An Assessment of the Suitability of Backyard Produced Compost as a Potting Soil

Compost Science & Utilization, (2009), Vol. 17, No. 2, 74-84

P.D. Alexander

Royal Horticultural Society’s Garden, Wisley, Woking, Surrey, United Kingdom

e-mail: paulalexander@rhs.org.uk

Current scientific knowledge of compost is largely derived from research into commercially produced green compost. This has shown that such compost tends to have high pH, high conductivity, and potential for organic and/or mineral pollutants and therefore can be problematic for use in growing media at high inclusion rates. Little work has been undertaken at an amateur composting scale and it is unclear whether these problems are prevalent in amateur-produced compost. This paper describes trials assessing the suitability as growing media of different composts produced using a range of amateur gardener methods. The resultant compost was then used to produce potting soil mixes with different compost inclusion ratios (with loam acting as the diluent) and assessed by growing tomatoes and lettuce. When comparing the effects of the compost mixes, the open vessels exhibited significantly higher weed germination counts than the wooden and plastic vessels. Turning the compost also significantly increased the weed count. In terms of seeds (lettuce and tomato), significantly lower germination counts were determined in the undiluted mixes when compared to the diluted mixes earlier in the assessment period. By the end of the assessment period these differences were reduced. By the final harvest, tomato heights and biomass were significantly greater in the undiluted mixes when compared to the diluted mixes and were comparable to the control mixes. Backyard produced compost would appear to have some value as a potting soil but the method of production needs to be taken into account when considering its use.

Copyright 2007, The JG Press, Inc.