Why Growers Reach for Grodan A-OK Plugs in Stone Wool
A-OK is the propagation plug the rest of the Grodan range is built around, and this is the shrink wrapped version of it. Part number 298490 is the wrapped carton, and a single sheet is available as 298490-S. The plug measures 1.4 x 1.4 x 1.6 in, under the format code 36/40, even though the name says 1.5 in. The arithmetic confirms it: 98 plugs sit in a seven by fourteen grid, which comes to 9.8 by 19.6 in and clears a 10 by 20 flat. Stone wool is spun from molten rock and compressed, giving a fibre structure that is mostly air by volume while still holding water against gravity. The fibres run largely vertical, which is what keeps the plug in one piece when you lift it out of a tray by the shoulders. Density and water distribution are consistent plug to plug, and that uniformity is the whole argument for a manufactured plug over a hand-filled cell. The shrink wrap matters more than it sounds, because the printed label sits on it and a wrapped sheet survives being moved around a shelf. Unwrapped cartons exist as part number 293824 and cost less per plug, but they arrive as loose sheets. Anyone sowing one tray at a time is better served by the single sheet.
Working With 1.5 Inch Rockwool Cubes From Seed to Block
Condition the sheet first, because stone wool comes out of the factory on the alkaline side. Soak it in pH adjusted water, let it drain, and only then drop in a seed or a cutting. That single step is the difference between a clean first week and a week spent chasing a lockout. Match the pH your base feed runs at. Each cell tapers toward the base, so roots stay put and a sheet tears apart cleanly when the time comes. Keep irrigation light and frequent while the root is still inside the plug. Over-watering a young plug is the commonest way to stall one, since the fibre will hold far more than a seedling can drink. Most rooms move on after one to two weeks, pressing the plug into the dibble hole of a larger block. The plug sits slightly proud of the block face if you push it too shallow, and that exposed shoulder is where algae starts. A single sheet suits a hobby room or a trial of a new variety; the case is for anyone running a tray a day.
Key Features
- Shrink wrapped sheet: Keeps the sheet together and carries the printed sowing instructions.
- Sold two ways: One sheet of 98, or the full carton of thirty sheets.
- 36/40 format: The plug is 1.4 x 1.4 x 1.6 in, not a true 1.5 in.
- Fits a 10 by 20 flat: The seven by fourteen grid clears a standard propagation tray.
- Uniform density: Water, nutrient and pH spread evenly from one plug to the next.
- Vertical fibre structure: The plug holds its shape when lifted and keeps block contact tight.
- Tapered cell: Roots stay in their own plug so sheets separate without tearing.
- Condition before use: Soak in pH adjusted water, since stone wool is alkaline as made.
Technical Specifications
| Specification | Value |
|---|---|
| SKUs | 298490 for the case, 298490-S for a single sheet |
| Brand | Grodan |
| Line | A-OK Starter Plug, stone wool |
| Format code | 36/40 |
| Nominal size | 1.5 in |
| Actual plug dimensions | 1.4 x 1.4 x 1.6 in |
| Plugs per sheet | 98, in a seven by fourteen grid |
| Sheets per case | 30, giving 2,940 plugs |
| Packaging | Shrink wrapped sheets, label printed on the wrap |
| Tray fit | Standard 10 by 20 flat |
| Material | Stone wool |
| Fibre orientation | Predominantly vertical |
| Preparation | Soak in pH adjusted water before sowing |
| Unwrapped alternative | Part number 293824, sheets loose in the carton |
| Barcode | 774783495932 (single sheet) |
