Rockwool blocks for transplanting, 4 to 15 cm
Regular price
3,50 €
Regular price
Sale price
3,50 €
Unit price
/
per
| Format | Price | Price per unit | vs Bloc de 10 cm, lot de 10 |
|---|---|---|---|
| Cube de 4 cm, lot de 15 | 3,50 € | 0,23 € | −69 % |
| Bloc de 7,5 cm, lot de 10 | 5,50 € | 0,55 € | −27 % |
| Bloc de 10 cm, lot de 10 | 7,50 € | 0,75 € | — |
These Grodan rockwool blocks take over from the seedling stage. The 4 cm cube takes the seed or cutting, then the rooted plant moves into a 7.5 or 10 cm block with a hole, which is then placed on a slab or in a gutter. A 15 cm block, sold individually, completes the range.
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The summary
- Four formats: Grodan rockwool cubes and blocks, from 4 to 15 cm.
- How the sizes follow on: seedling in a 4 cm cube, then transplanting into a drilled block.
- Preparation: a soak in water adjusted to between pH 5.5 and 6, then draining without squeezing.
- Which pack: 15 cubes of 4 cm, 10 blocks of 7.5 or 10 cm, or a single 15 cm block.
Four sizes of rockwool to take a plant from seedling to system
Grodan rockwool blocks take a plant from seedling to system: 4 cm cubes by 15, pre-drilled 7.5 or 10 cm blocks by 10, 15 cm blocks sold singly. Soaked at pH 5.5 to 6, they go into a Grodan Vital slab, an NFT channel or an aquaponic raft.
In soilless growing, a plant changes container as it grows, without its roots ever being disturbed. Grodan rockwool lends itself to this progression: the seed or cutting starts in a small cube, then the whole cube is set into a larger block, which in turn goes into a slab or a system. The fibres, made from spun basalt rock, are sterile and inert: they bring neither disease nor nutrients, and leave your nutrient solution in sole charge of feeding.
📏 From cube to block
Before use, you soak the cubes and blocks until completely saturated in water adjusted to pH 5.5 to 6, at 18 to 20 °C. As new rockwool contains no salts, its starting conductivity is zero: in hydroponics, this first soak is therefore done in a light nutrient solution, at 1.5 to 3 mS/cm for lettuces. You then let the blocks drain naturally, without squeezing them, because crushed rockwool loses the air pockets that the roots need. The rooted plant, with its cube, is then slipped into the hole in the block, and the whole thing is placed on a rockwool slab, in an NFT channel or on an ebb-and-flow table, depending on the size chosen.
4 cm cube
It receives the seed or cutting at the start and is sold in a row of 15 cubes.
7.5 cm block
Pierced at the top and sold in packs of 10, it holds the small rooted cube of lettuces and herbs.
10 cm block
Sold in packs of 10, it carries tomatoes, peppers and cucumbers until they are placed on a slab.
15 cm block
The largest size, sold individually, offers the greatest root volume before planting out.
Smaller seedling cubes for starting plants in numbers
To start a whole tray of lettuces, 2 cm rockwool cubes, supplied in sheets of 150, are ideal for densely sown seedlings. Once they have germinated, the plants move into the 7.5 cm blocks without being repotted, so you keep a single medium from seedling to harvest.
Rockwool that is never squeezed or allowed to dry out
A compressed block loses its air, and a block that dries out completely is hard to rewet. Let it drain on its own after soaking, water it before it becomes too light, and wear gloves when handling or cutting dry rock wool.
💧 Air and water in the block
In a Grodan Delta block, the fibres are mostly oriented vertically, which gives it its stability and distributes water evenly from top to bottom. Pores of varying sizes hold water in the finest ones and let air circulate in the larger ones, while grooves under the block prevent water from stagnating at its base. The recommended working range is between 55 and 80% water by volume: you water when the block drops towards the bottom of this range, to bring it back up to 80%. The simplest approach is to weigh it: a saturated 4 cm propagation block weighs about 64 g, and it is time to water when it falls to around 50 g. A block watered from below rewets by capillary action, without compacting the fibres.
🥬 The lettuce example
Lettuce shows well how a crop grown in rockwool unfolds. The seeds germinate in 1 to 3 days at 15 to 18 °C, then the seedlings spend 8 to 18 days in propagation, at 18 to 21 °C by day and 13 to 16 °C at night. During this phase, the watering solution does not exceed 1.8 mS/cm with overhead watering, or 2.5 mS/cm on an ebb-and-flow table, and its pH stays between 5.5 and 6. The young lettuces then go into production for 15 to 21 days, with their block set on the system. This schedule serves as a guide for other salad crops and for herbs, which follow a similar rhythm.
🐟 Blocks in aquaponics
In aquaponics, rockwool blocks are best suited to systems without a gravel bed: NFT channels, rafts and flood-and-drain tables. Placed in a slotted net pot, your block holds the seedling while its roots grow down into the fish water. Once soaked and rinsed, rockwool does not alter the water chemistry, which makes it safe for the fish, but it holds moisture for longer than clay pebbles. For seedlings intended for the system, soak them in water simply adjusted for pH or in water from the tank, rather than in a fertiliser solution that would end up in the fish circuit. Also rinse new blocks before placing them, so that loose fibres do not reach the pump. The article which grow medium to choose in aquaponics compares these supports.
Technical specifications
The sizes
- 4 cm cube
- 40 x 40 x 40 mmSeedlings and cuttings, row of 15
- 7.5 cm block
- 75 mm square, perforatedTransplanting young plants
- 10 cm block
- 100 mm square, perforatedFruiting vegetables before placing on bread
- 15 cm block
- 150 mm per sideSold individually
Application
- Material
- Basaltic rock woolSterile and inert, zero conductivity when new
- Preparation
- Soaking at pH 5.5 to 6Water at 18 or 20 °C, then drain without squeezing
- Working moisture level
- 55 to 80% by volume4 cm block: about 64 g when saturated, water at around 50 g
- Systems
- Bread, NFT, tide, drippers
In the box
- 15 cubes of 4 cm, 10 blocks of 7.5 or 10 cm, or 1 block of 15 cm, depending on the pack chosen
Preparation, working moisture, weight and lettuce schedule based on the Grodan Delta brochures and "Three stages of lettuce growing"; sizes based on the distributor's data sheet.
Documents & manuals
Grodan Delta brochure
Structure of Delta blocks, working moisture range and watering. Manufacturer's document, in English.
The three stages of lettuce in rockwool
Soaking, germination, propagation and growing of lettuce, with pH, conductivity and block weights. Grodan guide, in English.
Document not showing? Some publishers block display inside a frame, so open it in a tab.
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Frequently asked questions
6 questions
6 key questions
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