Birchwood Fire Station Raised Beds

A few years ago I was asked to advise firemen at Birchwood Fire Brigade Station as they wished to grow organic vegetables and invite local schools to tend the crops. When I visited I noticed that they had been pruning and cutting the trees surrounding the station. They looked at me as if I was from another planet when I suggested they could use their tree trunks, logs, branches, roots and shrubs inside the raised beds! Then fill them with manure and compost.

Horse manure

The next stage in the development was to fill much deeper raised beds with FRESH wood chips directly, say 2/3 full. Different-sized chipping help and mixed with larger pieces of wood all help to stop it from settling down and compacting, as sawdust tends to do. Adding horse manure on top of the woodchips helps to provide the nitrogen needed to rot the woodchips as they contain lignin and cellulose. Then topped up well-rotted garden compost, deep enough for most vegetables so as not to deprive them of nitrogen as the wood material rots. This was successful although I realised that compost does not in itself contain the same minerals as soil, so I powdered the compost surface with Rock Dust and dried seaweed. Plants were regularly fed a solution of liquid seaweed.

Adding Earthworms

Selective earthworm species were added to the Worm Towers to ‘ignite’ the beds and soon they were teeming with earthworms, making a very productive system. Believe me, this works! It is like having a huge Waste Buster wormery,  without the window!

Role of earthworms

Darwin wrote in his book, ‘The Formation of Vegetable Mould’, “It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures.” But why would he say that?

Earthworms are an important part of the soil ecosystem. They mix the organic matter and mineral content of the soils helping the penetration and movement of water, air and nutrients from which plants and soil organisms benefit. They increase microbial activity which facilitates the recycling of nutrients/minerals into forms more readily available to plant roots. Earthworms increase humus in the beds. The raised bed literally becomes a huge wormery full of worm activity which in turn utilises the benefits of a vermicompost enriched soil.

Tree trunks and tree branches Hugelkultur style

Being much larger they take much longer to break down. They are ideal if your allotment, veg growing area, etc., is next to large trees or bushes that need pruning, but transportation to your garden could be an issue. If used I would suggest filling in the gaps as they are loaded into the bed with woodchips and with a layer of horse manure over them. Woodchips provide more areas for the microbes to work on them and increase in population. See Hugelkulture and its benefits with an article well worth reading about by Alys Fowler

You will see the results in the video.

Woodchips 

Personally,  I prefer the woodchip method.  At this time of the year, it is easy to obtain as parks, gardens, etc., shred the trees. You often see piles of woodchips just lying there rotting down in parks, so ask the rangers for some to bag up. Or ask a local tree surgeon to drop some off for you. I prefer woodchips as a moisture sump now to adding just garden compost, which tends to dry out quickly. The woodchips have the advantage that being chopped into pieces that are larger than garden compost, they soak up and retain the moisture better. Woodchips under the top layer used as a path are already covered with the essential digesting microbes and may also contain humus by now. They are ideal to recycle and top up the beds which over time will settle down as the materials decompose. The downside is that they need an annual topping up over the winter. This helps to protect your soil surface and helps them to rot down when in contact with the moist soil.

Preferred option. Building initial layers

From the ground up, woodchips, 2/3rds of the height, manure/grass/weeds layered on top, remaining height filled with course garden compost, with 3-4 inches of sieved garden compost or sieved woodchip path material, topped off with a mixture of worm compost, leafmould and seaweed with rock dust and initially a few hand full of soil. It can be gently raked into the top surface if about to sow or left sprinkled on the surface over winter to find its own way down into the soil. This is ideal for seeds.

So how does this system work?

In simple terms, microbes break down the contents of the raised beds, earthworms do likewise. This action makes minerals available to the plants that they take up we obtain when we eat them! There is a lot of science involved so let’s unpack it! First, let’s look at what we have.

Minerals in soils

Many of you know the difference between soil and compost. Fresh compost is in the main, depending upon how you make it and what you add, organic matter and living organisms. Soils contain living organisms, organic matter, humus and rock particles. The rock particles contain the mineral elements, such as iron and phosphate. It is known rocks are broken down into smaller particles by several processes, known as direct weathering. Prime examples are water freezing and cracking the rock, (physical weathering), and rock particles dissolving in acidic rainwater, (chemical weathering). Indirect methods of rock breakdown included biological weathering, whereby in moist environments mosses and lichens slowly break down the rock surfaces and acids released by plants or in leaf litter. Using my method we do not have much soil.

Rock Dust

As you will be aware, garden compost/woodchip compost is organic matter which has been decomposed by microbes, fungi, earthworms etc. It may contain trace minerals it absorbed whilst a plant that it acquired from the soil it grew in. As mentioned soil particles contain minerals obtained from rocks. In the absence of soil, as in my raised beds, earthworms will consume rock dust, and use it to help them grind the organic matter they consume in their gut, a ground-down volcanic rock. I use a Soil Association Accredited called Remin which is from a sustainable source. Being finely ground up dust, they use it to grind up organic matter in their gizzards, (having no teeth!) thereby distributing the rock minerals around the beds in their casts. Rock dust is also added to my Waste Buster wormeries.

Humus

Of course, you could add quality topsoil to your beds and there is no harm in that. Personally, I prefer to keep the topsoil where it is found, not have to transport it to my garden and pay for it! Soil is a natural product and may contain humus whereas garden compost is man-made and will eventually contain humus as the compost is broken down and stabilised to a point when the original material is no longer recognisable. I suppose it is the glue that binds the tiny soil particles together whereas sand will simply run through your fingers as its humus content is likely to be low or even nil. Humus retains water and nutrients/minerals and is excreted by earthworms after feeding upon decaying matter.

Role of microbes

Recent research, however, has found another direct weathering of rocks, undertaken by microbes, microbial mineral weathering. Bacteria and fungi have been found to use a variety of mechanisms to release minerals from rocks, which is known as bio-fertilisation. They play an essential role by actively contributing to the release of key mineral nutrients that are not only required for their own nutrition, they are also needed by plants (just like we need minerals!)

Their role in raised beds

Specialist fungi break down the lignin and cellulose in the woodchips and other microbes and bacteria have their part to play. These microscopic soil life organisms are the processors in the soil and earthworms are major facilitators. Microbes are food for earthworms. Yes, earthworms are in effect predators upon soil microbes! Thus earthworms love the woodchips/horse manure mix as well and populations increase. Annual autumn prunings/weeds from my own garden are shredded and go directly into my raised beds.

Potato no-dig system

Trees, logs, branches, or fresh woodchips, topped with manure, grass/weeds and as above, with the addition of cardboard if growing potatoes, topped with a black woven material to stop light as seen in the video. The only reason we ‘earth’ potatoes up is to stop the sunlight from turning the potatoes green. This method also stops weed growth. A win-win situation!

Although great inside the beds, I would not advocate a woodchip mulch around plants and this could be a haven for slugs to shelter. Unless of course, you are sure you can correctly use a suitable barrier around your beds to stop them entering. Many are available.

Sowing crops

I do prefer to transplant many of my crops, including onions, peas, and beans, which I grow in Rootrainers. I even multi-sow radish and spring onions in them and then transplant them. Carrots unless they are small round carrots which I no longer grow, are not ideal for transplanting. If you prefer to sow seeds, then season permitting, it is a good idea to plant on a loose friable surface allowing the seed roots to establish themselves before the beds have settled. If not plant wintergreen manures instead of leaving the soil bare and nutrients washing out. As the soil level settles and spring is nearing, lay cardboard or a black woven material over the green manures to kill them then you do not have to disturb the soil microbes as you would if you dig them in. Mustard is easily killed by frosts and is another choice. When ready to sow, peel back the black sun-absorbing woven material, as required and simply add some more sieved compost or leaf mould on the surface in which to sow.

Update. 11/3/20 I have not visited the Birchwood Fire station for some time and it may not be having school visitors any more.