12th Feb 2025
New research has shown that many bagged peat-free composts struggle to produce good results.
The research was conducted at the UK’s Stockbridge Technology Centre (STC), an independent agricultural and horticultural center of excellence.
The researchers bought bagged compost from a variety of sources, including online retailers, garden centers, and DIY stores.
To test the compost, they grew tomato and petunia plug plants and placed them in a greenhouse under supplementary lighting.
However, testing found that a significant number of composts didn’t support strong plant growth after four weeks.
After five weeks of growing, less than half of the bagged composts produced excellent or very good results with petunias, while 23% were rated as poor or very poor.
In contrast, all reduced peat composts gave performances which were either good, very good or excellent.
The results were similar with tomatoes—after three weeks, 17% of the composts produced poor or very poor results. By comparison, reduced-peat compost was rated either excellent (90%) or very good (10%).
There were a number of reasons for the poor performance including:
- Lack of nutrients
- Poor structure
- Contamination
The researchers found that adding NPK fertilizer before planting significantly improved results. They also tested applying liquid feed during growth, but this proved less effective than applying before planting.
The news is concerning for gardeners, as peat-based compost is increasingly restricted in the UK for environmental reasons.
Takeaway for gardeners
Peat harvesting is damaging to the environment, and it’s important that use is reduced or eliminated.
However, not all peat-free composts perform the same, and some gardeners are reporting disappointing results.
Gardeners who wish to get good results with peat-free compost should:
- Choose compost carefully – Look for well-reviewed brands and check ingredient labels for a balanced mix.
- Check plants regularly – Monitor growth for early signs of problems so you can take action quickly.
- Use liquid feed when plants struggle – If plants aren’t growing well, feeding can help, though it’s not always a perfect fix.
For further insights, see The Problem With Peat-Free Compost (And How to Fix It).