Step 3 - Seed Starting
Peat vs Coco Coir for Seed Starting
They perform similarly enough that this is largely a values decision. The handling differences are real, though, and worth knowing first.
Janet H. - the hands-on owner behind Janet Media Group.
Published - last updated
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Both work. Both hold water well, both are low in nutrients, and both repel water when bone dry. If germination rate is your only criterion, this is not a decision worth agonizing over: buy whichever your local store stocks, and wet it thoroughly before sowing.
| Sphagnum peat | Coconut coir | |
|---|---|---|
| Source | Harvested from peat bogs | By-product of coconut processing |
| pH | Acidic, so commercial mixes add lime | Close to neutral |
| Water holding | High | High, and rewets more readily |
| Rewetting when dry | Difficult, water runs off | Easier, though it still needs patience |
| Nutrient content | Essentially none | Essentially none, may carry some salts |
| Structure over time | Breaks down gradually | Holds structure slightly longer |
| Environmental objection | Bog extraction and carbon release | Shipping distance and processing water |
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Top pickEspoma Organic Seed Starter MixFine, low-nutrient starting medium | Most seed trays | 8.9 | Check price on Amazon |
| 2 |  Jiffy Peat Pellet Seed Starter GreenhouseCompressed pellets in a domed tray | The least fuss possible | 8.0 | Check price on Amazon |
| 3 |  Burpee Self-Watering Seed Starting KitCell tray, dome and watering mat in one box | First-time seed starting | 8.4 | Check price on Amazon |
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Scores are our own editorial judgment, formed from published specifications and independent sources. They are not aggregated customer ratings, and they are not the result of hands-on testing, which we do not currently do. See how we choose.
The handling differences that matter
Peat is acidic, which is why commercial seed mixes add lime to bring it toward neutral. If you are mixing your own from raw peat and not adjusting it, that acidity can slow some crops. Coir arrives close to neutral and needs no adjustment at all.
Coir usually comes as a compressed block that expands enormously with water. Check the ratio on the packet, because it is easy to end up with far more medium than you planned for. Peat comes loose in a bag and needs no preparation beyond wetting.
Both repel water when completely dry, and that catches people out. Wet the medium in a tub until it holds together like a wrung-out sponge, then fill the cells. Watering a dry tray from above washes small seeds out of position and leaves dry pockets in the middle of each cell.
The salt question with coir
Coir is processed from coconut husks, sometimes using seawater, and lower-grade product can carry sodium and potassium salts that are hard on seedlings. Buying coir sold specifically for horticultural use, rather than generic animal or reptile bedding, avoids the problem. Reputable brands buffer and rinse it before sale.
The environmental argument, fairly stated
Peat bogs store large amounts of carbon and regenerate over millennia rather than years, which is the substance of the objection to harvesting them. That is a real concern, and it is why peat-free mixes have become mainstream rather than niche.
Coir is not cost-free either. It is a by-product rather than a purpose-grown crop, but it is shipped a long way and its processing uses water. Neither option is blameless, and the honest position is that this is a trade-off rather than a clear win for one side.
Choose peat if
- You are buying a commercial seed mix and it is peat-based. It will be limed and ready to use.
- You want the lowest price per volume, which peat usually is.
- You would rather not deal with expanding a compressed block.
Choose coir if
- The bog extraction argument matters to you, which is a legitimate reason on its own.
- You are mixing your own and would rather not adjust pH.
- You want a medium that rewets more easily after drying out.
- Storage is tight. A compressed block takes very little space until it is hydrated.
For ready-made mixes in both bases, see the best seed starting mix. For mixing your own, the DIY seed starting mix recipe.
The picks in full
Top pick
Espoma Organic Seed Starter Mix
Espoma
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A proper seed-starting medium: fine, light and deliberately low in nutrients, which is what germinating seeds need.
A seed carries its own food supply. That is why seed starting mix is low in nutrients on purpose -- the seedling does not need feeding until its first true leaves, and a rich mix at that stage encourages soft growth and fungal problems rather than roots.
Texture is the other half. A fine, uniform medium makes contact with small seeds all the way around, which is what triggers reliable germination. Chunky potting soil leaves air gaps and gives patchy results.
Plan the handover. Once true leaves appear, either start a weak liquid feed or pot on into something richer, or growth stalls.
What works
- Fine texture makes good contact with small seeds
- Low nutrients, which is correct for germination
- Drains freely, reducing damping-off
- Widely available
What does not
- Seedlings need feeding or potting on within weeks
- Small bags for the volume trays consume
- Light enough to dry out fast
Skip it if: you are potting on. Seedlings past their first true leaves want a richer mix than this.
| Type | Seed starting mix |
|---|---|
| Texture | Fine, uniform, low density |
| Nutrients | Deliberately low |
| Bag size | Commonly 8 and 16 qt |
The least fuss possible
Jiffy Peat Pellet Seed Starter Greenhouse
Jiffy
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Add water and sow -- no mixing, no mess, and the whole pellet plants out without disturbing the roots.
Pellets trade a little control for a lot of convenience. They arrive compressed, expand when you water them, and you sow directly into the top. Nothing to mix, nothing to spill.
Root disturbance is the real advantage. Plants in the cucumber and squash family in particular resent being pricked out, and planting the whole pellet avoids it entirely.
Two practical notes: open or peel the netting at planting time so roots are not restricted, and be aware the medium is peat, which is why coir-based alternatives exist.
What works
- No potting mix to buy, measure or spill
- Whole pellet plants out, so roots are never disturbed
- Dome and tray included
- Very cheap per seedling
What does not
- Peat-based, which is a real environmental objection
- Pellet netting can restrict roots if not opened
- Small volume means quick potting on
Skip it if: you would rather avoid peat. The pellets are peat-based, and coir alternatives exist.
| Type | Pellet seed starter with dome |
|---|---|
| Cells | Commonly 25 to 72 pellets |
| Medium | Compressed peat pellets in netting |
| Transplanting | Plant the whole pellet |
First-time seed starting
Burpee Self-Watering Seed Starting Kit
Burpee
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Everything in one box with a capillary mat underneath, which removes the single most common beginner failure: uneven watering.
Seeds fail for two reasons in a beginner's first tray: they dried out, or they were drowned. A capillary mat drawing water from a reservoir underneath removes both, because the medium takes what it needs and no more.
The dome is the other useful piece. It holds humidity during germination, which matters most for small seeds sown shallowly.
Take the dome off as soon as the first seedlings are up. Left on, it holds the still, damp air that damping-off fungus needs, and a tray can collapse overnight.
What works
- Capillary watering keeps moisture even without daily attention
- Humidity dome improves germination rates
- Nothing else to buy to get started
- Reusable for several seasons
What does not
- Cells are small, so seedlings need potting on quickly
- Kit price is high relative to buying components
- Dome must come off promptly once seeds germinate
Skip it if: you already have trays. Refill pellets and a dome cost a fraction of a new kit.
| Type | Self-watering seed starting kit |
|---|---|
| Cells | Sold in several counts, commonly 36 and 72 |
| Watering | Capillary mat and reservoir |
| Included | Tray, cells, dome, growing medium |
Common questions
Is coco coir better than peat for seed starting?
For germination they perform very similarly. Coir is close to neutral in pH and rewets more easily; peat is acidic and is limed in commercial mixes. The main argument for coir is avoiding peat bog extraction, which is a values decision rather than a performance one.
Does coco coir need to be washed before use?
Horticultural-grade coir from a reputable brand is already buffered and rinsed. Lower-grade product, particularly generic animal bedding coir, can carry sodium and potassium salts that are hard on seedlings, so buy coir sold for growing rather than the cheapest block available.
Why will my seed starting mix not absorb water?
Both peat and coir repel water when completely dry. Wet the medium in a tub or bucket until it holds together like a wrung-out sponge before filling cells, and give it time to take the water up. Watering a dry tray from above leaves dry pockets and washes seeds out of place.
Do I need to add fertilizer to peat or coir?
Not for germination. Both are essentially nutrient-free, which is correct, because a seed feeds itself until its first true leaves. After that the seedling needs either a weak liquid feed or potting on into a richer mix, whichever base you chose.
Sources
Factual claims on this page are backed by the published sources below, and product specifications are the manufacturers’ own. Where a figure is not published, we say so rather than estimating it.