Watering

Soil blocks have no walls, so water them from below — never from above. Set the tray in three-quarters of an inch to an inch of water for a minute or two, let the blocks drink, then drain what's left. Blocks should cycle from wet to nearly dry between waterings; soggy around the clock is the one state they can't forgive.

How do I bottom-water soil blocks?

• The simple soak. Set the block tray in a solid tray holding ¾″–1″ of water and give it 1–2 minutes — the blocks wick what they need. Pour off any standing water. For most setups this is the whole routine, two to three times a week.
• The pour-in. With blocks in a solid tray, pour water down the tray's edge or an open channel with a narrow-spout can — never a sprinkler rose, which dissolves blocks where it lands. Drain the excess once the tops darken.
• The nested-tray trick. If your blocks sit in a mesh tray inside a solid one, tilt the mesh tray up, fill the solid tray, and lower the blocks back into it. Refill until they stop drinking, then drain.
• The hands-off option. A capillary mat under the tray wicks continuously; blocks take only what they need.

How often should I water?

Check daily — blocks expose more surface than plastic cells and dry faster, especially under lights. Size sets the pace: 0.9″ blocks can want water once or twice a day, while big 2″ blocks with good airflow may go several days. Don't water by the calendar; water when the tops of the blocks look dry. Many growers water each morning and aim for blocks that are nearly dry again by the next — that daily wet-to-dry cycle is what keeps mold and algae away.

Should I mist or dome blocks while they germinate?

Yes. Before germination, keep the surface consistently moist with a fine mist and a humidity dome, re-misting daily until sprouts show. Germination is rarely even, so it's fine to leave the dome on until most of the tray is up — but lift it once a day to let the blocks breathe. A sealed, sweating dome is one of the fastest routes to damping off.

What happens if blocks stay soggy?

Green algae, white fuzz, fungus gnats, and — worst — damping off, the stem rot that fells seedlings overnight. All of them are the same message: too wet for too long. Drain standing water, add airflow, and let the cycle swing dry. More in Troubleshooting.