How do I get good results from peat-free compost?
Peat-free is a technique change, not a downgrade — six habits built on peat that give poor results with wood fibre and bark, and what to do instead.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 5 min
- Safety
- caution
Short answer
Stop judging watering by the colour of the surface — lift the pot and judge by weight, and water slowly in two or three passes. Start liquid feeding at four to six weeks rather than eight to ten. Firm gently rather than pressing hard. Sieve it for seed sowing. Expect to water more often in heat, and buy fresh rather than using bags that have sat outside for a year.
Almost everyone who says peat-free compost does not work is using it exactly as they used peat, and peat-free does not behave like peat. It is coarser and more variable, it dries at the surface within hours while the core stays wet, it holds less water in total, its built-in feed runs out sooner, and some wood-fibre products draw down nitrogen as they break down. Every one of those has a straightforward response, and once the habits change the results are equal.
Safety
What you'll need
- Peat-free compost
- A liquid feed
- A sieve or riddle for seed sowing (optional)
- A tray or bucket for bottom-watering (optional)
Step by step
- Change how you decide whether to water — this is the big one.The top 20mm of a peat-free mix goes pale and crumbly within hours of watering, and it tells you nothing about the rootball. Lift the pot instead. Water one thoroughly, feel the weight, and compare. After a week you will judge it without thinking. A finger to the second knuckle, or a wooden skewer pushed to the base, does the same job.
- Water slowly, and go over it more than once.A single fast fill runs down the gap between the rootball and the pot wall and straight out of the drainage holes. Wet the surface, wait a minute for it to take, water again, and again. The second and third passes are the ones that reach the middle.
- Rescue a rootball that has gone water-repellent.If water runs out of the base within seconds, the compost is dry rather than wet. Stand the pot in a bucket or tray of water to about half its depth for twenty to thirty minutes until the surface darkens, then lift it out and let it drain.
- Start feeding sooner than you are used to.Bagged compost's built-in feed is designed to last four to six weeks in most peat-free products, and wood-fibre mixes can tie up nitrogen as they break down on top of that. Begin liquid feeding at around week four to six rather than waiting for the plant to look hungry.
- Firm gently, not hard.Peat-free mixes are coarser and the air spaces between the particles are doing useful work. Pressing hard, which is what peat needed to hold together, collapses that structure and produces a dense, airless block. Tap the pot on the bench and lightly settle the surface instead.
- Sieve it for seed sowing.Coarse chunks of bark and wood fibre in a seed tray mean poor seed-to-compost contact and seedlings pushing round lumps rather than through fine material. Riddle the top layer, or buy a proper peat-free seed compost, which is milled far finer.
- Expect to water more often in hot weather, not less.The larger pore spaces mean the total water held per litre of compost is lower. In a heatwave a peat-free pot will need water sooner than the peat one you remember, which catches people out and gets blamed on the product.
- Buy fresh and store it dry.Peat-free composts have a shorter useful life than peat. The organic components continue to break down in the bag, the structure collapses, and the nitrogen drawdown gets worse. A bag that has sat in the rain since last spring is a genuinely worse product. Buy for the season, store under cover, and use it up.
- Add loam for anything staying in a pot long term.Peat-free mixes collapse structurally within a season, like peat did. For shrubs, trees and perennials in containers, a third of loam-based John Innes gives weight and stability, or use a loam-based compost outright.
Tips
- Peat-free compost varies far more between brands than peat ever did, because the recipes are genuinely different — wood fibre, bark, coir, green compost and bracken in varying proportions. If one brand gives poor results, try another before concluding anything about the category.
- Coir-based mixes behave much more like peat in their water-holding than wood-fibre ones. If the watering change is the part you find hardest, look for a coir-led product.
- A 20mm mulch of fine bark or grit on the surface of a pot slows the surface drying that causes all the misjudged watering, and looks better too.
- Bottom watering — standing pots in a tray of water for twenty minutes — is the most reliable way to water peat-free seed trays and small pots, and it avoids disturbing the surface.
- In a greenhouse or on a windowsill, group pots together. It raises humidity locally and slows the surface drying that misleads you.
If it doesn't work
Surface looks bone dry, you water daily, and the plant is rotting
Cause: Reading the surface instead of the rootball — the core has been permanently wet — Fix: Stop watering and let the pot dry until it is noticeably lighter. From then on judge by weight. This is the most common peat-free failure by a distance.
Water runs straight through and out of the bottom within seconds
Cause: The compost has dried past the point where it will rewet from above — Fix: Stand the pot in water to half its depth for twenty to thirty minutes. Then mulch the surface to slow it happening again.
Plants pale and stalled at six to eight weeks
Cause: Built-in feed exhausted, possibly with nitrogen drawdown on top — Fix: Start weekly liquid feeding immediately. Next time begin at week four and mix controlled-release granules in at potting.
Poor, uneven germination in peat-free seed trays
Cause: Coarse material giving poor seed contact, plus surface drying between waterings — Fix: Sieve the top layer, cover seed with vermiculite, and bottom-water rather than watering from above.