Troubleshooting Soil Blocks

Every grower presses a bad batch now and then — blocks that crumble, blocks that won't let go, a tray gone green. Nearly all of it traces to one variable: moisture. Too dry and blocks crumble or stick; too wet and they slump. Find your symptom below; the fix is usually one batch away.

Frequently Asked Questions

Why are my blocks falling apart?

The mix is usually too dry or under-packed rather than missing an ingredient. Add more water until a squeezed clump releases a drop, and pack harder when filling the blocker — a firm pass with your fingers followed by a second pass with the heel of your palm. Most crumbling blocks simply weren't packed firmly enough. A good hands-on check: lifting the bottom tray to eject should never take more effort than squeezing a lemon. If it does, that's the mix telling you it's too dry before the blocks even hit the tray.

Why are blocks sticking in the blocker or won't release?

This is usually the opposite problem — the mix is too wet. If blocks won't eject cleanly, hold back some dry mix while batching and stir it back in. Also dip the blocker in water before every press; a dry blocker grips the mix instead of releasing it.

Why does my mix stick to the top plate during ejection?

This usually happens if you sow seeds directly into the bottom tray before pressing the blocks out and skip the vermiculite step. The clay in the mix turns sticky once it's wet, and without a light coating of vermiculite over the tray, it clings to the top plate — pelleted seed makes this especially noticeable. Always sprinkle vermiculite over the tray after placing seeds and before pressing the blocks out.

Why are my blocks drying out too fast?

Blocks have more exposed surface area than plug trays. See Watering for a bottom-watering routine that keeps blocks consistently moist.

Why do I have mold or algae on top of my blocks?

This almost always means the blocks are staying wet too long. Let them follow a daily wet-to-dry cycle — water in the morning and let them dry out somewhat by the next day — rather than keeping them constantly soaked, and make sure your tray isn't holding standing water.

Why didn't my seeds germinate?

The most common reason is poor seed-to-soil contact — a seed sitting in a tiny air pocket inside the dimple won't germinate even in moist soil. Press each seed firmly into its dimple so it's touching soil on all sides, then top-dress with vermiculite rather than more mix. If seeds still don't come up, double check soil temperature and light needs for that variety; some seeds need light to germinate and shouldn't be buried at all.

What is damping off, and how do I prevent it?

Damping off is a fungal disease that rots seedlings at the soil line shortly after they come up, and once a seedling is infected it can't be saved — prevention is the only real fix. Overwatering is the single biggest cause, so bottom-water and let blocks dry out somewhat between waterings rather than keeping them constantly wet. Airflow matters too: don't overcrowd blocks, and vent humidity domes daily rather than leaving them sealed throughout germination. Some growers prevent damping off by keeping everything sterile (clean trays, sterile mix, treated water); others build a living, compost-based mix whose own beneficial microbes outcompete the fungi that cause it. Both approaches work — just don't mix a sterile setup with a living-compost ingredient and expect either benefit.

Still stuck? Re-read the mix page — nine problems in ten started in the wetting. Or write to us — we make these tools and we use them.