Sheet Composting - an energy saving way to enrich your soil

Not everyone has the room or enough materials for a large compost heap.  Micky,  our organic horticulture tutor, has converted what was her lawn into a productive fruit, vegetable and flower garden through the practice of sheet composting.

Sheet composting in situ is ideal when making a new plot or reviving and improving the soil in an existing plot.

For this method to work you need to accept the following:

1. Not use this garden bed for one or even two years for growing small seedlings or seeds as plants don't thrive when materials are being broken down into humus. However, you can spot plant potatoes or pumpkins as long as you plant them with some matured compost in the planting holes.  

2. You are happy to have an area covered with carpet or cardboard left for a long period. You can as suggested above plant pumpkins and the area by summer would be covered with greenery.

If planting trees, shrubs or herbs you can spot plant in a sheet composted area. Fill the planting space with some worm vermicast or mature compost and as these plants mature they will feed on the compost created under the sheet.   

After viewing Micky's slideshow of her place, I was keen to get some practical experience on sheet composting and got the opportunity on two occasions over the holidays.  

  

Two large raised gardens at the bottom of the stairs. The hedge  on the left was trimmed
and included in the sheet composting for the closest bed.

First at my friend Julia's new house in Tauranga. She has inherited two lovely raised bed gardens but the soil was rather tired with no sign of a worm. 

I suggested she plant up one of the beds for summer vegetables and use the other to recycle materials through sheet composting.  Luckily I  happened to have some EM (Effective Microbes) and molasses with me.

EM does not like chemicals so if using town supply water you need to sit a bucket
for a day to get rid of the chlorine.  Ideally you should use rainwater rather than tap water.

 If Julia didn't know me so well, she may have felt when I was mixing up my brews that this was a little like witchcraft.  I first mixed 20ml of molasses with some hot water to melt the molasses.  Then add more cold water to 1/3 of the bucket before adding 20 ml of EM to the cooled water. Stir and leave in a cool shady spot to activate.  After a few hours add the remaining water to make up 10 litres.  I usually make up a 20 litre bucket at a time but at Julia's we only had a 10 litre bucket available. You can simply dilute the EM but adding the molasses gives the microbes a head start - just like feeding yeast with sugar. The microbes begin to multiply and are ready to get to work breaking down organic matter, your waste materials.

These are the instructions on the EM Garden 1 bottle.

You do need EM for sheet composting to work effectively because the materials are covered with no air flow and could become anaerobic without the help of the Effective Microbes that can survive in anaerobic conditions.  EM activates the breakdown of materials into compost. You can get EM online. I got the EM1 Garden and molasses but you can use food grade molasses as well.  Check out  www.emnz.com to find out more about EM and all the good things you can do around your garden and home.

The soil was forked to encourage aeration before adding the first green layer.

Back to the sheet composting. First of all I aerated the soil in the raised bed with a fork.  You can do this on an existing garden bed. If making a new garden on a grassed lawn there is no need to dig over, just aerate with a fork.  The first layer should be a thick (10 cm) layer of fresh lawn clippings. Nothing kills grass like lawn clippings. That first layer should always be green (high nitrogen) materials.

This is the difference to a standard compost pile where you start with a carbon layer over top of a stick base to allow for air circulation.  The green layer at the bottom of the sheet composting serves to attract worms and other helpful creatures in the soil to work your waste materials into humus.

If you use lawn clippings make sure the lawn has not been sprayed with any broadleaf
herbicide.  This herbicide will kill microbes.

Julia didn't have any lawns or household scraps for that first high nitrogen layer so I used a good layer of cut up shrub and hedge clippings that had already been cut up and put into bags to be taken off the property.  This first layer because it has woody hedge clippings will have quite a good carbon ratio.

They live just up from the beach and there was plenty to seaweed available.  Seaweed will be an excellent feed for the soil.

Seaweed is an excellent green layer if its available to you.

 If you have access to manure that could be used instead or as well as seaweed.

Shredded paper was our carbon layer.

We didn't have any straw or hay available but there was a big bag of shredded paper so I topped off the sheet composting with this.  You can also just rip newspaper into strips. Newspaper is a good source of carbon but it disappears quickly and doesn't make much bulk.  Autumn leaves can also be a good carbon layer but don't layer too thickly or they will compact.

The EM activated solution I applied with a watering can rose. Another application device is simply an old bucket with some holes drilled in the bottom. I had to apply it onto the final layer because the city water had to sit for a day to get rid of the chlorine before mixing up molasses and EM.  But if you have the EM activated in time you should put it on after each green layer.

The ideal cover is one large piece of carpet. We used what we had on hand...cardboard from moving boxes and secured with paving stones.  Another disposal problem solved. The purpose is to cover fully so that no weed seeds will germinate in the light and to keep the heat contained to assist in the speedy breakdown of materials.

The two garden beds front one for summer planting and the back one under
sheet composting.

While the other raised bed didn't have great looking soil, it wasn't practicable to have both gardens out of action. So I gave it a feed of Biofert general garden fertiliser that has some trace elements and is coated in fish fertiliser and microbes to give this garden plot the best start.  Julia tells me everything is growing well.  Next growing season she will use the sheet composted bed. An option would be to do the second bed in two stages by sheet composting 50% of it once the other bed is back in use. Then the following season complete the other half.   Hopefully, the wait will be  rewarded with be soil full of worms and healthy microbe activity.

By creating her own compost Julia has saved herself from hauling in ready bought compost and will no longer need to get rid of her plant trimmings off her section. If using bagged compost all the living organisms would have been killed off anyway...as Micky says "all you are buying is expensive mulch material".  The compost produced under this cardboard cover will in 6-8 months be teeming with all kinds of  microbial life. With EM and sheet composting you are taking care of the soil first so that the plants will look after themselves.

Using EM ensures the soil is innoculated with good microbes right from the start and that will help plant health by making available to the plants minerals and trace elements present in the soil and keeping in balance any bad bacteria or fungi.

Julia's lovely sub-tropical woodland garden.

Julia has a garden with some lovely plantings and there will be plenty of fallen leaves, hedge clippings and weeds for her to re-use as organic matter to feed the garden.  I just have to convince her to enlist the help of EM to speed up the process.

By the way EM is the active ingredient in the Bokashi bran used in the composting system for kitchen waste. The run off from Bokashi composting can be diluted to introduce these microbes to the soil but it will be more diluted than using EM preparations.

In the New Year we travelled south to our wild garden at Broad Bay on the Otago Peninsula where we retired two areas into sheet compost beds. These beds were made higher than Julia's because we had available more green and compost materials.

This is the first sheet composted area measuring approximately 2 square metres.  It doesn't look very sightly..I know, but it is hidden from view of the house by planting around it.

You can see the white string like roots of couch grass.

Half of this area had previously a good depth of wood chip mulch with the white stringy evidence of fungi (and even some mushrooms) breaking it down into humus but underneath this is heavy clay.

Our tenants asked whether the mushrooms were edible. Mushrooms are something I know
very little about but I said no unless they could find someone who could identify them as edible.

And  it is full of couch roots (aka twitch in the North Island) so I couldn't simply fork it to aerate before adding the first layer. I had to take out as much couch grass as I could because you can't smother couch grass.  The mulch of course brought the couch to the surface which makes it easier to pull out of the friable mulch rather than in the dense clay.

The lifting of couch grass enabled me to aerate the soil before the first layer.

 The other half of this area was so wet I could hear that sucking sound of water.  The rest of the garden was very dry as it is all over the country this summer. The clay in this area that had trapped the water.   I am hoping sheet composting will encourage worms to aerate this heavy clay.

The smelly first layer of half decomposed kitchen waste.

The first layer was a pretty smelly layer as it came from our tenants household kitchen waste that was  housed in a black plastic compost bin. The bin wasn't working because they were not adding enough carbon materials and too much sloppy nitrogen rich wastes.  The day before  I had watered it with EM and left the sheet composting to our final day when we would have all the other layers gathered from our weeding and collection so that the funky smell would quickly be covered and not offend the noses of our tenants and neighbours for long.

This half decomposed anaerobic mess made a layer of around 10cm high and I followed up with a watering of EM solution to help to decompose this material.

Straw is the best carbon layer because it doesn't have weed seeds attached. But dried weeds
are also a carbon layer.

Next came a layer of dried out weed materials.  It was too early to be able to purchase any straw or hay but luckily the weather was so dry and hot over the 4 days of weeding that the weeds dried out and could be used as our carbon layer. Keeping it covered would avoid the usual problem of weed seed germination.

Peter collecting seaweed at what is locally called "Smelly Point"

Like Julia we live beside a wonderful garden resource, seaweed.  Each low tide Peter collected buckets of seaweed for use in the sheet composting and as mulch around the garden where we had weeded. Seaweed was the next layer and luckily my sister Kerry who keeps hens gave me a bucket of her hen manure that was mixed with the wood shaving bedding she uses.

The next layer took me time and a lot of hand cutting to process.  (Oh for a mulcher!).  It was a massive pile of shrub leaf and woody trimmings.  The sticks that were too thick I put into a pile for a later stick base for a free standing compost pile.  The mix of nitrogen and carbon makes these shrub or hedge trimmings an excellent layer for the sheet composting. Plus I saved the energy and cost of taking these materials off the property to a refuse centre.

On each green layer I watered in EM.

On top of the shrub cuttings I put some compost and a heap of comfrey and borage leaves and a final watering with EM.   I also watered each layer after the first mucky layer with water as you would a compost heap. The final layer was a thick covering of the lovely oat husks from Harraways oats factory.

The end heap was about 30cm high.   I covered it with carpet and weighed it down with pieces of wood so that the wind wouldn't blow away the cover.

This photo was taken at the end of October. By January the growth was up to the
top of the concrete fence at the back.

Previously we had been retiring areas of the garden with just laying carpet to keep the weeds down. We have decided to uplift the carpet areas and create sheet composting so that the soil underneath will be conditioned as well as keeping down weeds. It's hard to believe but this wild borage, comfrey and broad bean garden has carpet covering most of the area behind the wire grid.  All these plants grew around the perimeter of the carpet covering the whole area.

I didn't have time to track down carpet but local a carpet company
had a sign outside their shop offering free carpet sample squares.
These need securing down with objects to keep in place but will work better than cardboard.

I added carpet squares over the heap which will have more durability than the cardboard boxes.

It doesn't look as nice as bare ground but I decided like Micky to look after the soil rather than look after others aesthetics of how a garden should look.  I also know that the borage and comfrey will bloom again and present us with an attractive border of colour next spring covering the sheet compost area as it did last year.

I was working to a deadline so hastily made a compost heap using all the same layers. As a heap the greater mass means it will heat up fast and breakdown faster than the sheet composting areas. We would have lifted another carpeted area to create more sheet composting but time restraint meant a heap would be the easiest way of processing all the remaining weed, seaweed  and other available materials.

The heap was covered with a thick layer of oat husks. These are
a great local mulching material that is light, easy and nice to handle
with an intoxicating sweet fermented smell.

When I returned 4 days later I was very pleased to see signs of active fungi (white). The "ouch test" when I put my hand into the central chimney told me there was good heat in the heap.

Left: the heap after completion; Right the heap four days later with
carpet square covering.

 I covered the heap with newly acquired carpet squares to replace the original impervious teal vinyl so that rain can slowly soak into the heap without drowning it.  This heap was done in such a hurry I know the materials are not as broken up as they should be to activate a rapid break down but I was happy we had managed to deal with all our weed materials and not have to cart them to a refuse station.

The bad guys including couch grass, convolvulus and buttercup were stuffed into large green rubbish bags and put under the trees to slowly break down. Even these bad guys need air, light and moisture to survive so in 2 years time the material will be able to be put through a compost heap without any fear of reinfecting the property.

When I return in April this year I will check on the progress of the sheet composting break down of the organic matter under the carpet covers.

Sheet composting may be a waiting game but it's also a way in which to enrich your soil and save  labour and energy compared to buying in compost or making your own separate heap and then digging in that compost.

Postscript: A handy hint for deterring Kikuyu grass

Our tutor Micky while illustrating the importance of keeping records of your gardening observations. She told us of her discovery regarding Plane and Oak tree leaves and their chemical properties that deter Kikuyu grass from entering a sheet composting pile.  This could also be used for mulching along the edges of your garden where Kikuyu grass tries to enter. Micky only discovered this because she usually used these leaves in her sheet composting areas but one year she didn't.  The gardens that have been sheet composted with a layer of these particular leaves she could see where Kikuyu grass did an about turn away from the plot.  The gardens without these leaves has got Kikuyu growing into them.  While the chemicals in the Plane and Oak leaves deter grass growth they didn't affect other plants or the microbe activity in the soil.  So I will be hunting down some leaves from our leafy Auckland suburbs this autumn.