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Starting Seeds in Grodan

The most important thing when using Grodan stone wool is that you need to saturate the product fully before using it. When you don’t fully saturate it, some of the stone wool can stay dry and will be hard to get wet at a later stage (hydrophobic). A way to check if the product is fully saturated is to weigh the product and it should be above a certain weight. As an example a Grodan Delta DM6G Grow Block of 10 x 10 x 6.5 cm (4” x 4” x 2.5”) has a volume of 650 ml, so in theory if it is completely filled with water it should weigh 650 grams. However, there will always be air in the Grodan rock wool so we take a water content (WC) of about 85% after initial saturation, meaning the Grow Block should be approximately 550 grams or slightly greater.

I recommend using nutrient solution at 5.5 pH when saturating the product so that nutrients are immediately available for the plant. For the germination itself nutrients are not needed, so some people saturate the plugs with just water and then add the nutrient solution immediately following germination. However, fairly quickly after germination nutrients are needed for further development. So to sure it is easier to saturate the plugs with nutrient solution. Most growers use 1/2 rate nutrient solution for starting then full rate at transplant.

Below are characteristics of some of the most common types of Grodan used in hydroponic production.

 

Grodan AO cubes 25/40 10/10

AO cubes are recommended for lettuce, herbs, and other greens in a raft system as the tapered base makes it easier to fit into the raft faster.

AO-cubes

AO 25/40 mm (0.98 x 1.58 in)
L25 x W25 x H40 mm
200 (20 x 10) cubes per pad
Grodan-ao-cubes6,000 cubes per case
30 pads per case

 

Top = 25 mm
Bottom = 19 mm
Height = 40 mm
Hole = 10 x 10 mm
Weight dry (1 cube) = 2 g
Weight saturated (1 cube) = 18 g
Also available:  AO 36/40 = 1.5 in; 98 cubes/pad; 2,940 cubes/case
AO 50/40 = 2 in; 50 cubes/pad; 1,500/case

 

Grodan AX cubes 25/40 10/10

AX cubes are recommended for lettuce, herbs, and other greens in a NFT system as the wider base gives the plug more stability in the gutter.

Grodan-ax-cubes

AX 25/40 mm (0.98 x 1.58 in)
L25 x W25 x H40 mm
200 (20 x 10) cubes per pad
AX-cube6,000 cubes per case
30 pads per case


Top = 19 mm
Bottom = 25 mm
Height = 40 mm
Hole = 8 mm (1/4)
# per pad 200 (20 x 10)
Weight dry = 2 g
Weight saturated = 18 g

 

Grodan Kiem Plugs in French Trays

Grodan-kiem-plugs-in-french-trays

Grodan-kiem-plugs-in-french-trays-individual

Kiem Plugs in French Trays
# per tray = 240 (12 x 20)
Height = 2.1 cm
Dry weight = 1 g
Kiem Plugs
Height = 2.1 cm
Weight dry = 1 g
Weight saturated = 9 g

 

Grodan Block Delta DM4G

Grodan-block-delta-dm4g

DM4G
7.5 x 7.5 x 6.4 cm (3 x 3 x 2.5 in)
Weight dry = 25.3 g each
Weight saturated = 273 g each
Volume = 368.7 cubic centimeters
85% WC = 313.4 g

 

Grodan Block Delta DM6G

Grodan-block-delta-dm6g

DM6G
10.2 x 10.2 x 6.4 cm (4 x 4 x 2 1/2 in)
hole = 1.5/1.6 in (36/40 mm)
Weight dry = 45.6 g each
Weight saturated = 494 g each
Volume = 655.5 cubic centimeters
85% WC = 557.2 g

 

Grodan Block Delta DM9G

Grodan-block-delta-dm9g

DM9G
15 x 10 x 6.5 cm (6 x 4 x 2.5 in)
two holes
Weight dry = 67-73 g
Weight saturated = 879 g
Volume = 975 cubic centimeters
WC 85% = 828.8 g

 

Grodan Grotop Expert Slab

grodan-grotop-expert-slab

Grotop Expert
100 x 20 x 7.5 cm (39.4 x 7.9 x 3 in)
(99 x 19 x 7.8 cm)
Weight dry = 753 g

 

Grodan AX 25/40 cube with lettuce roots and stem post-harvest.
Grodan AX 25/40 cube with lettuce roots and stem post-harvest.

Also available from Hort Americas:

Grodan Block Delta DM9G 27 x35 top right (144/case)

Grodan Block Delta DM6G 20×15 1 hole

Grodan Block Delta DM6G 27×35 2 hole

Grodan Block Delta DM4G 20×15 (384/case)

Grodan Block Delta DM4G 27×35

Grodan Cube AO 36×40 15/15 hole

Grodan Cube AO 36×40 10/10 hole