Gadenin日本語Get the appWhy the seed sits there and does nothing
Bitter melon seed is flat, ridged and covered in a coat thick enough that it behaves like a shell rather than a skin. Sown dry into cool ground, a good proportion of a packet simply refuses to take up water, and gardeners who have grown every other cucurbit without trouble assume the seed was old. It usually was not. The seed was intact and waterproof.
Two things fix this: physically breaking the coat, and giving the seed the temperature it actually wants. Bitter melon germinates best between 77F and 86F (25C and 30C). Below 68F (20C) germination becomes slow and patchy, and below 59F (15C) it more or less stops. That is warmer than cucumbers or courgettes need, which is why bitter melon is the last thing in the seed box to be started.
Seed saved from your own fruit works well and stays viable for four or five years, but it must have come from a fruit left to ripen orange on the vine. Seed taken from a fruit picked green is immature and will not come up.
Nick the coat, then soak
The reliable preparation is to open the coat mechanically and then let the seed drink. Done properly, this takes germination from something like half a packet over three weeks to almost all of it in five or six days. Do it the evening before you intend to sow.
- Find the pointed end Each seed has a blunt end and a slightly pointed end where the root will emerge. That pointed end is where you want to break the coat, because that is where the root has to push through.
- Nick or file the shell Clip a small piece off the pointed end with nail clippers, or rub that end on a nail file until the pale inner layer just shows. Stop the moment the color changes. Cutting into the white kernel behind the coat kills the seed.
- Soak in warm water overnight Put the nicked seed in water at about 86F (30C) and leave it eight to twelve hours somewhere warm. Do not go beyond twenty four hours, because the seed starts to ferment and rot. Good seed will visibly swell and feel plump.
- Sow immediately Sow the swollen seed the same day. A soaked seed that is allowed to dry out again is worse off than one that was never soaked, so do not prepare more than you will sow.
Sowing in pots and sowing direct
Most gardeners start bitter melon in pots because it lets you supply the warmth. Sow two seeds to a three inch (8 cm) pot, half an inch (1 cm) deep, laid flat rather than stood on end, and keep the pots at 77F to 86F (25C to 30C) with a propagator, a heat mat or simply the warmest windowsill in the house. Expect the first shoots in five to seven days and pull the weaker seedling once both have their seed leaves open.
Sowing direct works where summers are long and hot. Wait until the soil at planting depth is holding above 68F (20C) and the last frost is well past, then sow three seeds per station, an inch (2.5 cm) deep, and thin to the strongest. Direct sown plants catch up with pot raised ones quickly because bitter melon hates root disturbance, so if your season is long enough, direct is the easier route.
| Item | Target | What happens if you miss it |
|---|---|---|
| Soil or compost temperature | 77F to 86F (25C to 30C) | Below 68F (20C) germination is slow and uneven; below 59F (15C) it stalls |
| Sowing depth | Half an inch to one inch (1 to 2.5 cm) | Too shallow and the coat dries; too deep and the seedling exhausts itself |
| Days to emergence | Five to seven days from nicked and soaked seed | Untreated seed takes two to three weeks and comes up in ones and twos |
| Seeds per station | Two in a pot, three direct | One seed per station leaves gaps you cannot fill later in the season |
| Final spacing | Two to three feet (60 to 90 cm) apart along the support | Closer than that and the laterals tangle, and mildew follows |
From seedling to planting out
Seedlings grow fast once they are up. They are ready to go out at three or four true leaves, roughly three to four weeks after sowing. Do not hold them longer than that, because a bitter melon that starts circling the pot sulks for a fortnight after planting and never quite makes up the time.
Plant out only when night temperatures stay above 59F (15C). Bitter melon is not frost hardy in the slightest, and even a cold night without frost checks it visibly, the leaves going dull and the growing tip stalling. Harden the plants off over a week of increasing time outdoors, and put the netting or frame up before the plants go in the ground so you are not threading a growing vine through a structure later.
If you have plants ready and the nights are still cool, hold them in a larger pot rather than planting. A week in a five inch (13 cm) pot in full sun costs you nothing; a week in cold ground costs a fortnight of growth.
What to write down at sowing time
Sowing is where the useful records are made, because everything later in the season is dated from it. Note the day you nicked and soaked, the day you sowed, and the day the first shoot broke the surface. The gap between those last two is the single most useful number you own, because it tells you whether your seed preparation worked or whether your propagation spot was simply not warm enough.
Also record which end of the row each plant sits at, and whether the seed came from a bought packet or from your own saved fruit. Saved seed varies a great deal in vigor from one parent fruit to another, and after two seasons of notes you will know which line to keep saving from.
- Record the soak Note the date, the water temperature and how many hours. When germination is poor the following year, this is the first thing you check.
- Record days to emergence Count from sowing to the first shoot breaking the surface. Five to seven days means your setup is right. Twelve or more means the seed was cold, not bad.
- Record the germination rate How many seeds sown, how many came up. Compare a nicked batch against an untreated one once and you will never skip the nicking again.