Grodan Delta 4G Rockwool Cube with Hole – 75x75x60 mm for Hydroponic Transplants

What is the Grodan Delta 4G Rockwool Cube with Hole used for?

The Grodan Delta 4G is a sterile rockwool cube designed for transplanting seedlings or rooted cuttings into hydroponic systems. Its unique fibre structure balances water and oxygen to support strong root development in the veg stage before moving to slabs or systems like NFT, flood & drain, or drippers.

What size is the Grodan Delta 4G cube, and what plugs fit in the hole?

The cube measures 75mm x 75mm x 60mm and has a pre-drilled hole that fits most standard starter plugs (around 25–40mm). It accepts 1" rockwool cubes, Root Riot, Eazy Plug, or similar—just ensure a snug fit without crushing the plug.

Can I use the Grodan Delta 4G cube for seeds or clones?

Both. It’s most commonly used for transplanting rooted clones or seedlings, but you can start seeds directly in the cube if needed. However, most growers start in a smaller plug first, then step up into the Delta 4G cube for better root development.

Do I need to pre-soak the Grodan Delta 4G cube, and how?

Yes—pre-soak in pH-adjusted water (typically around 5.5–6.0). Many growers use a mild nutrient solution for the soak. Soak until fully saturated, then let it drain naturally—don’t squeeze it, as that compresses the air pockets needed for healthy roots.

How should I water plants in the Grodan Delta 4G cube?

Keep the cube moist but not soaked. Rockwool holds water well, so overwatering is a common issue. Let the surface dry slightly and use lift weight or feel to gauge moisture. Bottom watering works well, or let your system (drippers, NFT) handle it gently at first.

Does the Grodan Delta 4G cube contain nutrients, and what EC should I feed?

No—it’s an inert medium. Feed with a mild nutrient solution suitable for young plants, then increase EC as roots develop. Rockwool works best with clean, soluble feeds. Organic nutrients can be used cautiously, but thick formulas may clog systems.

Which hydroponic systems is the Grodan Delta 4G cube compatible with?

It works with NFT channels, flood & drain (ebb & flow), drippers, or as a stepping stone onto rockwool slabs. Just adjust your watering frequency early to avoid oversaturating young transplants with small root zones.

Does the Grodan Delta 4G cube grow algae or attract pests?

It can if the top stays wet and exposed to light. Algae itself isn't deadly but may reduce oxygen and attract fungus gnats. Use covers or collars to block light, improve airflow, and avoid overwatering the surface.

Can I transplant a starter plug into the Grodan Delta 4G cube?

Yes—that’s exactly what it’s designed for. Insert the plug deep enough for stability and good contact, but avoid burying the stem. Covering the hole lightly can help reduce algae, but ensure air can still circulate.

Why are my plants stalling or roots not growing in the Grodan Delta 4G cube?

Common causes include overwatering, cold root zones, or incorrect pH. Ensure the cube is moist but not saturated, maintain warm temps, and monitor feed strength. If the cube dries out, re-wet slowly and thoroughly to avoid dry pockets.

Can I reuse or compost Grodan Delta 4G cubes?

Reusing isn’t recommended due to salt and pathogen buildup. Grodan cubes aren’t compostable like organic media, so dispose of them according to local waste guidelines. Some growers repurpose dried cubes for non-edible projects or drainage layers.

Can I use the Grodan Delta 4G cube for indoor or outdoor growing?

Yes—indoors, it’s common in hydro systems or semi-hydro setups. Outdoors, protect from direct sun and wind as it can dry quickly and grow algae. You can also transplant from rockwool into coco or soil, with careful moisture management during the transition.

Is the Grodan Delta 4G cube safe and easy to handle?

It’s sterile and safe for food crops. Rockwool can be dusty or slightly irritating—if handling large quantities or cutting, gloves and a mask are recommended. Store dry cubes in a clean area to keep them sterile until use.

Do I need a humidity dome or bottom heat with Grodan Delta 4G cubes?

For cuttings, a humidity dome helps during early rooting. If transplanting an already-rooted plug, a dome usually isn’t needed. Bottom heat can help root development in cooler environments but isn’t essential in warm grow rooms.

Do I need runoff, and how do I manage salt buildup in Grodan cubes?

Yes—some runoff helps prevent salt buildup. If you see white crusting or unstable pH/EC, it may be time for a light flush. Avoid daily flushing—aim for consistent, balanced feeding with occasional corrective flushing when needed.