Back in May of 2016, I published an article on an experimental polyculture for meeting the fertility demands of the fruits, nuts, herbs and perennial vegetables on our plot without relying on animal manures and imported compost. We called this polyculture the biomass belt.
You can find the original biomass belt article here. Four years later we have had a chance to see how the polyculture has performed and have learned a thing or two about the way the plants interact with each other, what works and what does not. During this post, I’ll be revising the design based on our observations and presenting a version of the design that appears to be working well in our polyculture market garden.
I’ll start with an introduction to the polyculture and the species involved and go through the design considerations, development, and management practices for this polyculture. We’ll look at how the polyculture has developed in our garden and how you can purchase the plants (or seeds and cuttings) from our nursery should you wish to try growing this polyculture in your own garden.
So let’s start with what is the Biomass Belt.
What Is The Biomass Belt ?
How Does It Work?
The polyculture is composed of mineral accumulating comfrey in raised beds, Nitrogen fixing ground cover sown into pathways and a Nitrogen fixing hedgerow.
|Illustration by Georgi Pavlov|
|Illustration by Georgi Pavlov|
The Nitrogen hungry comfrey is fed with the biomass from Nitrogen fixing plants, that through a partnership with soil micro-organisms can convert atmospheric Nitrogen into Nitrogen fertilisers useful to themselves, but also becoming available to neighbouring plants. For more on Nitrogen fixation see here.
|Illustration by Georgi Pavlov|
Each time the path vegetation and hedge are cut, root tissue underground is shed in to the soil providing significant quantities of organic matter and nutrients to the plants.
In summary, the unique ability of the Comfrey to feed deep and produce copious quantities of biomass is utilized to provide nutrients to main crops whilst the pathway ground cover and hedgerow’s unique ability to fix Nitrogen is utilized to provide nutrients to the comfrey.
|Illustration by Georgi Pavlov|
What follows is a design guide covering how to select a site for this polyculture, a close look at each component of the design and the species within each component, and what I hope are clear and concise instructions to build and manage this polyculture. At the end of the post you can find a summary table of the plant species, a brief description of how we have set up this polyculture in our Polyculture Market Garden and a link to purchase the polyculture from our bio nursery in plant or seed form.
Light demands – For optimal growth, the polyculture should be orientated along the west-east axis and be to the north of any light demanding crops to reduce shading. The plants we have selected below will grow in partial shade and on other orientations but will yield less biomass as a result.
Water – Adequate irrigation is a key to healthy and productive plants. This polyculture is not well suited to semi wetlands and areas with a high water table and will not thrive in very dry areas with no access to irrigation. In dryland/climate, selecting a position for the polyculture that requires as little irrigation as possible is essential and can be achieved by planting on contour and using simple earthworks to keep rainwater around the root zones of plants.
N.B. All of the plants we have included in the polyculture are drought tolerant (Trifolium repens – White Clover to a lesser extent) and will survive long periods without water once established, but will not produce high yields of biomass in these conditions.
Subsoil Mining – Siting the biomass patch, specifically the comfrey beds, below compost toilets/manure piles and areas that are likely to receive nontoxic leachate will help prevent the loss of nutrients draining off-site.
Proximity to crops – Consider the distance between your beds and where you need to apply the mulch or prepare and store the liquid fertilizer. If growing comfrey for mulch it probably doesn’t make much sense having to haul the material over large distances.
Species Selection – Species selection should take into account the following;
- Climatic compatibility with the site
- Drought tolerance
- Speed of growth i.e fast-growing
- Tolerance of hard pruning
- Benefits to wildlife
Raised beds are a major part of our fertility strategy and when managed properly overtime they retain water and nutrients very efficiently. This polyculture can include one or two 1.3 m wide raised beds for comfrey surrounded by 50 cm paths and a 70 cm wide raised bed for the Nitrogen fixing hedge. It’s important never to tread on the soil of a raised bed and the above dimensions allow reach within the beds from the pathways. The bed length can be as long as best fits your site and needs. The following illustrations and photographs are based on a 10 m long section of this polyculture.
|Example Perennial Polyculture – The Biomass Belt – Bed Layout|
To form the beds the area should be cleared of all plants, best achieved in most situations by sheet mulching with ample organic matter 6 months prior to planting. Pernicious perennials such as wild brambles – Rubus fruticosus and couch grass – Elymus repens should be dug out before mulching and the soil should be forked over as deeply as possible with a strong garden fork.
If you have a heavy clay compact soil it’s best to double dig and incorporate plenty of organic matter (20- 40 L m2) into the comfrey beds before planting.
|The right shape shovel for forming paths|
Once you have cleared the whole area of weeds and forked it over to relieve compaction, mark out the bed shapes with string and dig out a 10cm layer of soil 50cm wide to create paths around the bed, applying the soil to the surface of the planting area and thereby creating a raised section of earth that will be your bed. A flat bottomed shovel is a good tool for this job.
|The beds with corners pegged and string attached|
If you are not sheet mulching, remove all weeds, fork over the beds, cut out the pathways and apply 20 L of compost per m length of the comfrey beds and 5 L to the nitrogen-fixing hedge bed. The compost should be applied to the surface and topped with a 20 cm layer of mulch.
|The biomass belt beds, forked over with compost and mulch applied – Photo by Trisha Franke|
The beds are now ready for planting and the paths for sowing.
A side note when path forming – We are fortunate to have access to a stream that we can divert into the site and we flood paths for irrigation. When establishing the paths we alter the depth and gradient to facilitate the required movement of water within the polyculture. The slower the water travels along the paths the less erosion there will be. Capillary action draws the water deep into the beds and underground.
Below you will find a closer look at each component in further detail based on a version of this design we have implemented in our Market Garden
The Polyculture Components
- Nitrogen Fixing Hedge
- Nitrogen Fixing Ground Cover
- Comfrey Bed
1. Nitrogen Fixing Hedge
The Nitrogen fixing hedge supplies a significant biological source of Nitrogen and biomass, habitat for wildlife including a number of beneficial species, and makes an excellent living boundary/fence on the perimeter of a site or as a subdivision within a site.
The hedge is composed of two species of nitrogen-fixing shrubs Elaeagnus angustifolia – Russian Olive and Elaeagnus umbellata – Autumn Olive and one the fastest-growing plants in the temperate zone Miscanthus x giganteus – Giant Miscanthus.
Below is a design illustration of a mature Nitrogen fixing hedge.
Maintaining The Nitrogen Fixing Hedge
Formative Pruning and Trimming – If planting out single stemmed whips, the following formative pruning is necessary during or after planting out. Cut up to 1/3rd off from the top of the whips. The cut should be made just above a node and at a 45-degree angle. This will encourage the plant to form a multi-stemmed crown. The following year the tips of each of the multi stems can be cut again encouraging further branching. Once the plants have developed full crowns they can be trimmed to reduce width and to the desired height at least once per year. After trimming, the arisings can be raked onto the comfrey bed. The Miscanthus plants can be cut annually with the stems chopped up into 10-20 pieces and placed on the comfrey beds.
The best time to trim the hedge is early winter when the comfrey is dormant and mid-summer after the comfrey has been cut. The summer cut avoids disturbing nesting birds and provides mulch during the dry season.
|The biomass belt in Year 4 with the hedgerow forming nicely|
Feeding – These plants will not require any feeding, however, mulching with a 30 cm diameter mulch mat or card/straw mulch whilst the plants are establishing for the first 2-3 years will be beneficial both in reducing irrigation needs and preventing weed competition.
Irrigation – The first season after planting, irrigation should be applied when the soil beneath the mulch is dry. In the following years irrigation is only necessary during very dry summers and should be applied before the plants begin to wilt. The plants will grow much faster and produce significantly more biomass if they have a good supply of water.
Native wild plants that emerge around the shrubs can be left to grow freely once the shrubs have matured and if they are not directly competing.
Nitrogen Fixing Hedge – Species Overview
Elaeagnus umbellata – Autumn Olive
|Permaculture Plant – Elaeagnus umbellata|
Overview: A large deciduous shrub from E.Asia, growing 4.5 m high and 4.5 m wide, hardy to zone 3 (-35C) tolerates part shade, very drought tolerant. Branches are often thorny, leaves are bright green and silvery beneath. Yellowish white, fragrant flowers are produced in May-June, followed by rounded silvery brown (ripening red) fruits in Sep-Oct. Sometimes cultivated for its edible fruit. There are many named cultivars. Flowers are rich nectar and very aromatic. Plants can fruit in 5 yrs from seed. This specie is considered invasive in the U.S
Uses: Edible fruit raw or cooked which is very tasty and can be made into jams, preserves etc. The fruit contains about 8.3% sugars. 4.5% protein. 12 mg per 100 mg Vitamin C. The harvested fruit stores for approximately 15 days at room temperature. It can be used as a hedge plant and tolerates maritime exposure succeeding in the most exposed positions. The nectar from the flowers is attractive to bees comprising 28% sugars. The plant is used as a nurse tree, when planted with fruit trees it is reported to increase the overall yield of the orchard by 10%. It can also be grown as a biomass crop on a 3 year rotation.
Nitrogen Fixing Potential: The species is classified by USDA as being a MEDIUM nitrogen fixer with estimated yields of 85-160lbs/acre or 39-72kg/4050m² or 0.014g /m2.
Propagation: Seed – best sown as soon as it is ripe in a cold frame. It should germinate in late winter or early spring, though it may take 18 months. Stored seed can be very slow to germinate, often taking more than 18 months. A warm stratification for 4 weeks followed by 12 weeks cold stratification can help. The seed usually (eventually) germinates quite well. Prick out the seedlings into individual pot as soon as they are large enough to handle and plant out when they are at least 15 cm tall.
Planting Material – 3 year old plants will provide an instant hedge effect but can prove expensive when planting out large areas. 1st year whips are cost effective and with proper pruning and some attention during the first few years of development will quickly fill out.
These plants can be grown from seed although may take up to 18 months to germinate. Once they do germinate they can be ready to plant out 7-8 months later and can starting providing good quantities of biomass within a few years.
We supply Elaeagnus umbellata seeds and 1st year saplings from our plant nursery – Click here for more info.
Elaeagnus angustfolia – Oleaster, Russian Olive
Overview:A deciduous large shrub or small tree from Europe and W.Asia, growing approx 7m high and 7m wide. Hardy to zone 2 (-40C), tolerates part shade, salt and air pollution.
It has silvery branches often thorny, with silvery scales when young, silvery willow-like leaves, silvery flowers in June and yellowish-silvery fruits ripening in October. Plants prefer continental climate.
This specie is often cultivated in Europe and Asia for its edible fruits (there are many named varieties some of which are thorn less). The plants begin to flower and fruit from three years old. It is very tolerant of pruning even right back into old wood. The flowers are sweetly scented. Fruits hang on the plant for much of the winter providing a valuable source of winter food for birds. The fruit is readily eaten and disseminated by many species of birds. This species is considered invasive in the United States.
Uses: Edible fruit -raw or cooked as a seasoning in soups. The taste is dry sweet and mealy. The oval fruits are about 10mm long and contain 17 amino acids with total sugars making 54%of the composition. In China they are made into a beverage
Expected fruit yields are 7-9kg per plant. The seed is edible raw or cooked. The seed oil, flowers and leaves are used medicinally. Plants can be grown as a hedge in exposed positions, tolerating maritime exposure. An essential oil obtained from the flowers is used in perfumery. A gum from the plant is used in the textile industry in calico printing. Leaves are used as goat and sheep fodder. The wood is hard, fine-grained and used for posts, beams, carving, domestic items and makes good fuel. The plant is attractive to bees and is known to be grown as a biomass crop on a 3 year rotation. In Pakistan it is valued as a pollard fuel and fodder crop.
Nitrogen Fixing Potential: This specie is classified by USDA as being a HIGH nitrogen fixer with estimated yields of 160+ lbs/acre or 72>kg/4050m²
Propagation: Establishment and reproduction of Elaeagnus angustifolia is primarily by seed, although some spread by vegetative propagation also occurs. Cold stratification required for 30-60 days.
N.B I’m not sure how the Nitrogen fixing potential of the above species are calculated and the relationship between regular pruning and N input into soils, but it’s something I intend to look into further. If anybody can clarify this matter please comment below.
CAUTION – These are pioneer plants, their ecological role is to take a position in disturbed sites and sites of poor fertility. In doing so they restore soil health and build fertility eventually giving way to more permanent plants. If allowed to seed these plants will quickly colonize disturbed sites such as vast areas of plowed fields that have been extensively cleared of nearly all wildlife to cater for industrial agricultural practices. Because of the tendency of these plants to establish quickly in these areas, they are often referred to, rather ironically, as noxious and invasive species. There may be some examples of these plants displacing healthy native floral communities but not that I have witnessed. It’s advisable to check your local environmental agency to see whether these plants are considered invasive in your area before planting.
Miscanthus x giganteus – Giant Miscanthus
Propagation: The plants can be propagated easily from division and even from small pieces of rhizomes
Planting Material: Rhizomes of these plants can be used and will establish well within a few seasons.
2. Nitrogen Fixing Ground Cover
|White Clover – Trifolium repens under the shade of a Walnut tree in our forest garden four months after sowing.|
A perennial Nitrogen fixing ground cover should be established quickly in the pathways and on the vertical edges of the bed to protect the soil from erosion and provide a further source of Nitrogen input to the polyculture. I have experience using White Clover – Trifolium repens for this purpose but there may be other suitable species.
Sowing the Ground Cover
Following digging out the pathways, slightly loosen the surface of the path with a rake and hand sow the white clover seed onto the surface of the path and into vertical edges of the beds at a rate of 0.75 g per m length of bed. Tamp down with a shovel and water with a fine head sprinkler. The seed should germinate within 5 – 6 days. The best time to sow is late April – mid-June. Keep a close eye on the emerging seedlings and irrigate when below the soil surface is dry. Keep foot traffic to an absolute minimum whilst the cover is establishing.
Maintaining the Nitrogen Fixing Ground Cover
Nitrogen Fixing Ground Cover Species Overview
Trifolium repens -White Clover
|Plants for Pathways – Trifolium repens – White Clover|
Overview: White clover is a dwarf, prostrate, mat-forming perennial that can spread via stems which freely root along the ground at the nodes. Easily grown in average, medium, well-drained soils in full sun to part shade. Prefers moist soils in light shade, but tolerates full sun and moderately dry soils.
Uses: White clover has been described as the most important forage legume of the temperate zones. Besides making an excellent forage crop for livestock, clovers are a valuable survival food: they are high in proteins and although not easy for humans to digest raw, this is easily fixed by boiling the harvested plants for 5–10 minutes. Dried flower heads and seedpods can also be ground up into a nutritious flour and mixed with other foods, or can be steeped into an herbal tea. The plants ability to spreads aggressively by creeping stems makes is a good ground cover plant. The plant is also used as a companion plant when undersown with cereals or tomatoes.
Nitrogen Fixing Potential: The species is classified by USDA as being a HIGH Nitrogen fixer with estimated yields of +160lbs/acre or +72kg/4050m² or 0.018g /m2.
Other sources state up to 545 kg of N per hectare per year is possible.
Biodiversity: The plants provide a source of nectar and pollen for a number of native bees as well as the honey bee.
Propagation: Best propagated by seed. Pre-soak the seed for 12 hours in warm water and then sow in spring in situ. Division is also possible in the spring and autumn.
We supply Trifolium repens – White Clover seed from our plant nursery – Click here for more info.
3. Comfrey Beds
The comfrey beds provide copious amounts of biomass rich in Nitrogen, Phosphorus, Potassium, Calcium and many other valuable plant nutrients that the plants mine deep in the subsoil. The plants can produce 60 cm long roots that harvest these nutrients and relocate them into the plant biomass back on the surface. The biomass is used to feed crops in the garden
|Comfrey Patch Layout|
Planting out the Comfrey Patch
Maintaining the Comfrey Patch
Feeding – After you have cut the comfrey, mow the pathways between the beds and empty the contents to the base of the comfrey plants. Any mowings from the surrounding area can be used in a similar way. As the Nitrogen fixing hedge establishes, they should be trimmed to the required height and shape with the trimmings also applied to the comfrey. This can be done once a year for the first 4 years but biannually as the hedge develops. For extra feed and to increase yields undiluted urine can be applied to the plant at a rate of approx 1L per plant twice per growing season. Urine is an excellent feed for comfrey.Irrigation – Comfrey will produce more biomass if irrigated and in dry climates it’s essential to irrigate. Comfrey plants wilt very fast in hot conditions and will stop photosynthesising at this point.
20 L m2 / week should be more than adequate. The beauty of biological systems are that if they are managed correctly, each year the soil in the beds will improve resulting in less water required and higher yields.
Comfrey Beds Species Overview
Species – Symphytum x uplandicum – Comfrey ‘Bocking 14’
|Permaculture Plant- Comfrey – Symphytum x uplandicum ‘Bocking 14’|
Overview – ‘Bocking 14’ is a hybrid comfrey plant developed in the 1950s by an original ecotrepreneur Lawrence D Hills specifically for its ability to produce tremendous quantities of biomass. Comfrey is adaptable to many soils but prefers moist, fertile soils. Thin soils over rock will give a poor crop, but on light sands and loams, this crop will be productive if adequate nutrients are present. Comfrey productivity is not very sensitive to soil pH, but the highest yields occur on soils with a pH of 6.0 to 7.0. For more on this incredible plant see a previous post Comfrey – Believe The Hype
Uses – The healing properties of this herb are well renowned, making it an essential first aid plant. The beautiful flowers are highly attractive to a wide range of bees including Apis mellifera – the western honey bee. Comfrey has a long history of use as an animal feed. The leaves are best received by animals wilted. Fresh leaves can be eaten by pigs, sheep, and poultry but cattle, rabbits and horses will prefer to consume wilted leaves. Research indicates that a comfrey solution can be used to prevent powdery mildew. Pest predators such as spiders, lacewings and parasitoid wasps associate with this plant. It’s best to leave some plants alone in order to sustain pest predator relationships.
Uses – Mulch – Freshly cut comfrey leaves make good mulch because they’re high in Nitrogen, so they don’t pull nitrogen from the soil while decomposing, as high-carbon mulches like straw and leaves do. Comfrey’s high potassium content makes it especially beneficial for vegetables (such as tomatoes, peppers, and cucumbers), berries, and fruit trees. With adequate feed and watering, we’ve seen yields of 2 – 3 kg of biomass per plant per cut. Plants can be cut up to four times in a year.
|One of our comfrey beds before and after the first cut of 2016.|
Uses – Liquid Fertiliser – What I like to call “Comfert”. Fill a barrel, preferably with a bottom tap and a gauze on the inside (to prevent clogging) about 3/4 full with fresh-cut comfrey and add water to fill the barrel. Cover it, and let it steep for 3 to 6 weeks. The smell from the resulting liquid is far from attractive so approach with caution :) The tea may be used at full strength or diluted by half or more. Don’t apply before heavy rain is forecast as most of the nutrients suspended in the liquid will wash straight through the soil. For the best results apply the feed to your vegetables when they are in most need of the extra fertility. This will be different for each crop, for example, tomatoes are best fed when they are setting fruit and then any time during the fruiting period. Applying comfert before this can be counter-productive and make your plants more susceptible to pest problems. The black slurry at the bottom of the barrel can be dispersed evenly back over the comfrey patch.
Uses – Liquid fertiliser concentrate: “Comfert Plus” can also be made by packing fresh-cut comfrey tops into an old bucket, weighing them down with something heavy, covering tightly, and waiting a few weeks for them to decompose into a black slurry. You can put a hole into the bottom of the bucket and collect the concentrate in another container as it drips out. Dilute this comfrey concentrate about 15 to 1 with water, and use as you would Comfert. You can seal this concentrate in plastic jugs until you are ready to use it.
Propagation – Root cuttings are the only way to propagate ‘Bocking 14’. The cuttings should be grown on in small pots and planted out in the spring as soon as the first leaves emerge.
Planting Material – You can plant out with crown divisions or root cuttings. A crown division is simply putting a spade through the center of a mature comfrey plant and transplanting the divided sections. I divided the crown into quarters and these established very well in the first year. Do not cut the plants in the first year in order to allow a deep root system to develop.
In 2016 we started our comfrey trials measuring the inputs and outputs of a 13 m2 patch of Comfrey. For information on this trial see here.
Just in case you have not heard :) we have revamped the online store and now have excellent Comfrey ‘Bocking 14’ root cuttings and crowns available from The Polyculture Project online store.
|The Polyculture Project Online Store|
Biomass Belt Overview
|Enki- Species List (per 10 m length) based on one comfrey bed|
|Elaeagnaceae||4a – 8b||Shrub||Fertility/Biomass/Polleniser
|Elaeagnaceae||3a – 8b||Shrub||Fertility/Biomass/Polleniser
|10||Miscanthus x giganteus
|Poaceae||4a -9b||Herb||Biomass/Nesting Habitat|
|52||Symphytum x uplandicum
|50 g||Trifolium repens
Biomass Belt Plants
The Biomass Belt in Our Market Garden
Köppen Climate Classification – Dfc borderline Cfb
USDA Hardiness Zone: 5b (conservative) – 7a (risky)
Elevation: 565 m
Average Annual Rainfall: 588.5 mm
Prevailing Wind: NW & NE
Garden Name: Aponia – Polyculture Market Garden
Garden Location on our Project Map – See here
The hedge of fast-growing Nitrogen fixing shrubs is planted into 70 cm wide “no tread” bed rows that run parallel to 1.30 m wide “no tread” bed rows of Comfrey ‘Bocking 14’. In between the beds are 50 cm wide pathways that are sown with a Nitrogen fixing ground cover such as Trifolium repens.
|The biomass belt is located in the red box in the above image of our Polyculture Market Garden.|
The beds run lengthwise west to east with the comfrey beds on the south and the nitrogen-fixing hedge on the north. This is to maximise plant exposure to sunlight. The beds and paths are laid out on contour with the beds elevated around 10 – 15 cm above the surrounding pathways. We irrigate the beds by diverting stream water into the paths and dropping sandbags at various ends to control the level. We can raise the water level in paths to approximately 15 cm resulting in the thorough absorption of water into the bed soil. Water is drawn up towards the surface of the bed via capillary action.
We produced liquid fertilizer from one of the comfrey beds for the first two years with the other bed used for harvesting comfrey root cuttings and we have harvested 1000’s of cuttings from this bed.
The liquid fertilizer provided a great supplemental feed for the plants in our young raised beds. As the garden beds developed overtime, soil conditions improved and the liquid feed was unnecessary. We now use the comfrey biomass to apply directly as mulch to perennial beds in the forest garden for our soft fruiting shrubs and fruit trees.
All in all, we’re pretty happy with how the polyculture has turned out. The area is teeming with wildlife during the growing season, the biomass production from the beds and hedge is high and the maintenance is relatively low. The hedging density could probably be halved although it would take a year or two longer to establish. we have not been irrigating the area for the last two year and Irrigation would certainly boost productivity as I’ve noticed in wet summers the comfrey patch is much more vigorous. we’ll see in the coming years how the hedge matures and perhaps one concern may be that more trimming of the hedge facing the path may be required for ease of access.
Here you can see how the polyculture has developed over the years.