Harvesting Perilla Seed Heads: Three Stages, Three Short Windows

One spike, three products, and none of the windows are long

A perilla spike changes fast. It emerges as a tight green column of unopened buds, then flowers from the bottom upward over about a week, then the lowest seed hardens while the top is still in flower, and finally the whole spike turns brown and starts shedding. Three of those moments are worth picking, and each lasts only a few days.

This is why a seed crop needs to be looked at every two or three days from late summer, not once a week. All the plants flower within the same fortnight, so the windows arrive on the whole planting at once, and a spike missed at the bud stage is already at the next stage by your following visit. Walk the row with a container in hand rather than deciding to come back later.

Judging the stage by touch, not by looks alone

From a distance a bud spike and a spike with its first flowers open look nearly identical, because the flowers are small and pale. Get close and run the spike between finger and thumb. At the bud stage it feels uniformly firm and slightly rough, like a small green cone. Once flowering starts the bottom inch feels softer and looser, and you can see two or three open flowers if you turn the spike over.

The green seed stage is the easiest to feel. Squeeze the lower third of the spike gently. If the little swellings there give slightly and feel like soft grain, the seed has set but is still tender. Once they resist the squeeze and roll under your thumb like grit, the seed has hardened and that window has closed.

Full ripeness announces itself by sound. Tap a brown spike over your palm and ripe seed drops out immediately. If seed falls at a tap, the whole planting is at that stage and needs cutting within a day or two.

1. Check the same three plants each visit Pick three plants at different points in the row as your indicators. Checking the same ones every time makes small changes obvious in a way that a general glance across the bed never does.
2. Work in the morning Spikes are firmest and least brittle after a cool night and before the sun has been on them. A ripe spike handled at midday sheds far more seed on the way to the kitchen than the same spike cut at dawn.
3. Keep the stages separate Use a different container or a different corner of the tray for each stage as you cut. They are not interchangeable once mixed and sorting them afterwards is tedious.

Spikes on the outside of the plant and at the top run ahead of those lower down and in the shade by three or four days. Pick over the plant rather than clearing it in one pass, and you effectively stretch each window.

Ripe seed shatters, so cut into something

The one hard rule of a perilla seed crop is that you never move a ripe spike through open air. The seed sits loosely in a dry calyx and drops at the slightest knock, so a spike snipped and carried across the garden arrives with a fraction of its seed still on it, and the rest is now sown in your path.

Hold a paper bag or a deep tray under the spike with one hand and cut with the other, so the head falls straight into the container. For a whole plant, slide a large paper bag over the top of the plant, close it round the main stem, and cut the stem below the bag. Turn the bag upright and everything that shatters on the way is caught.

Do not use plastic bags for anything you are storing. Ripe spikes still hold moisture in their stems, and in a sealed plastic bag they sweat and go moldy within a day. Paper breathes, and a paper bag hung somewhere dry and airy for a week or two doubles as the drying stage.

1. Cut low, cut whole stems At full ripeness, take entire branches rather than individual spikes. Fewer cuts means fewer knocks, and the branch gives you something to hold while the head goes into the bag.
2. Hang the bag to finish drying Two weeks somewhere dry, airy and out of direct sun. The stems must snap rather than bend before you thresh, or the seed will not store.
3. Thresh in the bag Once dry, close the bag and rub or shake it hard. The seed collects in the bottom; the stems and empty calyxes stay on top and lift out by hand.
4. Winnow the last of the chaff Pour the contents from one bowl to another in a light breeze or in front of a fan on its lowest setting. The seed is heavy enough to fall straight down and the chaff blows aside.

Store cleaned seed dry, dark and cool in a paper envelope or a jar with a desiccant sachet. Perilla seed is oily and loses viability fast; sowing seed is worth using within two years, and anything held longer should be sown thickly on the assumption that half of it is dead.

Clear what you did not pick, before it drops

Whatever is left standing at the end of the season will shed thousands of seeds where it stands. A single mature plant produces far more seed than any garden needs, and in parts of North America perilla has escaped from gardens into pasture, roadsides and woodland edge, where it is treated as an invasive weed and is toxic to grazing livestock. Clearing the remainder is part of the harvest, not an optional tidy-up.

Cut the plants down while the heads are brown but before they are shedding freely, bag them at the moment of cutting exactly as above, and take the bags away from the bed. Do not drag whole plants across the garden or leave them on a compost pile that does not get hot; either scatters seed as effectively as leaving them standing.

Then check the ground. Go over the bed the following spring while any seedlings that did escape are still at the seed-leaf stage, when a single hoeing on a dry day clears them. Left to reach four true leaves they each need pulling by hand, and a bed that has shattered can take two seasons to bring back under control.