Peat free potting compost mix - as used at Sampford Shrubs since 1995.

This page is intended only as a guide for those who want to experiment with peat free compost mixes for their own use. We do not sell this compost and accept no liability for the use of this or similar mixes.

The source compost must have been thoroughly composted at a high temperature to kill all pathogens and weed seeds. A growing number of local authorities throughout the UK are now composting their own green waste - even if yours doesn't compost they should be able to tell you who does in your area. Our supply source is either Wyvern Waste in Taunton or (more recently) Westcountry Compost in Exeter. We changed because Westcountry is a more mature product - it arrives colder - and the pH is slightly lower possibly reflecting the more acidic nature of the rocks in west Devon.

Your local source should be able to give you a typical analysis. For experimentation you will probably be able to buy a few bags but when you get serious it's cheaper by the lorry load!

Like any new growing medium you will need to learn how to work with it. It is not like peat, bark and coir composts which are low in nutrients - to these composts you must add just about everything you need. The older the composted waste is, the better it is for growing plants. We get a lorry load of well composted material delivered over winter and use through the subsequent season. If it's still very hot and steaming as it arrives then the material is too young - you must leave it at least couple of months more to mature. Weed seeds have never been a problem with well composted commercial green waste -it is effectively sterile from this viewpoint. Some of the peat free ready made composts we have played around with in the past have not been good - far too much nitrogen tie-up from poorly composted ingredients appears to have been some of the problem.

Early on, we realised that some some subjects with which we had problems were now growing well in the new composts. Hebes, Fremontododendron and other plants which suffered from phyphtoptera root rots were now quite healthy and without drenching with fungicides (yes we did use these many years ago out of necessity). We then found that research results elsewhere (particularly at Exeter University) were also demonstrating this benefit. The original source of our information was:

The presence of beneficial fungi inhibit the ability of pathogenic fungi to proliferate and damage plants. Hedges, S. 1996. Compost is a natural-born killer. New Scientist 21 September: p25.

Two useful references:

Compost is a natural-born killer
Antagonism of fungi from composts to soilborne pathogens

The nutrient levels of composted green waste are quite high - hence the low levels of added nutrients which we use. A typical analysis might be:

As you can see, the natural pH of this compost is quite high - in fact it is towards the high end of the tolerable range for growing most ornamental subjects. You do not need to add any lime. Such composts are no good for ericaceous plants (for these we use coir/bark mixes) and it cannot be mixed successfully with ericaceous composts. I suspect this is because the compost has what is called a high buffering capacity - this means the pH is very stable and little affected by other factors. Our mix is now 16mm sieved. Material you buy in bags has probably been passed through a 16mm sieve or even finer.

Apart from using a waste material to good effect and avoiding the plunder of peat moors and the loss of wild habitats there are some major benefits in using green waste based composts:

Some drawbacks include:

Our basic compost mix:

* currently experimenting with substituting one third with bark chips

If your supplier has a Soil Association certification number and you can find a substitute for the slow release Osmacote which conveniently supplies all trace elements then you ought to be able to produce a compost mix which meets organic standards.

Rooting trial using various composts

In spring 2001 we carried out a simple trial using dahlia cuttings and 6 rooting compost mixes. All cuttings were dipped into a standard rooting powder before inserting individually in 7cm pots into the various composts. Rooting media from left to right are 1. our regular compost mix (as described above); 2. 50% coir, 50% compost mix; 3. 50% composted bark chips, 50% coir; 4. 100% coir; 5. 50% compost mix, 50% composted bark chips; 6. 100% composted bark chips. The results speak for themselves!

As a growing medium for hardy herbaceous plants and shrubs, the compost above produces excellent results for us. Soil borne diseases which are a regular problem with peat based composts are no longer an issue, the robustness and vigour of our plants is excellent and frequently remarked on by our customers. There are a few subjects which do not thrive and the higher conductivity may be an issue here, but for the huge majority, compost based around green waste is vastly superior to peat and we would never want to turn that particular clock back!

No peat used here! - photo taken 30 May 2004

More pictures of peat free plants

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