Sowing New Zealand Spinach: Soaking the Hard Seed and Getting Even Germination

What you are actually sowing

The thing in the packet is not a seed in the usual sense. It is a hard, knobbly, corky capsule about the size of a peppercorn, with several true seeds locked inside it. That capsule is built to survive months in dry ground and salt spray, and it does its job well: dropped straight into a seed tray it can sit for four weeks before anything appears, and a good part of it may never appear at all.

Because each capsule holds more than one seed, you can also get two or three seedlings crowding out of a single sowing point. That is normal and not a sign of contamination. It does mean you should plan to thin, and it means counting capsules rather than counting expected plants when you work out how much to sow.

The uneven emergence is the part that trips people up. A row sown on one day will come up over a fortnight, not over three days. If you write the row off after ten days and dig it over, you will be digging out seedlings that were about to appear. Mark the row clearly and give it a full month before you decide.

Buy or save more capsules than you think you need. A germination rate of half to two thirds is normal even with good treatment, and that is the crop behaving as designed rather than a bad packet.

Soaking and warmth

Two things fix germination: water into the capsule, and soil above 60F (16C). Soaking is not optional here in the way it is with peas. An unsoaked capsule in ordinary garden soil takes a long time to wet through, and every extra day in the ground is another day for soil organisms to get into it.

Soak in plain water at room temperature for twenty-four hours, changing the water once partway through. Some growers go to forty-eight hours with a change every twelve hours, which helps in very dry stored seed. Do not go past two days: the water goes sour, the capsule ferments and you lose the lot. Sow the same day you drain them, because a swollen capsule that dries out again is worse off than one never soaked.

Soil temperature does the rest. Below 55F (13C) the capsule sits and rots. At 60F (16C) you get emergence in two to three weeks, ragged. At 70 to 75F (21 to 24C) it comes up in ten to fourteen days and much more evenly. Read the soil two inches (5 cm) down in the morning for three days running rather than going by how warm the afternoons feel.

1. Soak twenty-four hours Put the capsules in a cup of room-temperature water and leave them a full day, changing the water once. They will darken and feel slightly softer. Drain in a sieve and sow immediately; do not leave drained capsules on a windowsill overnight.
2. Scratch the very hard ones Any capsule still bone hard and unchanged after a day can be rubbed briefly on medium sandpaper to break the corky surface, then soaked another two hours. Do not try to crack it open; the seeds inside are easily damaged.
3. Wait for 60F (16C) soil Take a morning reading at two inches (5 cm) depth. Hold off until it stays above 60F (16C) for three consecutive mornings. Sowing early into cold ground loses more capsules than any other single mistake.
4. Keep the surface damp until it is all up Because emergence runs over two weeks, the bed has to stay evenly moist for that whole period. A light covering of fine compost or a piece of hessian over the row until the first seedlings show keeps the surface from crusting.

Depth, spacing and how much room to leave

The capsule is large and well provisioned, so cover it properly. Half to three quarters of an inch (1 to 2 cm) is right. A shallow sowing dries out during the long germination period, which is precisely the failure you are trying to avoid. Firm the soil over the row with your palm so the swollen capsule is in contact with damp soil all round.

Spacing is where people go badly wrong, because they space it like true spinach. This plant does not stand up in a neat rosette; it sprawls flat and wide, sending trailing stems out in every direction, and one mature plant covers a circle two to three feet (60 to 90 cm) across by late summer. Sow stations eighteen inches (45 cm) apart and thin to a single plant at each, with two to three feet (60 to 90 cm) between rows.

Three or four plants will keep a household in cooked greens right through the hot months, which is far fewer than the same area of true spinach would need. It is genuinely better to sow a short row and let each plant run than to sow a long dense row and fight it all summer.

Thin by cutting the weaker seedlings off at soil level with scissors. Capsules produce clustered seedlings whose roots are tangled from the start, and pulling one lifts the others with it.

Starting in pots, and what to write down

Where the season is short, starting in pots is worth doing, and this crop transplants more willingly than most sprawling plants because it is moved before it starts running. Sow two soaked capsules into a three inch (8 cm) pot, keep it at 70F (21C), thin to one seedling and plant out once nights hold above 50F (10C) and the seedling has four or five true leaves.

Handle the rootball gently and plant at the same depth it grew in the pot. A seedling that checks badly will sit sulking for a fortnight, which is a real cost on a crop that is already slow to start. Water it in well and keep it moist for the first two weeks while it takes hold.

This is also the point to start a record, because germination here is the part that varies most from garden to garden. Note the date you sowed, the morning soil temperature on that day, how long you soaked, and the date the first and last seedlings appeared. After two seasons those numbers tell you your own sowing point precisely, which no packet instruction can.

1. Log the soak length and the soil temperature Write down how many hours you soaked and what the soil read at two inches (5 cm) on sowing day. These two numbers explain almost every difference in how a row of this crop performs.
2. Log first and last emergence Record the day the first seedling showed and the day the last one did. A spread of more than three weeks means the soil was still too cold; a spread of a week means you got it right.
3. Mark where each plant sits Push a labeled stake in beside each thinned plant. The stems will have covered the ground by midsummer and you will not otherwise know where the crown is when you need to water or feed it.