Using Composting Raised Beds

Years ago, when I first started growing my own vegetables, I mentioned to a couple of old boys that I’d like to try growing courgettes and both of them said I should “just stick them in a compost heap and you’ll get great ones, better than in the ground”.
What a great idea I thought, immediate re-cycling. I love the things old boys come out with.
But what would I do with all my accumulating compost meanwhile? Isn’t that what a compost heap is for, a place to put your compost? Where’s it all going to go while my ‘land of the giants’ courgettes are taking over the compost heap?

My newly acquired plot of overgrown land, my future allotment, was generating mountains of compost, as a result of clearing weeds and scrub, so what would I do with all that vegetation once the main compost heap became a growing space during summer?

I decided the solution was to build a dedicated raised composting bed for all this material, so that the compost was contained, and could then be treated as just another raised bed during summer. This would be better than the sprawling compost beds of sprouting weeds and seeds I had seen elsewhere on allotments. I used some old pallets for the experiment.

The first composting bed, made from old pallets, acquiring its first load of fresh compost

 

All the new compost material, generated when the raised composting bed was hosting a crop, would be temporarily collected in compost bins during the summer.
And so I planted courgettes in the new raised bed, directly into the compost, and they were indeed very successful. I saved any new compostable material in compost bins during the summer as planned. Once the courgettes had finished I removed the compost from the bed, dried it, riddled it, and bagged it up for use as potting compost the following spring thus giving it another purpose.
This all worked so well that the raised bed evolved, acquiring a loosely fitting glass top to assist with composting, and to protect young, newly planted courgette plants, thus allowing me to plant them out a few weeks earlier.

The seedlings are planted at the back and an old carpet stops weed growth. Glass is rested on top to protect the young plants and give them a good start.

 

When warmer weather comes the glass is removed. Then the carpet holds in moisture, and will prevent the fruit from touching the compost

 

Once things have warmed up the plants grow forward across the carpet.

 

Once the plants have died off in late summer I just repeated the process, transferring the contents of compost bins into the composting bed, making a new foundation for next years courgettes. I repeat this process annually which allows me to grow courgettes in the same place every year.
It has also allowed me to create a composting cycle which produces two crops, and lots of compost. More on this below.

The system works so well that, by the third year, the original and slightly rotting pallet sided bed was eventually superseded by a new, but similar purpose built bed in a different location. This was made from discarded metal roofing sheets, and added a removable front for easy compost removal.

This is now very definitely a permanent fixture. It has sloping sides for glass, and a removable plank front, like the original, for easy access.

The new composting raised bed. Sloping sides provide rests for glass sheets. The removable boards at the front hold the compost in place until it settles down. The boards also allow access during compost removal

 

 

This composting process has allowed me to develop a four year composting cycle. Descriptions below:

 

YEAR 1 – gathering and initial composting
Compost material is gathered in compost bins during the summer, where it partially composts, and is then moved to the composting bed during autumn and winter. Fresh animal manure can also be added at this time, either mixed in but also on top to cap off any potential sprouting of weeds. The capping off can be done using old carpet instead, or weed textile material, but a top layer of manure is desirable.

During the transfer process the summer gathered compost within the bins is automatically turned and mixed as it is transferred and added to the bed.

Nothing is going to be planted in the composting bed until early next summer, not for at least 4 months, so there’s plenty of time for any fresh compost and or fresh manure to break down.

The bed is filled with compost over winter. Carpet is put on top until the new plants are ready to go into the bed.

 

 

YEAR 2 – courgette year (1st crop)
In early summer of year 2 courgettes or squash are planted directly into the compost at the back of the bed so that they can grow forward across it. Leave the carpet in place to reduce moisture loss and to prevent the fruits from coming into contact with organic material (which sometimes triggers rotting).

The courgettes are planted (along with sunflowers, a mistake as it turns out). The glass is put over for protection and once the plants get going the glass is removed and a few of the front boards are removed to allow the plant to ‘spill’ forward out of the bed towards the end of its life.

 

The courgette plants grow out over the carpet which keeps the courgettes clean and healthy

 

At the end of the season (autumn), when the crop has died off, the compost is removed from the bed, dried (optional) and riddled (optional), then and stored in sacks or bins over winter. Drying halts the composting, kills of any undesirables and allows you to keep the compost for a long time. Riddling takes out the big lumps and un-composted twigs. However, if you know you are going to use the compost in towers, big pots, or containers then just keep it in sacks until required, without drying or riddling.

This removed bed compost will now be over a year old (and therefore well rotted).

Digging out the compost which is now a year old

 

 

I partly dry the compost by replacing the glass on the composting bed, after the plants are finished, so that it keeps off the rain and creates a greenhouse effect. Once partly dry it goes into sacks for storage, or onto further drying.
I try to dry some of the compost outside, before the end of summer, while it is still warm and breezy, but you could save the compost in sacks and dry it in the greenhouse during winter if you like, when you have more time and space. I always end up doing this with some of the compost anyway.
I spread the compost on black sheets, or on black watering trays to dry. I mix up the compost occasionally (by raking) to bring the damp compost to the top, and to speed up drying. The warmth, light and moisture encourages any remaining seeds to sprout, and then they perish in the raking, and in the increasingly arid conditions. Worms depart of their own accord.
The compost does not have to be completely dry, just dry enough to stop it composting, and to kill off any stowaways (e.g. tiny slugs and eggs).

Compost drying on sheets, or in trays in the poly tunnel or greenhouse, then some of it is riddled into sacks or bins to be used as potting compost.

 

You don’t have to riddle it all, just enough for potting use. If you are going to use the compost in potato towers or large pots then you can leave it rough as it will continue to break down during the next growing season in the pots or towers. The rough and lumpy bits will be an advantage when the compost is used in large quantities (e.g. in large pots or towers) as they will add texture and discourage the finer material from packing down and becoming ‘muddy’.

 

Once all the rotted compost is removed from the bed then the freshly gathered compost, which has been gently composting in the compost bins during the summer, is moved to the now empty composting bed in autumn. This new input completes the annual cycle of the bed, and allows courgettes to be grown in the same place every year and in new compost. Continue this cycle annually, forever.

But it doesn’t end there. The compost you have created goes onto be used elsewhere.

 

 

YEAR 3 – potting and potato year (2nd crop)
In compost year 3 the stored compost (dried or not) is used in several ways, including the growing of a second crop.

 

A – Potting compost.
I use the dried and riddled compost in the bottom three quarters of pots and top them off with a little bought compost to prevent weed seeds sprouting. I save a small fortune on potting compost.

Dried and riddled compost

 

B – Poly tunnel container spuds
Spuds are planted in containers (big plant pots in my case) full of home made compost. This is done in January, and the pots are put in the greenhouse or poly tunnel. They happily sprout in there, usually in February, and I harvest the first potatoes in May. The pot grown spuds keep me going until the outdoor planted potatoes are ready for harvest thus extending my potato harvest season by months.

Potato plants in pots in my poly tunnel (month)

 

 

C – Potato Towers
The rough compost, riddled or not, dried or not, is stored over winter in sacks and bins. When needed it is mixed with a little well rotted horse manure and put into potato towers.

Towers made from old tyres, plastic barrels and old life rings are great for spuds, save space, and are easy to harvest.

 

A potato tower made from old tyres and ready to receive soil and/or compost

 

The compost continues to break down into finer particles throughout this season.

 

 

YEAR 4 – mulching year
The pots and towers are turned out onto beds at the end of year 3, or at the start of year 4. Thus the compost material, gathered up to 3 years before, now ends up in your beds as mulch where it helps to discourage weed growth, condition the soil, and contributes to the production of a third crop.

 

 

Advantages of the composting raised bed system:

1 – Greater self-sufficiency (compost).

2 – Total control of what goes into your potting compost (e.g. chemical free).

3 – Two impressive crops from each batch of compost.

4 – Courgettes are grown in the same sunny place every year, no rotation required.

5 – Courgettes grown in good compost will greatly out perform courgettes grown anywhere else. So less plants needed, less space used.

6 – Potatoes are grown in the same place each year (either in towers or pots) and vertically, thus saving space. No crop rotation required.

7 – The combination of composting raised beds and potato towers are productive space saving methods which are very suitable for the grower with limited space, especially if you have access to lots of vegetative material.

8 – The compost bed and potato towers also make excellent all year round worm farms.

9 – The height of the composting bed makes for easy searching and harvesting of courgettes.

10 – During the harvesting of potatoes from pots and towers those pesky little peas sized spuds are easy to find and remove so that they don’t pop up again next year.

11 – No wasted material as any surplus compost is simply mulched onto beds, at any stage, even the rough, lumpy stuff removed during riddling.

 

 

Some other points to consider:

A – Crop choices – I usually use the compost to grow a crop of courgettes/squash followed by a crop of potatoes, but you could grow any two main crops of your choice using the same system, in the same compost, as long as they aren’t from the same family. I have successfully grown garlic and onions in large pots using only my compost.
Also I have grown runner beans and tall peas on vertical poles at the back of the raised bed at the same time as the courgettes, thus giving me an extra small crop.

 

B – A warmer bed – In order to plant young seedlings earlier in the year you can mix in some fresh horse manure a week before planting and the compost will begin to generate gentle heat which will encourage growth and reduce the chance of frost damage.
Alternatively add glass above to keep cold winds and frosts at bay, and to increase daytime warmth.
Do both for amazing results.

 

C – Floor lining – The floor of my composting bed is lined with porous material (old builders sacks) to prevent mole and bank vole incursion, and the constant uprooting of the plants. The floor textile is covered with an inch of soil to hold the sheet in place and to give worms cover. This ‘enriched’ and wormy soil layer remains in the bed as a starter culture for next year’s compost.

 

D – Size to suit you – Make the bed to the same size of any sheets of glass you already posses so that it can also become a cold frame. A composting raised bed can be any size and can even be made using a large container. I have purposely constructed my single composting bed to accommodate two courgette plants but you could have two or more smaller containers if you prefer.

 

E – Alternative to compost bins – I have lots of composting bins now (donated over a period of years) but before I acquired them I saved my summer compost in discarded 1 ton builders bulk material lifting bags (a space saving (vertical) compost storage system).

 

F – Watering tubes – I now use old drain pipe as watering tubes so that moisture is not splashed onto the plants. These are pushed into the compost either side of the plants and the water goes directly to the roots. The surface remains dry, discouraging mould, rot and slugs. I have cut holes in a bed width length of carpet, 3 for watering tubes and two for the courgette seedlings to be planted into.

Watering tubes being inserted through 3 holes in the carpet.

 

Watering tubes in place, and folds in the carpet (see note below)

 

 

G – Carpet folds – If you use a single piece of carpet it will, during a rain shower, at least for a while act like a roof, shedding valuable water off the bed and onto the floor. I make horizontal folds in the carpet to catch and retain rainwater, and to give it time to soak through into the bed below.

Carpet folds catch rainwater (prevent it from running off).

 

Have a go, see what you think.

 

 

Andrew

 

 

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