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Ashitaba is a perennial angelica grown for its leaves, and like most angelicas its seed dies quickly. Seed collected in the current season, kept dry and cool, germinates in useful numbers. Seed a year old is already halved, and seed two years old is usually a blank tray no matter what you do to it. If a sowing has produced nothing after six weeks in the right conditions, age is almost always the answer, and no amount of extra warmth or a second soaking will change it.
The seed is a flat papery disc with a thin wing around the edge, and it is easy to mistake empty husks for viable seed. Rub a pinch between your fingers: sound seed has a small firm kernel you can feel through the wing, while a large share of any batch is hollow. Sow two to three times as much as you think you need and expect to thin, rather than sowing thinly and hoping.
Store what you are not sowing in a sealed jar in the fridge at 35 to 40F (2 to 4C) rather than in a drawer. Warm dry air ages this seed faster than anything else. Even in the fridge, treat it as a one-season item, and plan to collect fresh seed from your own plants rather than working through an old packet.
| Seed age | Rough germination | What to do with it |
|---|---|---|
| Current season, kept cool | Good, worth sowing thinly | Sow as your main batch |
| One year, kept in a fridge | Roughly half | Sow at double density and thin |
| One year, kept at room temperature | Poor and uneven | Sow as a backup only, not as your main batch |
| Two years or older | Effectively none | Discard and source fresh seed |
Cold, light and sowing depth
In the wild the seed drops in autumn, lies on damp ground through winter and comes up as the soil warms. Copy that and germination is even. Give the seed three to four weeks at 35 to 40F (2 to 4C) in damp vermiculite or sand in a sealed bag in the fridge, then bring it into 60 to 68F (15 to 20C). Sown straight into warmth with no chilling, the same seed drags on for two months and often rots before it moves.
The seed also needs light to germinate. Press it onto the surface of damp compost and cover with the barest dusting of vermiculite, no more than an eighth of an inch (3 mm), just enough to stop it drifting when you water. Burying it a half inch (1 cm) deep is the second most common reason for failure after old seed.
The alternative to fridge chilling is to sow outdoors in a covered pot in autumn and leave it exposed to winter. This works well and skips the guesswork, but the pot must be protected from birds and heavy rain washing the surface-sown seed away. Cover it with fine mesh, sink it in a shaded spot and forget about it until spring.
- Chill the seed for three to four weeks Mix the seed into just-damp vermiculite in a sealed bag and hold it at 35 to 40F (2 to 4C). Check weekly for mold and for any seed that has already chitted, which you sow at once.
- Sow on the surface of a free-draining mix Use a mix that stays damp without going soggy, firm it lightly, and scatter the seed on top. Dust with vermiculite only. Water from below by standing the tray in shallow water so the seed is not washed about.
- Hold at 60 to 68F (15 to 20C) in bright indirect light High heat is unhelpful; anything above 77F (25C) reduces the take. Keep the surface evenly damp with a cover or a propagator lid, and vent it daily so air moves across the compost.
- Wait, and keep waiting First seedlings usually appear in 14 to 30 days, and stragglers keep coming for another month. Do not tip out a tray that looks empty at three weeks. Label it with the sowing date and leave it somewhere you will not disturb it.
The first weeks after germination
The seedling puts up two narrow seed leaves and then sits still for a fortnight, which is normal. Growth is genuinely slow at this stage and the plant is putting energy below ground before it does anything visible. The main risk in this period is damping off, so lift the cover once most of the seedlings are through, keep air moving, and water in the morning rather than the evening.
Thin to one seedling per cell or to two inches (5 cm) apart in a tray as soon as the first true leaf, which is divided and looks like a small celery leaf, has opened. Crowded ashitaba seedlings stretch and then collapse at the base. Snip the surplus at soil level rather than pulling, because the roots tangle early and pulling one lifts three.
Feed at quarter strength once the second true leaf appears, then fortnightly. These seedlings are hungry for their size but burn easily at full-strength feed. Aim for a stocky plant with short internodes rather than a tall one, and give as much light as you can without direct midday sun through glass.
Potting up, planting out and the first year
Ashitaba makes a thick fleshy taproot, so move seedlings into deep pots rather than shallow ones as soon as roots show at the drainage holes. A four inch (10 cm) deep pot, then a one gallon (4 liter) pot, gets a plant to planting-out size without the root ever circling. A root that has been coiled in a shallow module never anchors properly and the plant stays half-sized for years.
Plant out after the last frost, into rich soil that holds moisture, at 18 to 24 inches (45 to 60 cm) apart. Full sun suits cool summers; anywhere with regular days above 85F (29C) the plant is happier in afternoon shade. Set it at the same depth it grew in the pot, water it in heavily, and mulch two inches (5 cm) deep around, not over, the crown.
Do not harvest in the first year. A first-season plant is building the root that will carry every leaf you take later, and stripping it now costs you two seasons. Treat year one as an investment: water, feed, keep slugs off, and leave the leaves alone until the following spring.
Write down the collection or purchase date of the seed, the date you started chilling, the sowing date and the date the first seedling appeared. With a seed this short-lived, those four entries tell you next year whether a poor result was your method or simply an old packet.