Seed Starting for Hydroponics
Seeds start in a small plug of growing medium, under light, then the whole plug drops into a net cup in the tower. No soil is involved.
Mediums
| Medium | Notes |
|---|---|
| Rockwool cubes (1″) | Cheap, standard. Needs a pre-soak: saturate in nutrient solution at pH ~5.5 until the air bubbles stop (a few minutes), drain, and don’t squeeze. Wear gloves and avoid breathing the dust; the fibers irritate skin. |
| Rapid Rooter / peat-based plugs | Easy, no pre-soak pH step; pop the seed in and keep moist |
| Coco coir plugs | Good water retention; rinse if not pre-buffered |
| Oasis cubes | Foam; works but holds a lot of water |
For a first try, rockwool or plugs are the least fiddly. Whichever you pick, it has to fit the tower’s net cups.
Step by step
- Soak the plug in pH ~5.5 solution and let the excess drain. It should be damp, not dripping.
- Sow 1–2 seeds per hole (3 for tiny seeds like lettuce, thinned later). Do not bury light-dependent seeds such as lettuce; barely cover them.
- Cover the tray with a clear humidity dome until the seeds sprout.
- Warm — most crops want 65–75 °F at the plug. In a cold garage, a seedling heat mat under the tray does more good than a space heater. Lettuce germinates poorly above ~80 °F; peppers and basil like it warmer.
- Light as soon as they sprout — take the dome off and put a light a few inches above the seedlings, 14–16 hours a day. Raise it as they grow. Too far away means stretched, leggy seedlings.
- Water from below — keep an inch of very weak nutrient solution (a quarter of the label strength, EC ~0.4–0.8) in the bottom of the tray. Do not let the plugs dry out.
- Transplant into the tower when roots show out of the bottom of the plug and the seedling has 2–3 true leaves (not counting the first pair), usually 2–3 weeks for lettuce and herbs (longer under dim light).
Germination quick reference
| Crop | Germination temp | Days to sprout |
|---|---|---|
| Lettuce | 60–70 °F | 2–7 |
| Arugula, bok choy | 60–75 °F | 3–7 |
| Kale, chard | 60–75 °F | 4–10 |
| Basil | 65–75 °F (best ~70) | 5–10 |
| Cilantro | 60–70 °F | 7–21 |
| Parsley | 65–80 °F | 12–21+ |
| Peppers | 80–85 °F | 7–14 |
| Tomatoes | 70–80 °F | 5–10 |
Staggering
Sow a few new plugs every 1–2 weeks. A tower planted all at once gives one big harvest and then nothing; staggered sowing gives a steady supply, and a spare seedling ready when a plant fails.
Troubleshooting
- Nothing sprouts — too cold, too dry, or old seed. Check the plug is damp and the temperature is within the range above, ideally mid-range.
- White fuzz or mold on the plug — too wet and too still. Vent the dome and lower the moisture.
- Seedlings fall over at the base — damping off, usually from wet, cool, stagnant conditions. Add airflow (a small fan on low) and let the surface dry a bit.
- Leggy seedlings — light too far or too weak.