Sowing Perilla for Seed Heads: Depth, Timing and Spacing

The seed germinates in light, so leave it on the surface

Perilla seed is a light-dependent germinator. Buried at the usual quarter of an inch (6 mm) it simply sits in the dark and rots, and the packet gets blamed. Press the seed onto damp compost, firm it so it makes contact, and either leave it bare or sift over the barest dusting no thicker than an eighth of an inch (2 to 3 mm). Light has to reach it.

The seed is also short-lived. Anything more than two years old germinates erratically, and a seed crop is one of the few plantings where that matters twice over, because the seed you save this year is what you sow next year. Sow thickly enough to allow for it and thin later rather than hoping an old packet performs.

1. Soak overnight before sowing A twelve to twenty-four hour soak in plain water softens the hard coat and pulls germination forward by several days. Drain and sow while the seed is still damp, before it dries and sticks to itself in a lump.
2. Firm the surface first Level and lightly press the compost before scattering seed, so nothing drops into a crack and buries itself. Water from below or with a fine mist, never a hard stream, or the seed washes into the corners of the tray.
3. Keep it damp for two to three weeks At 68 to 77F (20 to 25C) most seed appears in ten to twenty days. Surface-sown seed dries out in an hour on a warm windowsill, so cover the tray with a clear lid or a sheet of glass until the first seedlings show.

Germination all but stops below 59F (15C). If a spring sowing sits for a month doing nothing, it is nearly always cold compost rather than dead seed, and it will come away as soon as the tray warms up.

Sow early, because the flowering date is not yours to choose

Perilla flowers when nights lengthen past a threshold in late summer, not when the plant reaches a certain size. That single fact governs a seed crop. Whether you sowed early or late, every plant in the garden will start throwing spikes in the same fortnight, so the only variable you control is how big the plant is when that happens.

A plant sown as soon as the soil passes 59F (15C) reaches two to three feet (60 to 90 cm) with a dozen or more branch tips by the time daylength trips it, and each of those tips carries a spike. The same variety sown eight weeks later is a foot (30 cm) high with three tips, and it flowers on the same night. It is not a late crop, it is a small one.

In practice this means starting indoors four to six weeks before your last frost and setting plants out once nights hold above 54F (12C). Direct sowing works in a long season, but you lose two or three weeks of building time you cannot get back later.

Space wider than you would for leaves

A leaf crop can be crammed at eight inches (20 cm) because you are picking from the top and the plants prop each other up. A seed crop cannot. Spikes need light to set properly, they need air moving through them so the ripening seed does not mold in a wet spell, and the plants get top-heavy and lean once the heads fill.

Give each plant twelve to eighteen inches (30 to 45 cm) in the row and eighteen to twenty-four inches (45 to 60 cm) between rows. In a container, one plant to a ten-inch (25 cm) pot; two in the same pot will each give you half the spikes and both will flop.

Thin in two stages. Take the tray or drill down to about two inches (5 cm) apart once the seedlings show their first true leaves, then to the final spacing at four to six true leaves. Thinnings transplant well at that size if you lift them with a fork and water them in the same hour.

Keep the strongest seedlings rather than the tallest. A seedling that has stretched pale and thin on a windowsill will always be a weaker plant than a shorter, stockier one beside it, and it flowers at the same time regardless.

Self-sown seedlings, and why you should not rely on them

Perilla seeds itself heavily. A single plant left to shatter will give you hundreds of seedlings in the same patch of ground next spring, and they come up in a thick mat once the soil warms. Gardeners often decide to let the bed reseed itself and skip sowing altogether.

For a seed crop that is a poor trade. Self-sown seedlings appear several weeks later than a deliberate indoor sowing, they come up in a crowded clump that has to be thinned hard anyway, and they flower on exactly the same night as everything else, so they are always the small plants in the table above. Use them as a free backup, not as the main crop.

There is a second reason to control them. In parts of North America perilla has escaped into pasture and woodland edge and is treated as invasive, and it is toxic to cattle and horses. Do not let a bed reseed unsupervised, especially if there is grazing land or open ground nearby. Hoe the mat of seedlings off while they are at the seed-leaf stage, when a single pass with a sharp hoe on a dry day clears the lot.

1. Note where volunteers came up Mark the spot in your records. It tells you which plant shattered before you cut it, and it is the first place to check for seedlings the following spring.
2. Hoe at the seed-leaf stage Seedlings pull or hoe out with almost no effort while they still have only their two rounded seed leaves. Once they have four true leaves and a taproot, every one has to come out by hand.
3. Keep a few as spares Leave a dozen volunteers at proper spacing as insurance against a failed sowing or a late frost, and clear the rest. They will be smaller plants but they cost you nothing.