Gadenin日本語Get the appThe seed needs light, so do not cover it
Shiso, sold in English-speaking countries as perilla, is a light-dependent germinator. The seed will not break dormancy in the dark, so the usual habit of covering seed to twice its own depth is exactly what kills a shiso sowing. Press the seed onto the surface of damp compost and leave it there, or sift over the barest dusting, no more than an eighth of an inch (2 to 3 mm), which is thin enough for light to reach it.
This is the single most common reason a packet fails. Sown at a quarter of an inch (6 mm) the germination rate collapses to almost nothing, and the gardener blames old seed. Sown on the surface and kept damp, the same packet will give you far more seedlings than you have room for.
- Firm the surface first Level and lightly firm the compost before sowing so the seed sits on a flat surface and does not fall into cracks. Seed that slips into a crevice ends up buried and stays dormant.
- Press, do not bury Scatter the seed thinly and press it down with a flat palm or a small board so each seed is in contact with damp compost. Contact matters more than covering.
- Cover the tray, not the seed Instead of soil, use a sheet of clear glass or a clear lid to hold humidity. It keeps the surface from drying while still letting light through. Remove it the moment the first seedlings show.
If you are sowing outdoors and worried about the seed washing away, cover with a thin layer of coarse sand or fine grit rather than soil. Light still reaches the seed between the grains.
Soak the seed and expect a slow start
Shiso seed has a hard coat and germinates slowly, typically ten to twenty-one days, which is two to three times as long as most annual herbs. Gardeners give up and dig the tray over on day ten, a week before anything was going to happen. Soaking the seed in water overnight, eight to twelve hours, softens the coat and pulls several days off that wait.
Temperature decides the rest. The soil wants to be at 68F (20C) or better; below 59F (15C) germination becomes erratic and can stop altogether. Sowing early into cold spring soil does not give you an early crop, it gives you rotted seed.
| Soil temperature | Days to emerge | What to expect |
|---|---|---|
| Below 59F (15C) | No reliable emergence | Seed sits and often rots; wait |
| 59 to 68F (15 to 20C) | Eighteen to twenty-five | Patchy and uneven, but it comes |
| 68 to 77F (20 to 25C) | Ten to fourteen | The reliable range; sow here |
| Above 82F (28C) | Ten to fourteen | Fast but the surface dries out too quickly |
Trays indoors or straight into the ground
Both work. Trays give you control over the surface moisture, which is the difficult part, and let you start four to six weeks before the last frost. Direct sowing avoids the root disturbance that checks a young shiso for a week or more, but the surface of open ground dries fast and the seed goes with it.
- Sowing in trays Use a fine seed-starting mix, sow on the surface, and water from below by standing the tray in an inch of water until the surface darkens. Watering from above washes surface-sown seed into corners.
- Sowing direct Wait until the soil is reliably above 68F (20C) and all frost has passed. Sow a pinch of seed every eight inches (20 cm), press in, and keep the top half inch damp until they show.
- Transplant at two true leaves Move tray seedlings into individual pots once they have two true leaves beyond the seed leaves. Handle them by a leaf, never by the stem, which is thin enough to crush.
- Harden off before planting Give indoor-raised plants a week outside in increasing light and wind before planting out. Straight from a windowsill into full sun and the leaves scorch pale within two days.
Thinning and final spacing
Shiso comes up in a thick mat because the seed is small and hard to sow thinly. Thin in two passes rather than one: the first pass at the seed leaf stage to about an inch (2 to 3 cm) apart, the second at three or four true leaves to the final spacing. Thinning to full spacing straight away leaves you with nothing if slugs take a few.
Final spacing depends on whether you want big plants or a lot of small ones. A well-pinched plant given room will fill a two foot (60 cm) circle by late summer.
| Growing method | Spacing between plants | Notes |
|---|---|---|
| Bed, one big plant | Sixteen to twenty inches (40 to 50 cm) | Pinched hard, gives the longest picking season |
| Bed, cut-and-come-again | Six inches (15 cm) | Smaller plants, more of them, quicker to finish |
| Container, ten inch pot | One plant per pot | Two crowd each other and both stay small |
| Window box | Eight inches (20 cm) | Expect to water daily in high summer |
Thinnings are worth eating. Shiso seedlings at the seed leaf stage carry the full scent of the adult plant and are a genuine crop in their own right, not waste.
When nothing comes up
Before you re-sow, work through the causes in order. In practice almost every failure is one of the first three, and re-sowing without fixing the cause simply repeats it.
- The seed was covered Scrape back the top quarter inch of a small area and look. If you find plump, unchanged seed sitting below the surface, it was buried. Re-sow on the surface.
- The surface dried out Seed that swells and then dries dies. If the top of the compost went pale at any point during those two weeks, that is your answer. Cover the tray with glass next time.
- It was too cold Push a thermometer into the compost in the morning rather than trusting the air temperature. Morning soil is often ten degrees colder than the afternoon air suggests.
- You gave up too early Leave the tray for a full four weeks before you write it off. Late, straggling germination is normal for this plant, and a tray that looked dead at day fourteen is often full at day twenty-two.
Write down the date you sowed and the date the first seedling showed. Two seasons of that record tells you more about your own conditions than any packet instruction, and you will stop re-sowing prematurely.