Tomato seeds usually fail to germinate for one of seven reasons: the soil is too cold (below 50°F / 10°C they barely sprout at all), the seed tray dried out, the seeds were planted too deep, the mix stayed soggy and the seeds rotted, the seed was old, or you simply have not waited long enough. Check soil temperature first — it is the cause in most indoor failures.
Diagnose It in 2 Minutes
Work through this table before you throw anything away. Find the row that matches what you see, then read the matching fix below.
| What you see | Most likely cause | Quick check |
|---|---|---|
| Nothing after 14 days, seeds firm and pale when dug up | Soil too cold | Soil thermometer at seed depth reads below 65°F (18°C) |
| Nothing after 14 days, seeds soft, dark or mushy | Rotted from too much water | Mix smells sour; tray has standing water |
| Seeds sprouted, then seedlings fell over at the base | Damping off (fungus) | Thin, pinched stem at soil level |
| A few sprouted, most did not | Old or poor-quality seed | Packet is 4+ years old, or stored warm/humid |
| Seeds sprouted under the surface but never broke through | Planted too deep | Seeds were buried more than 1/4 inch (6 mm) |
| Tray surface dried to a crust between waterings | Dried out mid-germination | Top inch of mix is dry and hard |
| It has only been 5–7 days | Not enough time yet | Tomato seeds take 6–14 days; cold soil stretches this to 21 days |
1. Soil Too Cold — the Most Common Cause
Tomatoes are a warm-season crop. Their seeds germinate best at 75–90°F (24–32°C) and will not germinate at all below about 50°F (10°C). Between 50–65°F they may sprout eventually, but slowly and unevenly — two to three weeks instead of one.
The trap indoors is that room temperature is not soil temperature. A tray on a cool windowsill, in a basement or a garage can sit 5–10°F below the air temperature, especially overnight. That is enough to stall a whole tray.
Fix: Measure the soil, not the air. Push a soil thermometer (a kitchen probe works) to seed depth in the morning for two days running. If it reads below 65°F, move the tray somewhere warmer or put it on a seedling heat mat set to 75–80°F. Remove the mat once most seedlings are up — it is for germination, not growing on. Our temperature chart lists the exact range for tomato and 30+ other vegetables.
2. Seeds Dried Out
A tomato seed must absorb water to switch germination on. If the mix dries out after that process has started, the embryo dies — and re-wetting will not revive it. This is the most common failure in small cells and peat pots, which dry from the edges in a day.
Fix: Water the mix thoroughly before sowing so it is evenly damp like a wrung-out sponge, sow, then cover the tray with a clear lid or plastic wrap until seedlings emerge. Check daily by touch: the surface should feel damp, never dusty. Once seedlings are up, take the cover off the same day so air can circulate.
3. Too Wet — Seeds Rotted Before Sprouting
The opposite mistake is just as deadly. In saturated mix there is no air in the pore spaces, and the seed cannot breathe. It rots instead of sprouting — soft, dark and often with a sour smell. Garden soil in a tray makes this worse: it holds water, crusts over and drains poorly.
Fix: Always use a fresh, fine seed-starting mix, never garden soil. Water from below or mist gently, and make sure trays drain freely — never leave them standing in water. If the mix is soggy, let it dry until damp before re-sowing, and start a fresh batch rather than waiting on rotted seed.
4. Planted Too Deep
Tomato seeds are small, with very little stored energy. Planted more than 1/4 inch (6 mm) deep, many run out of energy before they reach the surface — or rot in the damper mix down there. Tomato seeds do not need light to germinate, but they do need to be shallow.
Fix: Sow 1/4 inch deep at most — about twice the seed’s own width. A good rule is to press the seed into the mix and cover it with just a fine dusting of mix or vermiculite. Mark the depth on a dibber or your fingertip so every cell is the same.
5. Old or Poorly Stored Seed
Tomato seed keeps better than most vegetables — often 4–6 years when stored cool, dry and dark — but it still declines. Seed kept in a warm, humid shed, or a packet opened and left loose for a season, can drop sharply in germination rate. Parsnip and onion seed fail far faster; tomato is forgiving, but it is not immortal.
Fix: Before re-sowing a whole tray, test the packet. Put 10 seeds on a damp paper towel, fold it into a labelled zip bag left slightly open, and keep it warm (75–80°F). Check daily. If 7 or more sprout in 14 days, the seed is fine and the problem is your setup. If fewer than 5 sprout, buy fresh seed — no fix will rescue a dead batch.
6. You Have Not Waited Long Enough
At the optimal temperature, tomato seeds sprout in 6–14 days. In cool soil that stretches to 14–21 days. Many gardeners dig up or discard a tray on day 7 that would have sprouted on day 12.
Fix: Compare against the packet’s stated range and your soil temperature, not against the calendar. Wait the full 14 days at warm temperatures — 21 if the soil has been cool — before deciding the batch failed. While you wait, do the paper-towel test above with spare seed: it tells you whether the seed is alive without disturbing the tray.
7. Damping Off After Germination
Sometimes the seeds do germinate, then the seedlings collapse at soil level a day or two later, with a thin pinched stem. That is damping off, a fungal problem (often Pythium) that thrives in cool, wet, still air — especially in reused mix or dirty trays.
Fix: Prevention is the cure. Use fresh mix, clean trays, remove the humidity cover as soon as seedlings emerge, give bright light and gentle airflow (a small fan on low, or an open window nearby). Water in the morning so the surface dries during the day. Seedlings already fallen over cannot be saved — re-sow in fresh mix.
How to Re-Sow Tomatoes Successfully
- Use fresh seed-starting mix, moistened before sowing.
- Sow 1/4 inch deep, 2 seeds per cell (thin to the strongest later).
- Keep soil at 75–80°F with a heat mat or a warm spot, measured with a thermometer.
- Cover until emergence, then uncover immediately and give 14–16 hours of bright light.
- Water only when the surface starts to dry; never leave trays standing in water.
- If nothing appears in 14 days at warm temperatures, test the seed and start again — the second sowing is usually the one that works.
Frequently Asked Questions
How long do tomato seeds take to germinate?
Usually 6–14 days at 75–90°F soil temperature. Below 65°F it can take 14–21 days, and below 50°F they may not germinate at all.
Can I use old tomato seeds?
Often yes — tomato seed stored cool and dry can stay viable for 4–6 years. Test 10 seeds on a damp paper towel first; if fewer than half sprout, buy fresh seed.
Do tomato seeds need light to germinate?
No. Tomato seeds germinate in darkness, which is why they are covered with mix. Seedlings need bright light immediately after they emerge, though.
Why did my tomato seeds germinate and then die?
That is usually damping off — a fungus in cool, wet, airless conditions. Use fresh mix, remove the cover once seedlings emerge, and give airflow and light.
Should I soak tomato seeds before planting?
It is optional. A short soak of a few hours can speed up germination slightly, but it is not necessary, and soaking overnight can damage seed. Correct temperature and steady moisture matter far more.
