Growing Japanese Pepper From Seed: Fresh Seed and Seedling Care

The seed is short-lived, and that explains most failures

Japanese pepper seed has a hard, shiny, oily black coat and a very short viable life. Left to dry on a shelf it loses the ability to germinate within a few weeks, and by the following spring a batch of dried seed is usually dead. This is the single reason why so many people report that it simply never came up, and no amount of soaking, scratching or chilling brings dead seed back.

The practical consequence is that you sow it fresh, straight from a ripe berry, in autumn. Take berries from a female plant once the husks have colored and started to split, and separate out the black seeds. Do not let those seeds dry: work with them the same day, or keep them overnight in a bag of just-damp sand or coir in a cool place.

If you must store them for a few weeks, keep them damp and cool rather than dry and warm. Mixed into slightly moist sand in a closed bag at around 40F (4C), they hold far better than in a paper envelope, though sowing straight away is still much better than any storage.

The oily coat is water-repellent when fresh. Rubbing the seeds gently in a little warm water with a drop of dish soap, then rinsing them well, helps water reach the seed and improves the strike rate noticeably.

Sowing fresh seed in autumn

Sow into deep pots rather than shallow trays, because the first thing a seedling makes is a long root that hates being cut. A gritty, free-draining mix of two parts loam-based compost to one part sharp sand suits it. Set the seeds about a quarter of an inch (5 to 8 mm) deep, spaced an inch (2.5 cm) apart, and cover with a thin layer of grit to stop moss and to keep the surface from capping.

Then leave the pots outside in a sheltered spot, protected from mice and heavy rain but exposed to the cold. The seed needs a real winter, several weeks below about 40F (4C), before it will break dormancy. A pot kept warm indoors all winter will simply sit there and rot. A cold frame with the lid propped, or a shaded spot against a north wall with a wire cover, is ideal.

Germination is slow and infuriatingly uneven. Some seedlings appear in the first spring, others in the second, and a strike rate of one in three or four from fresh seed is a good result. Do not tip the pots out after one blank season. Keep them just damp through the following summer and wait.

1. Take seed from split husks only Fully ripe berries have colored and begun to split. Green or half-ripe berries give seed that has not finished developing and will not germinate whatever you do to it.
2. Clean and sow the same day Separate the black seeds from the husk, wash off the oily film, and sow immediately. Every day of drying costs you germination you cannot get back.
3. Use deep pots and a gritty mix The first root goes straight down and resents being cut or bent. Deep pots let it run and make potting up far less traumatic later.
4. Stand the pots outdoors for the winter Several weeks of genuine cold are required to break dormancy. Protect from mice with wire, keep the mix just damp, and do not bring the pots into warmth.
5. Wait two springs before giving up A significant proportion of a batch germinates only in the second year. Keep the pots labeled, weeded and lightly damp through the intervening summer.

The first year: shade, damp and no disturbance

Seedlings come up with a pair of plain seed leaves followed by small, aromatic, compound true leaves, and they are far more delicate than the adult plant looks. Keep them in bright shade for their whole first season, not full sun, and never let the mix dry out completely. A tray of small seedlings in full sun can be lost in a single hot afternoon.

Damping off is the main early risk. Sow thinly, use a gritty mix, water from below rather than over the tops, and keep air moving around them. Remove any seedling that collapses at soil level immediately, along with the mix around it, rather than hoping it stops there.

Do not feed for the first few months. Once the seedlings have four or five true leaves, a very dilute balanced feed once a month through summer is enough. Stop by late summer so the little stems harden before their first winter, which they should spend outdoors in a sheltered, frost-protected spot rather than indoors in warmth.

Potting up without killing them

This is where most home-raised plants are lost. The roots are brittle and intolerant of handling at every age, and a seedling handled roughly stalls for a season or dies outright. Pot up only when roots are showing at the drainage holes, and do it in early spring just as growth starts, never in autumn and never in the heat of summer.

Slide the whole root ball out intact and drop it into the new pot without teasing, trimming or shaking off old compost. Move up one pot size at a time. Going straight from a small pot into a large one leaves a mass of wet unrooted compost around the outside, which stays sour and rots the roots that grow into it. Water once thoroughly after potting up, then keep the plant in shade for a fortnight.

Because moving an established plant so often kills it, decide early where each one is going to live permanently. Plant it out in its second or third spring, while it is still small enough to move safely, into a position with morning sun, afternoon shade and soil that never sits wet. After that, treat the ground within three feet (90 cm) of the trunk as off limits to any spade, fork or hoe for the life of the plant.

Why you should raise several, and what to record

Seedlings are male or female, and there is no way to tell which until they first flower, typically in the third to fifth year. Raise at least five or six if you want peppercorns, so that the odds give you both sexes, and expect to remove the surplus males later. A single seedling raised in isolation has roughly even odds of being a female that can never fruit and a male that never will.

Seedlings also vary. Some are thorny and some nearly thornless, some grow twice as fast as their siblings, and the aromatic quality of the leaves differs noticeably between them. Label every pot from the day you sow and keep the labels through every potting up, because unlabelled seedlings become indistinguishable within a year.

Record the date you collected the seed, the date you sowed it, and the date each seedling emerged, since a second-year germinator is worth knowing about. Then record the year each plant first flowers and its sex, and mark that on a permanent label. That one note is the difference between a group of shrubs and a crop.