Category Archives: Fertilizers

Sheet Mulching Re-visited

Last week’s blog included a link back to our October 2016 blog on experimenting with sheet mulching (also known by some as “lasagne gardening”) http://wp.me/p5JEJY-YZ so I thought we ought to re-visit and see how that worked. Sheet mulching is the layering of different kinds of compostable garden waste (sometimes with old newspapers or cardboard as well) on the surface of poor garden soil. The aim is to quickly add organic matter to the existing soil, improving drainage, water retention and fertility.

OLYMPUS DIGITAL CAMERA

I had several questions in my mind last fall when this experiment was carried out:

1. Will the cardboard decompose?
2. Is the “green” and “brown” balance right?
3. Will the raccoons and skunks churn it all up?
4. Will there be a crop of new weeds from the imported materials?
5. Will the cold Colorado winter simply stop any decomposition from taking place?
6. Will there just be a smelly slimy heap to remove next spring?
7. OR, will we have achieved that elixir of gardening – fertile, well-drained, moisture-retentive soil???

The experiment has been going on for some eight months now and these are the answers, so far:

1. YES. Some digging about at the base of the layers revealed no sign of cardboard except for a few stray bits of plastic tape that didn’t get removed when I broke down the cardboard boxes.
2. Probably YES. Though close inspection revealed that in some parts the grass clippings were laid too thick and would have done better if they’d been mixed in more with the dried leaves.
3. NO. Apart from a few little exploratory digs by some critters, the layers remained intact.
4. NO. Initially there was some germination from seeds (unidentified grass/cereal) which were in the chicken coop material I used, but these were easily pulled in the first couple of weeks. Since then not a single weed has appeared.
5. NO. Digging into the layers revealed pretty well composted good, brown material though not everywhere. Lots of worms too. Straw seems to have been the hardest to break down and is still recognizable in some places.
6. NO. See 5.
7. Well, MAYBE ….

IMG_1049

The native grey clay soil is still there beneath the sheet mulch

IMG_1047

Well on the way to being compost

There is no doubt that we now have deep layers of composted garden waste on our borders. The layers have not been totally absorbed into the soil below. They have shrunk in depth by a couple of inches which is probably mainly due to gravity and the reduction of air pockets. I accept that these borders may remain as “raised” borders for some time.

So, what happens next? I expect these sheet mulched borders to continue to decompose over the summer and, perhaps, by next spring will no longer be “raised”.

But I can’t wait until then to get new plants in.  Already, I have a planted a Japanese maple and some hellebores in one of the beds (both should benefit from the rich compost.  I dug holes in the compost layers, put in some native soil from elsewhere in the garden and planted and watered.

I was concerned that the compost itself would not hold the plant roots securely which is why I mixed in garden soil from elsewhere to give weight. It will also provide mineral nutrients that may not be present in the compost/mulch. Now, some six weeks later, the new plants are all well rooted and looking good.

IMG_1227

Japanese maple and hellebores just planted

So, is it worth doing? I’m giving the experiment a qualified “yes” at this stage.

I think it works for areas that have been neglected or are being cultivated for the first time. There is an initial effort in gathering the materials and building the sheet mulch layers, but then you just sit back and wait.

Does one big “hit” of compostable material work better than cumulative additions over the years? I don’t know. Time will tell as I compare these borders with others in the garden. Certainly, I got a lot more compost onto the borders than I could generate annually from my compost bins. (You don’t get a lot of kitchen waste from two people; and a modest-sized, young garden doesn’t produce much waste either.)

It might have been less work to simply go out and buy bags of compost from the garden center or big box store. That would have been expensive (my materials were all free). There are no regulations on what goes into bagged compost for retail sales.  At least I knew exactly what was in mine.

Aside from these thoughts, there has definitely been a great sense of satisfaction in doing the experiment.  It was interesting.  It was good exercise.  It was free.  I turned what other people thought was just rubbish messing up their yards into useful, re-vitalizing material for our garden and plants.

Anne Hughes/A Denver County Master Gardener

Advertisements

Sheet composting or … cooking up an experiment in the garden

I’ve always known that the soil in the garden was the key to planting success.  So, when we started our new Denver garden in 2014 we turned in most of the turf and dug, weeded and added leaf mold to the topsoil.  (We had kept all the fall leaves for this purpose.)  Then all the bare soil was covered with a 3-4 inch mulch of wood chips.  Key trees were planted in spring 2014 with more trees, shrubs , ornamental grasses and herbaceous perennials following in 2015.  We watered diligently till the winter and snow came.  We thought we’d made a good start.

In spring 2016 I was delighted to see our young trees and shrubs budding out .  Most of the herbaceous perennials had survived, but they didn’t increase in size during the summer. They hardly bloomed.  They didn’t die.  They just sat there.  Watering seemed to make no difference.

I figured that the larger plants (trees and shrubs) were able to get their roots down into the clay where there was more moisture and more nutrients.  But the perennials were struggling with their smaller root balls being mostly in the 8-10 inches of sandy loam topsoil.  Here water drained away quickly and despite the wood chip mulch, the unrelenting sun and high temperatures baked the soil to an iron hard cap over dull powdery stuff below (if you could get the spade in that far!).

I had a soil test done by the soil laboratory at CSU which told me that our topsoil was low in nitrogen and organic matter.  Ah-ha!  That is why the plants weren’t thriving.  The lack of nitrogen was slowing the development of stems and leaves.  The lack of organic matter meant the soil wasn’t holding sufficient water for the plants’ roots to take up.

OK, I thought, we have to do more to improve the soil. I’ve never liked the idea of just throwing chemical fertilizers at the garden.  It’s expensive, wasteful and potentially dangerous to the wider environment.  Double-digging and adding store-bought amendments (of uncertain quality) is back-breaking and expensive. What to do?

Soil is not tilled in the natural world.  Fertility is built up by the decomposition of leaves, twigs and other plant waste on the surface.  Soil texture and nutrient levels are also improved by the actions and decomposition of organisms living in the soil and plant roots.  I’d just been reading about permaculture gardening techniques and the soil improvement technique of “sheet composting” or “lasagna gardening” seemed to be what we needed.

This is a way of building up organic matter and nitrogen in the soil without digging.  You gather different sorts of compostable material (green garden waste, compost, grass clippings, straw, dried leaves, well-rotted manure are just some you can use) and pile them up on the soil in layers.  Hence “sheet” composting or “lasagna” gardening. Essentially, you are making compost directly on top of the soil rather than in a compost bin elsewhere and then transferring it later to the garden.

Many books suggest that you also lay newspapers or plain cardboard down first to smother any existing weeds in the ground.  This is usually where you are trying to improve a weedy, uncultivated area.  But such two dimensional materials can be a barrier to the passage of water, nutrients and the essential soil creatures (see below) that you need to make the process work.

Cardboard layer to start

Cardboard layer to start. Existing wood chips raked on to path first.

Cardboard often incorporates waxes which inhibit the movement of moisture and make it hard to break down.  Shredded newspaper in half inch layers may be a better alternative, but not perfect.  I did use cardboard, but in hindsight probably didn’t need it as the soil was not weedy at all.

Every layer has to be thoroughly soaked with water including the existing soil.  The fungi, bacteria, insects, beetles, earthworms etc. that will break down your materials need water to do their work.

My “recipe” comprised from bottom (soil level) to top:

  • cardboard (on reflection, probably not needed)
  • garden compost (precious stuff from my own bins)
  • grass clippings from a neighbor’s “pile” and half a bag of left-over peat moss
  • partially decomposed garden waste from another neighbor’s “pile”
  • wood shavings and straw from another neighbor’s old chicken shed
  • grass clippings again
  • leaves collected in our leaf cage from the previous fall
  • more partially decomposed garden waste
  • wood chips to hold it all in place and for aesthetic appeal

The layers amounted up to about 12 inches of material.  Each layer was watered in.  Grass clippings were laid in approximately 1 inch layers while the other materials were laid in 3-4 inch layers.  You need much more brown material by volume than green.

Straw and partially decomposed garden waste

Straw and partially decomposed garden waste

Just like making compost conventionally it is important to have a mix of “green” and “brown” materials or, in chemical terms, sources of nitrogen and carbon.  Too much green (e.g. grass clippings) and you have too much nitrogen.  Too much nitrogen will encourage leafy top growth in your plants at the expense of root and fruit/flower development leading to straggly unhealthy plants.  Too much brown and the materials won’t break down sufficiently.

But the green/brown or nitrogen/carbon balance isn’t just about your plants.  All the living creatures in your soil need the right balance too.  They have to live, multiply, work the soil, die and decompose in order to release the precious nutrients to your plants.  The soil creatures need to feed before your plants can.

OLYMPUS DIGITAL CAMERA

Last year’s leaves go on

It’s important that the materials you bring in don’t also bring in weed seeds resulting in a huge weeding problem for the next year.  But the theory is that any weed seeds that do come in will rot in the damp condition of the layers. And if they don’t rot first, they won’t germinate anyway due to lack of light.

The biggest part of this job is sourcing and gathering all the materials.  There were many trips to neighbors’ gardens with rakes and shovels.  Then the trips home again with a car full of other people’s “waste” in old plastic bags. It is hard work.

OLYMPUS DIGITAL CAMERA

The finished thing

So, now we have some 60 feet of garden borders resting for the winter under their layers of composting (we hope!) materials.  We also have many other areas where fewer layers were used (mainly straw with grass clippings or partially decomposed garden waste) to about 3-4 inches to perk up the soil around and between trees and shrubs.

Many questions remain:

  • Will the cardboard decompose?
  • Is the “green” and “brown” balance right?
  • Will the raccoons and skunks churn it all up?
  • Will there be a crop of new weeds from the imported materials?
  • Will the cold Colorado winter simply stop any decomposition from taking place?
  • Will there just be a smelly slimy heap to remove next spring?
  • OR, will we have achieved that elixir of gardening – fertile, well-drained, moisture-retentive soil???

Well, the answers to all these questions will be given next year when I report back in another post.

In the meantime, what do you think? Have you tried this? Did it work well? Please share your comments below.

Anne Hughes  – Denver County Apprentice Master Gardener