How to Germinate Weed Seeds: Method, Realistic Timings, and What a Failure Usually Means

Soak the seeds in room-temperature water for twelve to eighteen hours, then move them into damp paper towel inside a closed container held at roughly 22-25°C in the dark, and check once a day. Most viable seeds crack and show a white taproot somewhere between 24 and 96 hours; anything still closed at day seven is usually a problem with conditions rather than with the seed, and anything still closed at day ten is generally finished.

That is the whole method. The rest of this article is about the parts people get wrong — the temperature they never measured, the potting mix that was too wet, the seedling that opened fine and then stalled for a fortnight — and about when the New Zealand calendar means you should be doing this at all.

Why paper towel beats planting straight into mix, for most people

You can drop a seed 10 mm deep into damp seed-raising mix and it will very often come up. Commercial nurseries do exactly that with vegetables. The reason I still recommend paper towel for a first grow is not that it works better — it is that it gives you information. In a container you can see the taproot on day two. In a pot you see nothing for five days, and if nothing appears on day six you have no idea whether the seed is dead, drowned, too deep, too cold, or perfectly fine and just slow.

When you are germinating three or five seeds that cost real money, visibility matters more than the marginal risk of handling. Once you have done it a few dozen times and trust your mix and your temperature, direct sowing is less fuss and skips one transplant shock entirely.

The one genuine argument against paper towel is handling damage. A taproot longer than about 10 mm gets fragile and sticky, and towels with a strong embossed pattern grip the root hairs. Use plain, cheap, unpatterned paper towel, and move seeds into mix while the root is short.

The method, step by step

• Soak. Room-temperature tap water in a glass, seeds in, somewhere dark. Twelve hours is plenty; eighteen is the sensible outer limit. Past about 24 hours you are starving the embryo of oxygen.
• Drain. Tip the water off. Seeds that sank are not automatically better than seeds that floated — floating is mostly about trapped air on the shell, and plenty of floaters germinate fine.
• Wrap. Two sheets of paper towel, wet then wrung out so it is damp rather than dripping. Seeds spaced a couple of centimetres apart, towel folded over.
• Enclose. Into a takeaway container, a zip bag, or between two plates. The point is to stop evaporation, not to make a greenhouse.
• Warm and dark. 22-25°C. Hot water cupboard, on top of a fridge, near a heat pump outlet — anywhere with a stable, mild warmth.
• Check once daily. Once. Opening it six times a day dries the towel and chills the seeds.
• Plant at 5-10 mm of taproot. Root pointing down, 10 mm deep in damp mix, covered loosely. Do not press it in.

What the clock actually looks like, day by day

Fresh, well-stored seed in good conditions is fast. Here is what I expect, and what each stage tells you.

• Day 1-2: the shell splits and a white tip appears. This is the ordinary case for healthy seed at the right temperature.
• Day 3-4: the remainder of a normal batch catches up. A seed cracking on day four is entirely normal and will usually grow into a plant indistinguishable from its faster siblings.
• Day 5-7: late but not lost. Older seed, harder shells, or a container sitting at 18°C rather than 23°C. Keep going.
• Day 8-10: unlikely. If the towel has stayed damp and warm the whole time, this seed probably is not coming.
• Beyond day 10: stop. Continuing to wait mostly means waiting for mould.

Once planted, expect the seedling to break the surface in two to four days. A cracked seed that goes into mix and never emerges has almost always been planted too deep, planted into mix that was saturated, or dried out in the top centimetre on a warm afternoon while you were at work.

The published germination rate for any particular cultivar we sell is listed on its genetics report — the Digweed Feminised genetics report is a good example of the format — rather than being a single number that applies across the catalogue.

Temperature is the variable that fails silently in a New Zealand house

Most germination failures I hear about in this country are temperature failures, and they are invisible because nobody measured. A living room in Christchurch in September sits comfortably at 20°C while you are home with the heater running, and drops to 11°C by 6 am. A seed spending eight hours a night at 11°C is not dead — it is just slow, and it will read as a failure to anyone who gives up at day five.

Buy a cheap digital thermometer with a min/max memory and put it next to the container overnight. That single measurement resolves more germination arguments than anything else. Wooden villas in Wellington and Dunedin swing hard; a modern insulated home in Hamilton barely moves.

Where to actually put it:

• Hot water cupboard. The classic, and usually good, but some run at 28-30°C on the top shelf. Measure first and use a lower shelf if it is hot.
• On top of the fridge. Gently warm and remarkably stable. My default.
• Seedling heat mat. Reliable, but the cheap ones without a thermostat can push a container past 30°C. Put a folded tea towel between mat and container.
• Not a sunny windowsill. Direct sun cooks a sealed container and the temperature swings 15 degrees in an afternoon.

Too hot is a real failure mode, not a theoretical one. Above roughly 30°C germination rates drop and rot becomes likely. If the seeds smell sour when you open the container, heat and moisture have got away from you.

When a seed opens and then the seedling stalls

This is the more frustrating failure, because the germination worked. The taproot came out, the seedling stood up with two round cotyledons, and then for ten days absolutely nothing happened. No new leaves, no height, sometimes a faint yellowing.

Three causes account for nearly all of it.

Overwatering

A seedling has a root system a few centimetres across. Put it in a three-litre pot of saturated mix and the roots sit in an anaerobic zone with nowhere to grow. The plant looks droopy, you read droopy as thirsty, you water again. Start seedlings in small containers — a 250 ml cup with drainage holes, or a jiffy pellet — and water a splash at a time around the stem. The mix should be damp, and should lighten noticeably in weight before you water again.

Feeding too early

The seed carries its own food for the first week to ten days. Full-strength nutrient solution on a three-day-old seedling burns root tips and the plant stops while it repairs. Plain water until the first true leaves are properly out, then start at roughly a quarter of the label rate. If you want to sanity-check strengths for your setup, the nutrient dosing calculator is a reasonable starting point.

Not enough light, or far too much

A seedling on a kitchen bench in ambient room light stretches into a pale thread and stalls. The same seedling 15 cm under a full-power 200 W LED bleaches. Seedlings want bright, indirect light or a dimmed light at 40-60 cm. If the stem is stretching more than about 3 cm before the first true leaves, it needs more light or the light needs to come closer.

Damping off is the fourth cause and the ugliest — the stem pinches and goes brown right at soil level, and the seedling topples. It is a fungal problem driven by wet, still, cool mix. There is no fixing an affected seedling. Prevent it with a small fan moving air in the room, mix that is damp rather than soaked, and by not crowding pots together.

When to start, given the season runs the other way here

Almost every germination guide online is written for the Northern Hemisphere and tells you to start in March or April. Reverse it. In New Zealand the outdoor season runs from spring through to autumn, seedlings go outside once the last frost has passed — around October in most of the country — and harvest lands through March and April.

Working back from that, germinate indoors in late August to mid-September and grow the seedlings under a light or on a bright windowsill for four to six weeks before they see the outdoors. That gives a plant with a real root system going into the ground, which matters enormously for how it handles a Wellington southerly or a Canterbury nor'wester in November.

The margins are different at the two ends of the country. In Northland and the Bay of Plenty you can be a fortnight later and still finish comfortably. Inland Canterbury, Central Otago and Southland get frost from April, which means the harvest date is not negotiable and a late start simply removes flowering weeks from the end of the season. Germinating in November in Alexandra is how people end up cutting immature plants in a hurry.

Here is the season laid out month by month, which is the clearest way to see where germination sits relative to everything else.

Timings shift with latitude — the north runs earlier and longer than inland Otago and Southland.

Autoflowers change the arithmetic. Because they flower on age rather than daylight, you can germinate them from October right through to early January in the warmer north and still get a finish, and you can run two cycles in a season. That flexibility is the main reason to look at autoflowering seed varieties if your spring got away from you.

How storage before germination decides half the outcome

Seeds are alive, and they age. A seed kept cool, dark and dry stays viable for years. The same seed left in a hot car for an afternoon, or in a bathroom drawer through a humid Auckland February, loses viability quickly and quietly — it will still look identical.

• Cool and stable. A sealed container in the fridge is ideal. Avoid the freezer unless the seeds are genuinely dry, because ice crystals damage the embryo.
• Dark. Light degrades seed over months.
• Dry. Humidity is the main killer in northern New Zealand. A silica sachet in the container costs almost nothing.
• Let them warm before opening. Take a container out of the fridge and open it immediately and condensation forms on the seeds. Leave it sealed on the bench for a few hours first.

What a seed looks like matters less than people think. Dark, tiger-striped and hard is the textbook ideal, but pale seeds germinate all the time and a mottled shell tells you very little. The one meaningful visual test is pressure: a seed that crushes or gives under firm fingernail pressure was empty or immature. Do not test seeds you intend to grow.

What germination rates actually mean, and why three out of five is not a fault

No seed line germinates at 100 percent, and a batch where one of five does not open is within ordinary variance. That is not a satisfying answer when you only bought three, which is why I suggest germinating one or two more than you intend to grow if you have the room. Spares also let you cull the weakest seedling rather than being stuck with it.

Genuine seed faults do exist and they look distinct from environmental failure. The tell is the pattern. If every seed in the batch sits closed at day eight in a container you measured at 23°C, that points at the seed. If two opened in 36 hours and three did nothing, temperature and moisture were fine for all five and the three were simply not viable. If none opened and you never measured temperature, the fault is the measurement.

Our germination guarantee and returns policy sets out how this is handled — the practical point is that documenting conditions as you go, particularly temperature, makes any conversation about it straightforward.

If you are choosing seed for a first attempt, hardy, well-established genetics are more forgiving of a slightly cold hot water cupboard than a temperamental exotic. These three are all robust starters, and the cards show current flowering times and listing details.

Choosing what to germinate before you germinate it

The decision that matters more than technique is what is in the towel. Outdoors in New Zealand the constraint is autumn: it arrives damp rather than dry, and botrytis in dense late-flower buds is the defining risk, worse in Northland, Auckland and the Bay of Plenty, easier through Gisborne, Hawke's Bay, Nelson and Marlborough. A variety with open bud structure and a fast finish beats a heavier yielder that is still packing on weight in late April.

Finishing time is therefore the number to check first. Indoors it is a scheduling preference. Outdoors south of about Christchurch it decides whether you harvest at all. Browsing cultivars suited to outdoor growing with that filter in mind saves a lot of grief in March.

It helps to see how flowering times spread across a category rather than looking at one listing in isolation.

1254 of 1254 varieties in this category publish a flowering time. Counted from the catalogue when this page was built.

Two cultivars worth putting side by side for a first outdoor season are M-39 and Chemo — different structures, different finishing behaviour.

If you would rather answer a few questions than read listings, the strain finder tool narrows the catalogue by region and season length.

Common questions from New Zealand growers

Do I need to use bottled or filtered water?

No. New Zealand tap water is fine for germination almost everywhere, and the chlorine levels in reticulated supply are far too low to matter over a twelve-hour soak. If you are on tank water, it works equally well. The only water worth avoiding is anything that has sat in a hose in the sun, which can be well over 30°C and carry algae.

My seed cracked but the root is growing upwards. Have I ruined it?

Not at all. Roots find down on their own within a day or so. Plant it root-tip-down if you can do it without touching the root itself — tweezers on the shell, never on the root — and if it went in sideways, leave it. The seedling will sort itself out.

Can I germinate in winter and grow indoors year-round?

Yes, and indoors the season is irrelevant — you set daylength with a timer. The practical winter issue in New Zealand is cold, not light: a garage or sleepout in July can sit below 15°C overnight, which stalls seedlings badly. If you are running a tent through winter, sort out heating before you germinate, and start with varieties selected for indoor growing that stay manageable in height.

How long should I wait before giving up on a slow seed?

Ten days in warm, consistently damp conditions. Before you call it, verify the towel has never dried out and the temperature has actually been in the low twenties overnight as well as during the day. Most seeds people write off at day five would have opened at day seven.

Is it worth scuffing or nicking the shell?

Rarely, and it is easy to do damage. If a seed has soaked and sat in warm damp towel for seven days without a crack, very lightly abrading the edges between two pieces of fine sandpaper is a reasonable last attempt on a seed you would otherwise discard. Never cut into the shell with a blade, and never scarify a seed that has not already had a fair chance.

If something in your setup does not match anything described here, the frequently asked questions page covers ordering and delivery details, and there is more on seedling care and early growth across the growing articles archive.