Wednesday, 14 December 2011

Mulching experiment

Green manure: Hungarian rye on the left, tares to the right. Will be dug in early Spring.

It's been the mulching time of year, well, more in Autumn, I'm just writing this up late! I decided to try experimenting with a couple of different mulching techniques on a couple of beds at the lottie which didn't have green manure in them, so they would not be bare over winter. The main reasons for mulching are:
  1. Killing weeds by denying them light
  2. To conserve water - reducing evaporation
  3. To protect the soil from erosion or capping
  4. To encourage biological activity
  5. To add organic matter and nutrients to the soil
(from The Earth Care Manual, p.194)

The first bed I am doing my mulching experiment on had potatoes growing in it this year, and will be planted with courgettes, pumpkins & squashes and corn in 2012. My key aim for the mulching on this bed was to add organic matter and nutrients in preparation for plants that will need lots of food. A secondary aim was to kill weeds (annuals) by denying them light.

Having already tried to clear the bed of perennial weeds like couch grass when it was first dug, and again after I pulled up all the potatoes, I had hoped that I had got it all. Couch grass is very sneaky and the tiniest amount left behind will start a new plant. Clearly I haven't quite mastered the art of getting rid of perennial weeds as I still have couch grass appearing! So I therefore first did my best to dig out any perennial weeds, again.

Experiment 1: standard cardboard & compost mulch

I then covered the bed with cardboard, and then added in a couple inches of compost on top of the cardboard. The cardboard should help kill off any annual weeds. It will breakdown over winter, and the worms will take the compost down into the soil, doing the handy work of adding it's nutrients to the soil.

This is a fairly standard type of mulching, so I'm not doing anything new. I'm going to monitor this bed over winter and see how it breaks down. I will probably add another layer of mulch in early spring, as pumpkins etc are hungry feeders and I want to give them the best possible chance of yielding lots of yummy food.

The experiment part really comes in with comparing this standard way of mulching with another bed I mulched. This bed had broad beans on it this year, and I will be planting brassicas on it in 2012 (in fact there are already some over-winter cabbages in the bed). Again, these need lots of nitrogen nutrients.

For the 2nd bed, I'm using the idea of 'three-layer grow through mulch' (Earth Care Manual, p.195), but adapting it. The 'three-layer' mulch first has cardboard or newspaper placed on the bed. Then manure is added, and then holes made plants, i.e. potatoes, planted though a hole. The 3rd layer is a mulch of grass mowings, straw, generally loose material, which helps contain moisture. This system is really used for when you are immediately added young plants/seed potatoes, not leaving it over winter.

For my experiment* I have added a layer of cardboard (after again doing my best to get rid of the perennial weeds), but instead of adding manure, I have thrown on all the left-over bits of plants. This includes everything from the remains of corn, chard/spinach I had dug up prior to it going to seed, carrot tops, broad bean and pea roots, the remains of the asparagus plants after cutting them down in autumn, etc. I then threw on some compost to help hold it down. The lottie is very exposed to wind and as the plant material is a bit light, I needed something to hold it down so it didn't just blow away.

*This isn't my own bright idea. I know I've read or heard about this, or something similar to it, a few years ago but cannot find where, so I'm unable to give the credit for the idea. I'm just using what I remember and adapting it to what I think might work.

Experiment 2: Showing the cardboard layer, then plant material on top.

I could put all the plant material in the compost and break it down that way as usual, but I wanted to see how it might go if I just add the material straight onto a bed in autumn. My thoughts were that maybe the frosts and snow will help break the plant material and cardboard down a bit, and then when it starts warming up in early Spring, I'm hoping the worms will get to work and start taking some of the material down into the soil.

At the very least, this mulch will help kill annual weeds and stop the soil from being bare and at risk of winds blowing away some of the good top soil over winter. If it doesn't break down enough, I don't loose anything as I can just pull up the plant material and put it in the compost bin, then add some standard compost back onto the cardboard and bed.

In nature, trees loose their leaves and just fall to the ground. It doesn't get raked up and put on a compost pile and then once broken down added back to the soil. It is left to do it's own thing and nature gets to work and over time it breaks down and releases all it's nutrients back into the soil. So I'm trying this because I was curious to see how much the plant material would break down over winter, when just left there as is, kind of mimicking nature a little bit.

The photos above were from mid-November. I'll be taking photos once a month over the next couple of months and report back how it is going.

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