A pellet is a compressed disc of media in a fine mesh that expands into a plug when soaked. The point of both is the same: a seedling can be planted without ever being pulled out of anything, which matters for crops that sulk after root disturbance such as cucumbers, squash and beans.
The choice between them is partly horticultural and partly about where the material comes from.
The comparison
| Measure | Peat pellets | Coir pellets |
|---|---|---|
| Source material | Harvested peat bog | Coconut husk, a by-product |
| pH | Acidic, often limed by the maker | Close to neutral |
| Water holding | High and even | High |
| Rewetting once dry | Difficult, water runs off | Easy |
| Starter nutrient included | Usually not | Often, check the label |
| Mesh around the plug | Usually present | Usually present |
| Environmental cost | Significant, peatland carbon | Low, uses a waste stream |
| Salt content on arrival | Low | Can be high if poorly washed |
The rewetting problem is the practical one
Peat is hydrophobic when it dries. A tray of Jiffy 36 mm Peat Pellets, 100 Count ($11.95) left one warm afternoon too long will shed water off the surface rather than absorb it, and getting it back takes standing the whole tray in water for a long soak. Coir does not do this to anything like the same degree, which in a bright spring greenhouse is worth more than any small difference in water holding capacity.
Gro-Med Organic Coco Coir Seed Starter Pellets, 35 mm, 50-Pack rewet readily and arrive with nutrient already in the plug, which covers the first fortnight before you need to start feeding. Check the label though, because a plug already carrying fertiliser is not what you want under very small or slow seed.
The mesh
Most pellets of both kinds are held in a fine mesh net. That net is what stops the plug falling apart, and it is also the thing to look at before planting out. Nets vary from readily degradable to stubbornly persistent, and a root passing through a mesh that does not break down is a genuine constriction. Either buy a product that states the net degrades, or slit the net with a fingernail as you plant.
Where a pellet is the wrong choice
Pellets are small. A tomato that needs to hold in the propagation house for six weeks will outgrow one long before planting out, and potting on from a pellet into a larger pot is no easier than potting on from a cell. For crops with a long transplant period, a soil block or a deeper cell serves better. Pellets are at their best for crops that go from sowing to planting quickly and hate being disturbed.
The decision, summarised
- Cucurbits, beans, sweetcorn and anything that resents disturbance: either, and a pellet beats a cell for all of them.
- Peat-free by preference or policy: coir, without any horticultural sacrifice worth naming.
- A greenhouse you cannot check daily in spring: coir, because a dried peat pellet is very hard to bring back.
- Very fine seed, or crops sensitive to salt: a fine seed-starting mix in a cell rather than a nutrient-charged pellet.
- Long holding period before planting out: a soil block or a deeper cell, not a 35 mm pellet.
