Propagation Mediums

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Grodan MM40/40 Cubes (40x40x40 mm) Cubes 2250/ctn
Grodan MM40/40 Cubes (40x40x40 mm) Cubes 2250/ctn
$718.99 $881.40
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Grodan Delta 4G w/Hole (75x75x60 mm) 384 Carton
Grodan Delta 4G w/Hole (75x75x60 mm) 384 Carton
$442.99 $543.40
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Grodan Delta 4G Cubes No/Hole (75x75x60 mm) 384/ctn
Grodan Delta 4G Cubes No/Hole (75x75x60 mm) 384/ctn
$442.99 $543.40

Choosing a propagation medium

At the propagation stage you are not feeding a plant, you are keeping a cutting alive long enough to root. That means holding moisture without drowning the stem, and holding air so the new roots have something to breathe. Every product here is built around that ratio — Bio Diesel describe their coco plugs as holding the ideal air-to-water ratio for fast root development, and it is the single property that separates a propagation medium from the medium you will grow in afterwards.

Rockwool

The propagation standard, and the biggest part of this range. Grodan describe it as mineral wool made from molten basalt and limestone, spun into fibres and compressed into cubes, blocks and slabs. It is sterile and inert, holds its shape when wet, and its hydrophilic fibres wick evenly. Speedgrow's Multigrow rockwool is the sustainability option — it uses an all-natural, formaldehyde-free ECOSE binder.

Coco

The organic alternative, and easier to overwater forgivingly. Bio Diesel coco plugs come pH-buffered with a starter solution already in them, which removes the buffering step rockwool needs. Eazy-Plug coco peat trays come in 12, 24 and 77 cubes, and ROOT!T dry coco plugs come as a 24-cell tray with 60-plug refills — dry, so they store indefinitely and you wet only what you need.

Peat

Jiffy-7 pellets are the simplest thing on the page: 42mm compressed discs that you add water to and watch expand into a plug with its own netting. Sold in 30-packs and 1000-pellet cartons. No tray of loose medium to fill and nothing to mix.

Sizing, and potting on

Propagation media come in a ladder, and the point is that you move up it. Grodan's own instruction on their cubes is explicit: once roots start to emerge through the cube, plant it on into a larger Grodan block. Starting a cutting in a block far bigger than it needs is the most common way to lose one — too much wet medium around too few roots.

The ladder here runs: 40mm wrapped cubes and 38–40mm plugs to strike in, available as 12 and 30-packs or as bulk trays and cartons; then 75mm cubes with or without a hole; then 100mm Delta blocks and 150mm Hugo blocks; then crop box slabs at 370 x 550 x 150mm for running the crop out in the same material. Cubes come with a hole for a cutting or without one for seed.

How to choose

  1. Match the medium to what you grow in next. Rooting in rockwool and potting into rockwool or clay pebbles keeps one system. Rooting in coco and potting into coco does the same. Mixing families works, but it changes how you water.
  2. Pick the pack size honestly. A 12-pack of cubes suits a hobby run; the 1386-cube Grodan cartons and 1000-pellet Jiffy boxes are commercial quantities, not a starter buy.
  3. Choose hole or no hole. Cubes with a pre-formed hole are for cuttings. No-hole cubes are for seed, where you want the seed enclosed.
  4. Note what needs conditioning. Coco plugs from Bio Diesel arrive pH-buffered. Rockwool does not come pre-conditioned — follow the maker's soaking guidance before you use it.
  5. Buy the tray and the dome with it. Plugs dry out fast in open air. A humidity dome is not optional at this stage.

What else the strike needs

Medium is one of three variables. Bottom heat from a heat mat drives the strike rate, humidity from a dome stops the cutting transpiring faster than it can drink, and a rooting gel or mycorrhizal inoculant from propagation and cloning additives does the rest. If you would rather buy the combination in one box, propagation kits pairs them up. Full-size media for potting on are in grow mediums — rockwool and coco each have their own page.

Propagation Mediums FAQ's

There is no single best one — it depends on what you will grow in afterwards. Rockwool is the propagation standard because it is sterile, inert and holds its shape wet. Coco plugs are more forgiving of overwatering and often arrive pH-buffered. Peat pellets are the simplest to use. Match the propagation medium to your final medium and you make watering easier later.

Start small. A 38–40mm plug or cube is the normal size for a cutting or a seed, and the range steps up from there to 75mm cubes, 100mm Delta blocks and 150mm Hugo blocks. Too much wet medium around too few roots is a common way to lose a cutting, so size to the roots you have rather than the plant you want.

When roots start showing through the sides or base. Grodan's own guidance on their cubes is to plant on into a larger block once roots emerge. Waiting much longer leaves the roots circling inside a cube that has run out of room; moving too early disturbs roots that have not taken hold yet.

With a hole for cuttings — the pre-formed hole takes the stem without you having to push it in and damage the cut. Without a hole for seed, where you want the seed enclosed by medium on all sides. Several products here are stocked in both versions for exactly that reason, including the 75mm and Delta 4G cubes.

It depends on the material. Bio Diesel state their coco plugs contain a pH-buffered starter solution, so they are ready to use. Rockwool is not supplied pre-conditioned and is normally soaked in pH-adjusted water before you plant into it. Follow the instructions supplied with the product you buy rather than a general rule.

Size and purpose. A propagation medium is a small plug, cube or pellet sized to a tray, built to hold the air-to-water balance a rootless cutting needs. A growing medium is what fills a pot for the rest of the plant's life. Many are the same material — rockwool and coco appear in both — but you buy them in different formats.

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