One thing I have been asked about a number of times at my site and elsewhere has been about the lasagne gardening concept. I therefore thought I would share my experiences of this fantastic method of tackling a new allotment, or simply as a no-dig approach to fruit and vegetable growing.
Popular in the US, this concept was something I happened upon when I first took over plot 39 in the middle of a particularly dry June in 2010. When we took over the plot, the clay soil was as hard as rock. We tried (and failed) to dig the soil over with a border fork, and ended up with a broken garden fork and bad backs for our efforts!
I therefore did some internet research and found out more about lasagne gardening which seemed like the answer to our dreams.
You can either build up your lasagne beds in the autumn, to rot down over winter ready for spring; or build them up and use them immediately. I usually use them up to plant in immediately - mainly because I have used this concept where I have taken over a plot mid-summer and wanted to get some crops from the plot asap.
Lasagne gardening uses the same components that a good compost heap uses: green materials (grass clippings, uncooked kitchen vegetable peelings and trimmings, tea bags, coffee grounds and filter papers, sea weed, horse, cow, rabbit or chicken manure, annual weeds without seeds or flower heads) and brown materials (shredded bark chippings, newspaper, cardboard, drier materials such as leaves and straw/hay).
The process is simple. If you can, fork your soil lightly - simply by pushing your fork into the soil and wiggling the fork backwards and forwards to open up the soil texture - thus easing any compaction already in the soil.
This step isn't completely essential. If your soil is too hard to get a fork into, this can be left but you will need to do it at the end of the season after harvesting or you will experience compacting over time and your bed could be liable to flooding and the long-term health of the soil could be affected.
You then start building your bed by clearing away any large perennial weeds (such as nettles, dock, thistles, dandelions, large bindweed plants, etc) from the ground. Once this is done, lay your cardboard over the top of the remaining weeds in the area you wish to set up your bed. Thoroughly soak the cardboard with water, overlapping the cardboard by at least 15 cm to ensure weeds don't grow between. This initial layer will suppress the weeds.
You then start by piling materials of the green category on top of the cardboard. I recommend starting with manure. You then add something from the brown category and then alternate layers. Each green layer should be about half the depth of the brown layers. Continue adding your lasagne layers until you are happy with the height of the bed, or you have run out of materials. As you add each layer, water each layer copiously, this ensures the bed isn't too dry.
Finish your bed off with a layer of compost. Plant your plants into this layer.
Over time, the bed will rot down and gradually shrink in height. It is a good way to fill a raised bed or tackle a plot when you are feeling a little overwhelmed by the weeds.
Once you have harvested the bed, you can simply add another layer of newspaper and top with more green and brown layers ready for the next season - no need to dig. However, if you decide you would like to dig over the bed, you should discover nicely rotted layers with a rich, fluffy texture and plenty of earthworms.
Some lessons I have learned through trial and error:
1) If your soil is dry as my clay was in June 2010, thoroughly water the soil before covering with the first layer of cardboard and then ensure you thoroughly soak each layer added with water. This provides a dark, moist area to attract earthworms that will loosen up the soil as they tunnel through it. On one of my first beds I built, I didn't soak the layers enough and I found the bed got infested with ants and woodlice which ate everything! In addition, it can prevent the layers from rotting down equally, which means the plants won't benefit from the composted layer.
2) If you are intending on leaving your bed to rot down for a couple of months prior to planting, you can use slightly less composted manure. If you plant to plant immediately into the bed, ensure the manure isn't too fresh as it is likely that the high nitrogen content will cause the bed to heat up too much - causing scorching of the plant roots.
3) Ensure you remove large perennial weeds prior to starting. I have tried building the beds removing these weeds and not removing them, I found that, despite the number of layers, it is not deep enough to stop these continuing to grow. You will simply be saving up a problem to deal with later and the weeds will not be weakened very much. I have found that starting up lasagne beds over couch will kill the majority of the couch off. You may have to selectively pull some plants out at the end of the season or when harvesting, but over time, the couch is weakened and dies off.
4) You may wish to apply a wet newspaper layer over the top of the compost, planting through this to further keep any weeds down and retain any moisture. This is particularly useful if you use your own home-made compost that is likely to contains some weed seeds.
5) As mentioned, I garden on clay. However, I have had good reports from fellow gardeners who have tried this method on their sandy soils that this method helps the soil retain moisture - great news in a dry summer.
Lasagne Bed in Action
In late May 2012, we took over plot 37 which was in an overgrown state. As with the original plot, the soil was very hard due to little rain over the previous winter. We therefore decided to utilise the lasagne bed method to develop this plot.
1. The state of the plot we took over in May 2012. Here, we are cutting down the high grass with shears, so we could see if there was anything worth saving on the existing plot.
2. With the first lasagne bed built, and weed suppressant over the grass for the paths. We have also cleared the front bed which was an existing strawberry bed and had been well cultivated in the past. The blue tarpaulin covers up the remaining weeds to weaken them.
3. The plot mid-June 2012. By now, we have introduced another lasagne bed and both have been planted up with summer and winter squash plants. Wind protection has been added to protect the young plants whilst they are settling.
4. October 2012. The beds are producing well. The cosmos plants added have grown fully and continue flowering right until Christmas.