Gadenin日本語Get the appWhere the fruit actually comes from
Left alone, a bitter melon plant sends one main stem straight up to the top of whatever you have given it, carrying mostly male flowers on the way. Female flowers, the ones with a tiny warty fruit already formed behind the petals, appear overwhelmingly on the side shoots that break from the leaf joints of that main stem, and on the shoots that break from those in turn.
That is the whole logic of pruning this crop. A plant that has not been pinched spends its first six weeks making a single long stem and a lot of male flowers, and only starts fruiting properly when it runs out of room at the top. A plant that is pinched early is forced to make laterals from the base upwards, and each of those laterals starts setting fruit within a few weeks.
Male flowers open several days before the first females and drop off after a day. Gardeners often report their plant flowering heavily but setting nothing. That is normal at the start and is not a pollination problem.
Pinch the leader at five or six leaves
Take the growing tip out of the main stem once the plant has five or six true leaves, using finger and thumb or clean snips. Within a week or so you will see shoots pushing from the leaf joints below the cut. Keep three or four of the strongest, spread out along the support, and rub out the rest while they are still small.
Those retained laterals become the fruiting arms. Let them run, tying them in loosely as they extend, and they will each throw sub laterals of their own. Female flowers cluster on those sub laterals, so it is worth pinching each main lateral once it has made ten or twelve leaves, which pushes the plant into making them.
- First pinch, at five or six leaves Take out the growing point of the main stem. Do this on a dry morning so the wound seals before evening. The plant checks for about five days and then breaks from the joints below.
- Select three or four laterals Keep the strongest shoots and space them across the support. Rub the surplus out at an inch (2.5 cm) long, before they cost the plant anything.
- Second pinch, on each lateral Once a lateral has ten to twelve leaves, pinch its tip. Sub laterals follow within ten days and those carry the bulk of the female flowers.
- Stop the laterals at the top of the frame When an arm reaches the top of the netting, take its tip out rather than letting it flop back over the outside. A curtain of vine hanging down the far side shades the leaves underneath and is where mildew starts.
What to remove during the season
Beyond the structural pinching, most of the ongoing work is removing things that are in the way rather than shortening healthy growth. Bitter melon has thin leaves and gets shaded out by itself faster than most cucurbits, and a plant that has become a solid mat of foliage stops setting fruit in the middle even while the outside is flowering.
| What to remove | When | Why |
|---|---|---|
| Side shoots from the lowest two leaf joints | As soon as they appear | They sit in still air near the soil and rarely carry good fruit |
| Yellowing lower leaves | Any time from mid season | They contribute nothing and hold moisture against the stem |
| Sub laterals crowding the middle of the frame | Whenever the middle looks solid | Air has to move through the plant or mildew takes the lower leaves |
| Tendrils gripping fruit stalks | On sight | A tendril wrapped around a young fruit constricts it and deforms the shape |
| Misshapen or stalled fruit | As soon as you see it | A fruit that stops growing at an inch (2.5 cm) is not going to recover and is drawing on the plant |
Do not strip leaves wholesale in an effort to let light in. Bitter melon fruit exposed to full sun on a hot afternoon scalds, going pale and papery on the upper surface. Thin for airflow, keep enough leaf to shade the fruit.
Late season cutting back
By late summer the oldest laterals will have fruited themselves out and turned thin and pale at the tips. Cutting those arms back hard, to two or three leaves from where they joined the main stem, prompts fresh shoots that will flower again if you still have six or eight weeks of warm weather ahead. It is the difference between finishing in late summer and picking into mid autumn.
Combine that cut back with a feed, because you are asking the plant to build new growth at the point when its roots are most tired. Water it in properly the same day and expect new shoots within a fortnight.
Keeping notes on the pinching
Record the date of the first pinch and the date you saw the first female flower open. The interval between them is the number that tells you whether you pinched early enough, and it is remarkably consistent from year to year on the same site. If it is longer than about four weeks, pinch a leaf or two earlier next season.
Also note how many laterals you kept per plant and how crowded the frame looked by mid summer. Three laterals on a narrow frame and five on a wide one is roughly right, but the honest measure is whether you could still see daylight through the middle of the plant in high summer, and that is worth writing down while you can see it.