Grow Guide
Weed seed germination takes 1 to 5 days when a viable seed gets three things: steady warmth of 72 to 78F, constant light moisture, and darkness. Soak or paper towel the seed until a white taproot shows, plant it a quarter to half an inch deep, root down, and keep the medium damp, never wet, until the seedling stands.
This chapter opens the grow guide because more first grows fail in the first week than at any other point. It covers the three methods that work, a day-by-day timeline, how to handle the taproot, and when to give light. What happens after the seed leaves open belongs to the stages of growth chapter.
What does a weed seed need to germinate?
A cannabis seed needs warmth, water and oxygen, in that order of importance. Warmth between 72 and 78F tells the embryo to wake up. Water softens the shell and starts the taproot. Oxygen keeps the root alive, which is why a seed drowned in a glass for a week rots instead of sprouting. Light is not required and does not help.
Temperature is the number most growers get wrong. Below 65F germination slows to a crawl and the seed may rot before it opens. Above 85F the embryo cooks. Seed labs germinate hemp under controlled cycles between 68 and 86F; Oregon State University's hemp extension program covers seed quality and viability testing for growers who want the full protocol. For a home grower, the middle of that range is the target, and a seedling heat mat with a thermostat set to 75F is the cheapest insurance you can buy.
Moisture means damp, not soaked. If you can squeeze water out of the paper towel or the soil, it is too wet. Old, cracked or warm-stored seeds germinate slowly or not at all, so a five-year-old pack from a drawer deserves lower expectations than a fresh one from the fridge.
Paper towel vs direct sow vs starter plugs
Three methods work. Each has a place.
Paper towel. Fold a plain white paper towel, wet it, wring it out, lay the seeds inside, and put it between two plates in a warm dark spot. Check twice a day. When the taproot is a quarter inch long, plant. You can see what is happening and sort duds before they take up a pot. It also gives you the most chances to damage the root.
Direct sow. Plant the dry seed a half inch deep in pre-moistened, lightly packed soil or coco, cover it, and mist the surface. Nothing touches the taproot and the seedling never gets transplanted. The cost is that you cannot see progress, so a dead seed sits in a pot for a week before you know. Direct sow is what I recommend for anyone growing in soil with a fresh pack.
Starter plugs. Rapid Rooters, Jiffy pellets and rockwool cubes hold moisture and air in the right ratio by design. Soak the plug, drop the seed in the hole, pinch it closed, and keep the tray warm under a humidity dome. Best for hydro growers and anyone starting more than a handful of seeds. Rockwool needs a pH 5.5 soak first; the others do not.
How long to germinate weed seeds in paper towel?
Most seeds show a taproot in 24 to 72 hours in a paper towel at 75F. Fresh seeds from a reputable breeder often crack within a day. Older or poorly stored seeds can take 5 to 7 days. If nothing has happened by day 10 and the seed is still hard, it is finished; if it has gone soft and brown, it rotted.
Do not give up at day 3 or keep hoping at day 14. Between those points, keep the towel damp, warm and dark, and check it morning and night.
Germination time chart: day by day
Day-by-day germination timeline at 72 to 78F, paper towel method then soil
| Day | What you should see | What to do |
|---|---|---|
| 0 | Dry seed in a damp towel | Warm, dark, check moisture |
| 1 | Seed swells, shell may split | Nothing; leave it alone |
| 2 to 3 | White taproot 1/8 to 1/4 inch | Plant root down, 1/4 to 1/2 inch deep |
| 3 to 5 | Seedling loop breaks the surface | Move under gentle light |
| 5 to 7 | Round seed leaves open, shell drops | Light 18 hours, mist only |
| 7 to 10 | First true serrated leaves | First light watering around the stem |
| 10 to 14 | Second set of true leaves | Seedling stage has begun |
Handling the taproot and when to give light
Once the taproot shows, you have a fragile thing. Handle the seed by the shell with clean tweezers or fingertips, never by the root. Make a hole in damp medium with a pencil, drop the seed in root down, and cover loosely. If the root has curled, plant it curled; do not try to straighten it. A taproot that has grown into the paper towel fibers should be cut free with the fibers still attached rather than pulled.
Give light the moment the seedling loop breaks the surface. Before that, light does nothing. After that, a seedling without light stretches into a pale thread in 24 hours and never fully recovers. Start with a low-power LED or a fluorescent tube 18 to 24 inches above the tray for 18 hours a day. A full-strength flowering light is too much for a seedling in its first week, so dim it or raise it. The indoor growing chapter covers light setup.
The mistake most growers make with germination
The mistake is drowning the seed. Growers soak seeds in a glass for days, plant into soil that runs water out the bottom, and then water again because the surface looks dry. The seed rots, or the seedling damps off at the soil line and falls over. The second most common mistake is digging the seed up to check on it, which snaps the root.
Water the medium before you plant, then do not water again until the top inch is dry, which in a small pot at 75F is usually three to five days. If you have to look, look at the towel, not the soil. In eighteen years of Dear Danko letters, "my seeds never came up" almost always ended with "and I kept it nice and wet."
Next step: the seedling stage
Once the first true leaves appear, germination is done and the seedling stage begins: the plant switches from seed reserves to roots, and your job switches from patience to light and water discipline. Get the first two weeks right and you avoid the pale, drooping seedlings covered on the yellow leaves page. Cultivation is for adults where it is legal; check your local law before you start seeds.
Sources
- Oregon State University Extension: Hemp (top-level hemp resource page; used as the reference for seed quality and germination testing context behind the 72 to 78F range)
