Deep Mulch Garden Details

Garden LayoutIn permaculture we try to observe the interaction between elements of a system and then place the elements in relation to each other in a way that will enhance the productivity of the system.

Garden Layout - Key Hole Beds

In a traditional garden layout (and the suggested spacing on most seed packages) there are long rows of a single crop with enough space between rows for a person to walk down the row with a hoe.  Most gardeners can reach about 4 feet so if we use a 4' wide bed we can increase the number of plants by taking out the pathways between rows within that 4 foot bed.  You have all seen layouts with 4 foot wide raised beds separated by 2 foot wide path ways.  In that design, we have dedicated 1/3 of the garden space to pathways.  If we take those 4 foot wide beds and bend them into a circle leaving a 1 foot wide path way into the center and a 2 foot circle in the center to turn around, then we have a 10 foot diameter bed and have maximized growing space relative to pathway.

Selecting Materials

For deep mulch gardening we draw from the techniques of sheet mulching and hugelkultures.  Potential materials for a deep mulch include leaves, straw, hay, saw dust, wood shavings, wood chips and sticks, branches, and logs (Hugelkultur).  In the past we were concerned with the balance of nitrogen and carbon and the possibility that all the nitrogen will be tied up in the decomposition process but our experience shows that is not a problem with deep mulches.  We do not have peer reviewed research on sheet mulching, but we do have research on composting.

A compost pile wants to be 30 carbon to 1 nitrogen, well areated and moist, to heat up properly and rapidly decompose.  Fresh cut hay starts out at 30:1.  In 2010, at the Digital Garden on Leetsdale, Leo built his beds with wood chips.  A wood chip is around 500:1.  However, Leo's beds performed as well as the beds we built with hay, with no additional manure.  Subsequent research revealed that a problem in rapid decomposition in composting is the "bio availability" of the carbon.  In other words, we cannot count the carbon "inside" the wood chip in our calculations.  That is bad for composting but good for a soil ecosystem producing a continuous flow of nutrients.  It also explains the long term fertility described in the Hugelkultur literature.  The advantage to wood chips and branches is that they can be obtained free or produced on site.  A healthy soil ecosystem can eat 12 inches of hay a year and therefore that much hay has to be added each year.  Our wood chip sheet mulches last about four years and our five year old mulches built with branches show no signs of running down.

Sheet Mulch DiagramHOW MUCH MATERIAL

If we are building according to Toby Hemenway's formula in Gaia's Garden, here are the materials we will need:

One cubic yard is 3'X3'X3'. The foot print is 3'X3' and if we want to spread it 3” deep, as we do with the manure, we have 12 layers (36”/3”=12 layers). That means we can do 12 of the 3'X3' foot prints and cover 108 square feet (3'X3'X12 = 108 square feet) or approximately one key hole bed (10'x10' = 100 square feet). The formula calls for 1/2” to 1” on the bottom two layers. If we want to skimp, or if we are short of manure, we could stretch it to 162 square feet or about 1 and ½ key hole beds per yard.

Hay is harder to calculate because it comes in bales that are more compressed than we want. The best I can tell you is that we use about 1/3rd of a 3'X3'X8' bale per 100 square foot key hole bed.

If you are using wood chips, they come by the cubic yard. In that case, where we want to make the mulch 12” deep, we have three layers in each foot print, so each yard will cover 27 square feet 12” deep. That means, we will need about 3.7 cubic yards to cover each key hole bed that deep.

DRIP LINE CALCULATIONS

Drip Line ComponentsLaying out drip line requires a calculation of how much water we can deliver over a given area.  The variables are 1) the volume of water available at the source of supply, 2) the size of the hose through which the water will be delivered, and 3) the amount of water coming out of the emitters installed on the hose.  The variable that allows the least amount of water in the calculation determines the area that can be watered in one 'zone'.  Then we can plan multiple zones to run at different times.

For example, when we were preparing to build a garden at the Crescent Grange, we went to the water source which is a spigot on the outside of the building.  We opened the spigot wide to fill a five gallon bucket.  It took a full minute to deliver 5 gallons which means that the maximum amount of water that we can deliver to one zone is 300 gallons per hour.  (5 gallons x 60 minutes).

We will design for a 3/4 inch supply line that can easily deliver 300 gallons per hour (a 1/2 line will max out at 220 gallons per hour) so our limiting factor will be the length of drip line that we can run without exceeding the 300 gallon per hour available supply.  In this case, we are using .6 gallon per hour emitters spaced at 12" along the line so we can have up to 500 feet of drip line in a zone.  (300/.6)  Spacing our 1/4" lines approximately 18" apart over a typical key hole bed requires  approximately 43' of drip line per bed - or 43 emitters per bed delivering .6 gallons per hour each or 25.8 gallons per hour per bed.  300 gallons per hour divided by 24 gallons per hour per bed gives us 11.6 beds - which we will round down to 11 beds maximum receiveing water at any one time.

Generally, I run my drip systems 30 minutes over night.  Then, when we have high temperatures and low humidity, I give the garden another 30 minutes during the day.  That seems to be "plenty of water" most of the time.  Some more detailed observation might allow a gardener to reduce that amount.

Drip Line Options

Planting TechniquesWe can select a 1/2" drip line with preinstalled emitters on 12" centers (agrifim).  It is designed for long runs (up to 200') and few connections (a connection at each end of the run).  Another option is 1/4" line with preinstalled emitters on 12" centers (6" centers seems too close to me).  1/4" line has a maximum run of 30' and you still need a connection at the end of each run.  If you are doing a limited area that is not too big a problem . . . the connectors punch through the 3/4" supply line and insert into the 1/4" line with emitters.  3 "U" shaped loops will be sufficient for a typical bed and will be about 43' of drip line with six connections.  In 2011 the 1/4" line was going for $23.00 for a 100 foot roll.  We can also install individaul emitters where ever we want them.  In that design we run 3/4 inch drip line in a pattern and install emitters on 18" centers which allows us to plant row crops along the line.  Then we install additional emitters and attach 1/4" "spagetti" line out to where we want to plant larger plants.

Connecting timers and zone valves are beyond the scope of this garden layout page.

Building beds can be done any time of year but if you build them right before planting time then you will need to use some specialized planting techniques for planting in newly sheet mulched garden beds.

Building the Beds

Layout PathwaysWhen we began this work we were using hay.  Hay is expensive and 12" of hay will decompose in as little as one year in a healthy garden soil.  The hay must then be renewed every year.  For those reasons, we built up our mulch around the pathways.

We have since discovered, thanks to Leo Kacenjar at the Digital Garden on Leetsdale, that wood chips work just as well as hay in a sheet mulch.  (except a possible delay of a couple of months to get the decomposition going).  Wood chips can be obtained for free and take multiple years to decompose.  When we are building with wood chips we can just sheet mulch the whole area and then mark our pathways on top.  Don't put on the last 2" of seedless mulch in Hemenway's formula and use wood chips to mark the pathways on top of the last layer of manure.

Building a Hügel Mulch

 

Building a Hugel Mulch1. Start by soaking the area to be mulched with water.

2. Spread manure over the area about 1/2 to 1 inch thick.

3. Assemble a weed barrier by laying down a layer of cardboard with as little over lap as possible. Take newspaper and lay it out over the seams in the cardboard. Don't do a lot of unfolding. Just lay it out whole sections at a time. You will want to wet the paper as it is laid out if there is any wind at all. Lay out a second layer of cardboard and cover all those seams with newspaper.

4. Spread another layer of manure 1/2- to 1-inch thick.

5. Keep the water running and wet each layer as you go.

6. Cover the area with logs and then fill in the gaps between the logs with smaller branches and sticks.

7. Fill in any remaining gaps with wood chips.

8. Spread a third layer of manure about 1-inch thick.

9. Add 12 inches of wood chips on top.

10. Spread a final layer of manure about 1-inch thick.

11.You can now mark your pathways by laying out a line of wood chips about 2 feet wide and maybe 1 or 2 inches thick. 

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  • David Braden IV, Executive Director, Living Systems Institute
  • (303) 549-9787

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