How to Grow Shiso From Seed | A Fast Guide

Shiso is a warm-season annual grown for its edible, aromatic leaves. Starting it from seed indoors is more reliable than direct sowing, since germination can be finicky. Getting the depth, warmth, and moisture right from the start makes the difference between a full tray of seedlings and a frustrating wait.

Whether you’re growing green or red varieties, the same principles apply. The seeds need light to germinate, steady warmth, and a head start before the outdoor growing season begins.

Why Start Shiso Seeds Indoors

Starting shiso indoors 4–8 weeks before the last frost gives the plants a real head start, and it protects the seeds from the cold soil and unpredictable weather that hampers direct sowing. Shiso is cold-sensitive, and frost will kill young plants outright.

Seeds germinate best with consistent warmth around 70°F (20°C). A heat mat placed under the tray provides this steady bottom heat. Cover the tray with a humidity dome or plastic wrap to hold moisture in until sprouts appear, then remove the cover right away so air can circulate.

Expect germination to take anywhere from 4–7 days to 2–4 weeks depending on conditions. Sowing extra seed helps, since shiso germination is naturally inconsistent.

How to Sow Shiso Seeds Step by Step

Shiso seeds need light to germinate, so the planting depth is critical. Burying them too deeply is one of the most common mistakes gardeners make.

1. Soak the seeds in room-temperature water for 12–24 hours before planting to soften the seed coat and speed up germination.
2. Fill trays with a moist seed-starting mix and press it down gently to remove air pockets.
3. Sow seeds on the surface or very shallowly, pressing them into the soil so they make good contact. Do not cover them with a layer of mix.
4. Mist the surface to settle the seeds, then cover the tray with a humidity dome or plastic wrap.
5. Place the tray on a heat mat set to about 70°F (20°C), in a spot with bright, indirect light.
6. Keep the mix evenly moist — never soggy and never dry. Check daily, as the surface can dry out quickly.

Once sprouts appear, remove the cover and move the tray into strong light. Seedlings that don’t get enough light grow leggy and weak. If you started shiso for its leaves, you might want to check out our roundup of the best shiso leaf seeds to buy for reliable germination and strong varieties.

Transplanting Shiso Seedlings Outdoors

Move shiso seedlings outside only after the last frost has passed and nighttime temperatures stay reliably above 45–50°F (7–10°C). Even a light frost can kill the plants.

Harden off the seedlings first. Over 7–10 days, set them outside for a few hours each day, gradually increasing their time in the open air and direct sun. This step prevents transplant shock and sun scald.

Shiso grows into a bushy plant, and crowding invites disease from poor air circulation.

Soil, Sun, and Water Needs

Shiso thrives in fertile, well-drained soil that holds moisture, rich in organic matter, with a pH around 5.5–6.5. Work compost into the bed before transplanting to give the plants steady nutrition.

Give shiso full sun to partial shade — at least 6 hours of direct sun. In hot climates, afternoon shade keeps the plants from stressing and bolting. Water at the base of the plant to keep foliage dry and reduce disease risk, and keep the soil evenly moist but never soggy.

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