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Rockwool starter cubes

Choose rockwool starter cubes by block size, planting hole and the number of plants you want to raise. Our range includes Grodan with a 38 mm hole, Agra Wool with 28 or 38 mm holes, and unbranded 4 × 4 × 4 cm cubes. Agra Wool is available individually or in boxes of 224.

6 products

Start with the size of your propagation plug

Measure your plug’s width or diameter and height before choosing a starter block. For 7.5 × 7.5 × 6.5 cm blocks, the planting hole is the key fit measurement. Choose 28 or 38 mm to suit the actual plug; identical outer dimensions do not mean every plug will fit. Browse our propagation plugs for young plants.

Agra Wool: one block size, two planting holes

FeatureSmall holeLarge hole
Block dimensions7.5 × 7.5 × 6.5 cm7.5 × 7.5 × 6.5 cm
Hole diameter28 mm38 mm
Hole depth35 mm35 mm
MaterialBasalt fibre with Ecose binderBasalt fibre with Ecose binder
Pack optionsIndividual or box of 224Individual or box of 224

A small cube or a starter block with a planting hole?

For moving a plug into a larger root block: choose a 7.5 × 7.5 × 6.5 cm starter block. The Grodan block in this selection has a 38 mm planting hole. Agra Wool offers 28 and 38 mm holes with the same outer dimensions. Check the fit without compressing the plug or block.

For smaller cubes in larger quantities: the unbranded rockwool cubes measure 4 × 4 × 4 cm and come in a bag of 1300. They differ in size from the starter blocks with 28 or 38 mm holes. Check tray fit and the connection to any larger block separately.

For the quantity you need: choose Agra Wool individually or in a box of 224 blocks. Compare the current pack price with the number of plants you plan to raise. Looking for other growing medium formats? Browse rockwool and other fibre growing media.

Grodan starter block, 4 cm unbranded cubes and Agra Wool starter blocks with planting holes
  • Grodan
  • Agra Wool

Preparing starter blocks and managing irrigation

Wet the block evenly before use and allow excess water to drain. For initial saturation of Grodan, use a suitable nutrient solution with a pH of 5.5–6.5. Agra Wool Speedgrow can be wetted with tap water for the initial preparation. Adjust subsequent feeding and irrigation to the crop, growth stage and measured conditions.

Position the block so excess water can drain away. Check moisture and root development regularly. There is no single water dose or timer setting that suits every starter block and plant. Check your solution with a pH meter and EC meter. Read why measuring pH and EC matters.

Move the young plant when roots have developed through the block and the plant is ready for its next growing position. When moving to a larger growing medium or a hydroponic system, check dimensions, support and drainage in your own setup.

Choosing nutrients for the next growing stage

Atami and B’cuzz advice

Rockwool starter cube questions

Need help choosing a starter block?

Tell us your plug dimensions, growing medium and number of plants. We can help you choose a suitable starter block and pack size.

  • Compare plug size and planting hole

  • Choose the number of blocks and pack

  • Discuss preparation and irrigation

Ask for advice

Continue your propagation setup