Hugelkultur - composting in situ

I first read about hugelkultur at a serendipitously good time. I had just had to prune out damaged branches from both the plum and quince trees after a storm, and the wood was piling up next to the bonfire. Separately I was also trying to think of ways to irrigate the blueberries, housed in pots of ericaceous compost and sunk into the ground. At the same time, it was the start of the year and my perennial new year's resolution, to garden more sustainably and with less waste, was uppermost in my mind.

Hugelkultur is really a long - German for 'hill culture' - word to describe composting in place, which gardeners have been doing for generations, but layering the matter to be composted in a specific way to conserve moisture in the soil as well as providing slow-release nutrients for plants. 

It is also a good way to use woody waste - logs, brushwood, twigs - that might otherwise go on a bonfire, now that many of us are trying to move away from burning waste, specially in built-up areas.  

The photo at the top shows a finished hugelbed, planted up. They make an attactive garden or allotment feature in their own right; you could design a lovely curved hugel bed to add contours to your plot.

Constructing a raised bed using hugelkultur principles

1. Dig out a trench where you plan to build the hugel bed. Save the earth, etc, that you dig out, and if you're digging out turf, try to save it in blocks - you will need to replace it later.

Ideally you want to dig down to the water table, but 30-45cms is a good depth, the deeper the better. The trench should be wide enough to take good-sized tree logs, but not so wide that you won't be able to reach to the centre when it's built - no more than a metre. This will also give you room to bank up the sides gently.

2. Start filling the trench, first with the larger logs, branches, woody waste. If the wood has already started to rot a bit, then so much the better. Try not to use green wood which might start to sprout. The kinds of wood that you are likely to be cutting down or pruning on an allotment or in a garden such as ash, beech, birch, apple, pear, cedar and other conifers, are all suitable for a hugel bed. 

3. Pack the logs in as tightly as you can, even chopping them up a bit so they fit if necessary.   

4. The next layer to go on top is the brushwood, smaller branches, twigs, etc.

5. Next, pack into the trench any more organic matter you may have: straw, green leaves (not whole weeds), seaweed, if you live near the coast, mulch, leaf mould, grass clippings, anything tht might normally go on the compost heap.

7. Now turf the bed, the surface of which should now be at least at ground level if not slightly raised. This turf should in theory be the turf that you initially dug out of the ground to create the footprint of the bed. Lay it 'upside-down', ie, with the grass on the underside and the topsoil uppermost. This forms a firm base for the bed. 

8. Add a top layer of compost, about 8-10cms thick. You should now have a gently mounded raised bed, ready to sow or plant into.   

At this point, I have found that for purely practical reasons, my hugel beds have been more stable if I give them wooden sides as with a conventional raised bed. So they are not strictly orthodox, but the principles are the same.

How it works

The logs on the bottom layer absorb water, and once saturated, slowly release it, along with nitrogen and other nutrients as the logs slowly break down. The smaller branches and greeen waste break down more quickly into composted organic matter, feeding your plants.

The turf layer also breaks down, giving you a nice fine topsoil tilth to plant into. The top compost layer gives you a good starting point. 

Hugelkultur - pros and cons

+ sustainable and inexpensive - uses readily available - and free - materials;
+ provides slow-release nutrients for plants;
+ as the woody materials and organic matter breakdown, the process generates heat and warms the bed, giving you better germination and extending the growing season;
+ reduced need for watering.

- labour-intensive to set up and build;
- benefits may not be apparent the first year as your hugel settles down and continues to absorb nitrogen;
- banked sides may need support.

Having tested this out on the blueberries, last year I built a second hugel bed for the blackcurrant bushes grown from cuttings taken the previous year. Once everything was in situ, we then went through a three-month drought in the summer of course. The plants in the new hugelbed struggled a bit  - they were very young cuttings, after all, but in the established blueberry bed, I managed to get away without having to water them at all, and they survived.

Further reading

https://www.permaculture.co.uk/articles/the-many-benefits-of-hugelkultur/ - The Many Benefits of Hugelkultur

https://www.growveg.co.uk/guides/how-to-make-hugelkultur-beds-for-growing-vegetables/ - Growveg.co.uk

Through the keyhole - an African garden in London

A keyhole garden is a type of raised bed which originated in parts of Africa struck by droughts interspersed with torrential rain. The charity Send A Cow, which provides livestock and training in natural organic farming techniques to poverty-stricken parts of Africa, developed the keyhole garden as a sustainable way to help families to become more self-sufficient, to grow more vegetables in a restricted space, at very low cost, and reliably, despite the vagaries of the climate.

The basic principles are simple. The keyhole is a circular raised bed, with, crucially, a tube or basket in its centre which is filled with kitchen compost: peelings, outer leaves, eggshells, the usual stuff you throw in the compost bin. A pathway is cut out of the circle leading from the edge to the central basket so that you can easily refill the tube and indeed reach all parts of the keyhole garden with ease. Viewed from above the bed looks keyhole-shaped, hence the name.

Permaculture - sustainable gardening
The keyhole garden is meant to be as low-cost and sustainable as possible, so the bed is filled, lasagne style with various types of organic matter: cardboard (lots of cardboard), dried leaves and grass cuttings, coffee grounds, leaf mould, straw, newspaper, manure, wood ash, and only topped with a layer of topsoil to plant your first seeds or seedlings into.

The walls of the garden can be made from stones, rocks, bricks, anything you have to hand. A quick search on the web throws up keyhole gardens edged with old wine bottles, sandbags, car tyres, and wooden blocks.

Increased yields
To a large extent the keyhole garden looks after itself. The soil in  the bed is fed by nutrients from the compost breaking down and seeping from the central basket. You should only really need to water the central basket - in Africa, household grey water is used to keep the central basket moist - and the shape of the bed should ensure that water is distributed to the plants.

At 2 metres across - the maximum recommended diameter both for ease of access and to ensure plants near the perimeter still get moisture and nutrients form the central basket - the keyhole garden can reliably supply vegetables on a year-round basis.

I was intrigued by the pictures of different keyhole gardens in Lesotho and Uganda on the Send A Cow site and also at Inspiration Green, here.  Instantly appealing, some look as thought they have been thrown together, others more like permanent structures. As they use whatever materials are to hand and can be recycled, no two keyhole gardens look exactly the same. 

We may not have the specific challenges of poor thin soil and dry conditions that they do in Lesotho or Uganda, but the sustainability and permaculture aspects of the keyhole garden appealed very strongly to me, and I wanted to try building one on the plot. 

I see no reason why this idea of a central nutrient source shouldn't work in other raised beds as well. Obviously the circular shape of the keyhole garden means there are no hard-to-reach corners where the goodness from the compost never reaches, but the principle still holds good.

I always like the idea of specialist beds. Here is where the nutrient-rich growing medium will feed leafy salads, or get the tomatillos and/or physalis off to a flying start. The compactness of the keyhole garden also makes it easy to protect - from birds, or slugs, for example. Great for courgettes, too, for those whose conventional compost heap is a bit too stringy and uncomposted to successfully grow cucurbits.

The first task is to find an area for your keyhole garden and clear the ground, digging out any weeds and roots. There are no hard and fast rules about size. Send A Cow says that 2metres in diameter is a good workable maximum size. My cleared area didn't quite match that: the diameter here is 1.8metres.

To measure out the area of your keyhole garden, push a stick in the ground where the centre will be. Tie string to the stick and measure out enough string for the radius of your garden (90cm in my case). Tie the string at the other end to a second stick, then extend the stick out the full length of the string. If the ground is soft enough, you can drag the stick marking the circumference around the centre stick to make a line on the ground. The ground was pretty hard when I did this, so I marked the 90cm radius with pea sticks at intervals. I'm afraid you have to peer at this photo to spot the pea sticks but they are there.

Where the sticks have marked the circumference, start laying the external wall for the garden.

Here in north London we don't have a ready supply of boulders and rocky outcrops that they do in Lesotho, but what we do have is a lot of people making improvements to their properties. And where there are extensions being built, there will also be skips out in the road full of old bricks.

It took me just two skip-diving missions to find 40 bricks to line my keyhole garden and I didn't have to travel further than two miles from my front door. The rules say you should always ask for permission before removing anything from someone else's skip, and I'd go along with that. Apart from the etiquette aspect, once you've told the builder, or the householder, about your brick recycling project, they often offer help, whether it's just loading up the boot of your car with their bricks, or to tell you there's building work on the go just around the corner.

Next, add your central basket. Again, there is no precise material that should be used, so long as it's permeable. You can use sticks placed close together, you can weave your own with pliable canes such as willow, or you can reuse an old piece of wire mesh as I did here, bending it into a cylinder and securing with wire ties top and bottom. I also used the pea sticks to support and secure the mesh into position in the middle of the bed.

Now create the pathway that makes the keyhole shape of the bed, leading from the outside edge into the central basket. If it's feasible, it's a good idea to cut the keyhole path on the north side of the bed, the part of the bed that will be cooler and shadier, leaving the growing area sunny and south-facing.

Now it's time to start building up the bed. I used cardboard as my base layer: a good weed suppressant but also organic so it will decompose and help to enrich the soil. In Send A Cow's videos of keyhole gardens in Lesotho, they often scatter rusty tin cans over the base of the bed, to add iron to the soil. Here, newspaper covers any gaps in the cardboard.

As you fill the bed, you need to build up the sides as well. The bed can be as high as you like: these raised beds are great for people who can't bend down to ground level. The overall shape of the soil should be conical, with the soil level higher at the central basket and sloping downwards towards the outside the edge. The outer wall should rise above the soil level, otherwise soil will wash away over the sides when it rains. The next layer here comprises coffee grounds - Starbucks (and I'm sure the others do this as well) will bag up their leftover grounds for you to take away for free - and old grass cuttings ...

... and comfrey leaves for lots of good nutrients. But only the leaves - don't bury any root, unless of course you want to grow comfrey in the keyhole garden.

You can also add wood ash, leaf mould, manure. I added manure and then a tin layer of top soil to sow the seeds in.

The central basket has a smaller diameter than the recommended 30-50cm, but then the bed is smaller anyway. It does however need a lid to keep the kitchen compost from drying out: currently I have capped it with an upended coconut shell, so that the rainwater will still run down the sides of the coconut and into the basket. 

These Florence fennel seedlings were donated by a fellow allotmenteer and I've surrounded them with a copper anti-slug collar as a precautionary measure.

My resident allotment wreckers, the car and the fox, have been quite active over the last few weeks, so I added a net, lifted with hoops to keep them off the soil. Mr Tod, in particular, gets very excited by eggshells, and I really don't want to find the contents of the central basket scattered across the allotment. I may look for a more permanent framework and line it with fleece or clear polythene in the spring to create a keyhole greenhouse for early seedlings.

As well as the Florence fennel, I sowed seeds for two types of purple radish, Violet de Gournay and Hilds Blauer Herbst Und Winter , and some kailans (Chinese broccoli). These all germinated in 3-4 days and are growing strongly.

Further reading

• Send A Cow - the original keyhole garden project in Africa: http://www.sendacow.org.uk/lessonsfromafrica/resources/keyhole-gardens
• Dave's Garden - diagrams and detailed instructions: http://davesgarden.com/guides/articles/view/3726/#b
• Baker Institute - step-by-step diagrams and list of benefits: http://bakerinstitute.org/media/files/page/4d152358/khg_card_final_english.pdf. This page also lists plants recommended and not recommended for keyhole gardens. Under Not Recommended, tomatoes and squash are included, which is odd as many of the photos of keyhole gardens both in Africa and elsewhere, clearly show tomatoes and particularly squash growing happily in the beds.
• Inspiration Green - Different approaches to building keyhole gardens, in pictures: http://www.inspirationgreen.com/keyhole-gardens.html
• Permaculture Research Institute - a personal account of building a keyhole garden in Connecticut: http://permaculturenews.org/2011/04/07/building-a-raised-bed-keyhole-garden/

Videos

• Epic DIY - https://www.youtube.com/watch?v=SqL0NsgjVzg
• Send A Cow - building a keyhole garden in Uganda: https://www.youtube.com/watch?v=ykCXfjzfaco

The tracks of my tiers - why I love my double-raised beds

Last year I made a smallish bed raised high enough to grow carrots without having to protect against carrot fly – which doesn’t fly above around 2ft 6in, 3ft, or a metre, depending on which source you read. To be on the safe side I made my bed over a metre high. Also, because I felt that an awful lots of good organic matter was being buried deep in the base of this high box and going to waste, I created it as a tiered bed – essentially the high-rise carrot bed was a box set in the middle of a more conventionally sized raised bed. In this tier around the outside of the carrot box, I grew strawberries.

This two-tiered bed was a great success with both excellent strawberries and carrots – and then after the carrots were harvested, I transplanted radicchio and chicory seedlings to mature overwinter. It turned out that there were other advantages I hadn’t foreseen in having a raised bed inside a raised bed, and fired up by this, I made a three-tiered bed to go in a part-sunny, part-shady area in my garden this year.

Why make a tiered bed as opposed to a simple raised bed?

1. Carrots. The original tiered bed was designed to be high enough to grow carrots without them being troubled by carrot fly. Had I simply grown carrots in a 1m high box, a lot of soil would have been wasted filling the bed and it would be difficult to reach the middle of it to plants, weed and harvest.

2. Better access to light. The higher tiers get more sun. In my garden the back of the bed would be a damp and murky place were it not raised up to catch more sun.

3. Crop variety. It’s easier to adjust the soil to suit the crop in each tier. With carrots again, the soil in the top tier where the carrots are grown can have sand added to it which doesn’t affect the soil in the lower tiers which may have bonemeal added for strawberries, or manure for Chinese broccoli.

4. Crop rotation. Following on from variety above, crops can be ‘micro-rotated’ within the tiered bed with ease.

5. Warmth. The raised sides of each tier can reflect warmth on to the growing crops. This can be accentuated by painting the sides white, or even coating with silver foil.

6. Weed-free. Maybe this is down more to ground preparation but I find the tiered bed is to all intents and purposes weed-free, more so even than a conventional raised bed.

7. Aesthetically pleasing. A tiered bed does look smart, even a bit of a talking point. And in my narrow garden, the tiered bed gives the impression of width. I’m sure an artist could explain why.

Now, out of sheer laziness, I find myself beyond the point of no return in building a massive three-tiered bed on the allotment. I measured up a corner of the bed just under the asparagus where the slope makes it shady and prone to poor drainage – both problems which will be nicely alleviated by a raised bed – and then decided I couldn’t be bothered to cut all the gravel boards to fit, so might as well just use 2.4m boards for the base uncut. That base has now gone down and it’s HUGE. This year as well as carrots in the top, I’ll plant out the courgettes in the lower tiers – I can fill these with lot of kitchen compost which the courgettes like.