Compost Trials - Results

Compost trials â?? November 2010
(some photos at foot of this post)

Having read several accounts regarding the qualities of various types of compost I decided to carry out my own trials on the composts I use.
My hypothesis is that home produced composts can be as beneficial or better for seedling growth as bought compost and are economically advantageous to the grower.

The composts were â??

Worm bin compost.
This is produced in two worm bins ,â??Daleksâ? ,fed mainly by kitchen waste , card, kitchen towel, occasional grass cuttings and lawn rakings and occasional layers of leaves and wood shreddings and some vegetable material from the vegetable plots. The input-output cycle takes 6 to 8 months.

Garden compost
This comes from our â??big heapâ? which runs on a two year input â?? output cycle and is started every autumn with a layer of lawn rakings of moss and grass, fallen fruit, shredded leaves and as the year progresses has layers of grass cuttings, and vegetables added along with layers of leaves and shredded woody material. At the end of each 12 month period it is turned over into another heap and has potatoes are planted in it. This second year compost is then bagged in autumn ready for use in spring.

Seed and Potting compost
This was J Arthur Bowers compost which I use from time to time. This compost has added nutrients. The small 15 litre bag cost £2.49 at our local garden centre.

Observations on the physical structure of the composts -

Worm bin compost
Iâ??ve noted when using this that it tends to be quite wet and sticky when first removed from the bins. It also seems to hold moisture for several weeks when spread on the garden. The general structure is finer than the garden compost.

Garden compost
After the two year cycle this is quite fine in structure, though less so than the worm compost. It also contains very small particles of woody material that have not fully decomposed.

JAB - Seed and Potting compost
Finer and more uniform in structure than the other two composts and with sand particles visible. It contains added nutrients.

Preparation â??

The two home produced composts were first dried for 5 days to kill off any wild life by spreading out in seed trays in a large heated propagator and then passed through a sieve to break up any lumps and to remove large particles.
Three 450 ml seed trays were filled with the composts and lightly tamped down to just below the rims of the trays. The trays were then placed in a larger water filled tray until they reached saturation when they were removed and allowed to drain.
It was noticeable that the worm and JAB composts settled slightly in the trays following saturation while the garden compost rose significantly. This latter phenomenon is probably due to the small residual particles of woody material in the garden compost expanding when rehydrated. Although shredded woody material is also added to the worm bins, worms aided by other insects to reduce the material during the digestive process.
After the water saturated trays had drained I weighed them as I wanted to monitor relative water loss during the trial. The garden compost had absorbed significantly more water than the other two composts.

Seed sowing â??

Each tray was sown with 2.5 ml measured volume of curled cress seed which was then sprinkled with a thin layer of perlite. The trays were then placed in a small electrically heated propagator close to a south facing window.

Results â??
Growth
All trays had germinated by day two and growth in height was pretty much even throughout the trial period. Germination was less successful in the garden compost while the JAB and worm composts were more or less equal.
Vigour (as opposed to height) was noticeably less in the garden compost and towards the end of the trial period the seedlings in the garden compost were looking quite floppy and more spindly than in the other two.
Colour was the same in the JAB and garden compost trays while the worm compost produced a very slightly darker green leaf.

Water Retention/Loss
When the composts were saturated at the start of the trial the garden compost absorbed approximately 30 ml more of water than the other two and as mentioned above it expanded while the other two compressed slightly. This â??extraâ?? water was lost by day 3 but throughout the trial the garden compost retained more water than either of the other two and significantly more after day 7.
Note that the graph rises at three points â?? this is due to 30ml of water being added to each tray to maintain growth.

Conclusions
Worm compost and JAB are much better media than plain garden compost for growing cress. Though this is hardly surprising given that JAB has nutrients added and it is known that worm compost is significantly higher in nutrients than ordinary garden compost.
In this trial the worm compost produced cress that was slightly greener than that grown in JAB and garden compost possibly indicating healthier seedlings.
Next steps
This experiment involved growing seedlings over a fairly short period. I intend to try a similar experiment with broad beans and radishes in larger pots and over a longer period.

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First class Dave. Its nice to see some well executed science in action. I think its so easy for all of us to give opinions when we don't neccessarily have the facts to hand. :gnthb:

 

Blimey Dave, thats a lot of effort you've gone to there, well done Sargent.

Have you copied this thread to the compost section too ?

 

Why are my ears burning? :hehe:

 

That's really interesting and useful, Dave. I use garden compost mixed with a bit of Levingtons to give it a bit of oomph. It works for me for just about everything!

 

Kristen - I could see my reflection in the computer screen when I wrote that - I couldn't see anybody else. :hehe:

 

brilliant Dave, am about to start my own trial on peat free growing medias for university would you like me to do some pH tests for you? only small samples would be needed

 

Would be interesting to compare all/most/most of the other composts. But thanks Dave, though I have to say if you why not make your own, otherwise it's only going to go to waste anyways.