that stem Find the bottom flower truss and confirm it holds a small pod rather than a spent flower. If the bottom trusses are still flowers only, leave that stem and come back in a few days.
- Snap out the top four to six inches (10 to 15 cm) Bend the soft tip sideways between finger and thumb until it breaks. Take the growing point and the top one or two pairs of small leaves. Do not cut into firm stem.
- Look at the tip you removed Turn it over. Any aphids on it tell you the colony has already started, which means you should check every remaining plant in the row the same day rather than waiting.
- Carry the tips off the plot Do not drop pinched tips on the soil under the row. Aphids walk back up. Bag them or bury them in the middle of a hot compost pile.
- Eat the clean tips Aphid-free tips are a good vegetable, cooked briefly like spinach. This is the one part of pruning this crop that pays you back on the same day.
What not to cut
Do not remove side stems from the base. Every stem a broad bean throws from its crown is a pod-bearing stem, and thinning them is a habit carried over from tomatoes that does no good here. A well-rooted overwintered plant supports four stems comfortably.
Do not strip lower leaves to improve airflow. Broad bean lower leaves feed the lowest pods, which are the ones that fill first and largest. If chocolate spot is spreading up the plant, wider spacing next season is the answer, not defoliation this season.
Do not cut the whole plant down after the first flush hoping for a second. Broad beans do not regrow usefully from a cut stem. When the pods are picked, the plant is finished. Cut it off at ground level and leave the roots in place, because the nitrogen-fixing nodules on them are worth more to the next crop than the plant is to you.
What to record
Note the date you pinched each row and whether aphids were already present on the tips you took off. Over a couple of seasons that pairing tells you exactly how early the aphids arrive where you garden, and whether your autumn-sown row is genuinely beating them or only just.
It is also worth writing down which sowing needed pinching first. If the spring row consistently gets hit before it reaches pod set, that is a strong argument for shifting more of the crop to autumn sowing rather than for spraying anything.