Monday 9 October 2017

How much Comfrey can you grow on 13 m2 ? Comfrey Trial Results Year 2 - 2017

Inspired by the work of Lawrence D Hills (1911–1991), who undertook extensive research on comfrey during his lifetime, we decided to start a comfrey trial of our own. Hills discovered a strain of comfrey that produced very high quantities of biomass -  Symphytum x uplandicum 'Bocking 14'. Using this plant we set up a trial bed in order to discover:
  • how much biomass we can produce in our climate 
  • how well comfrey can fertilise our crops
  • how attractive comfrey is to garden wildlife
  • whether growing comfrey has a beneficial impact on the soil

Our Comfrey Trial Beds

If you would like to learn more about comfrey and why it's considered such a great plant by many people take a look at our previous post Comfrey - BELIEVE the HYPE!.

Below you will find an overview of our trial and the results from 2016 and 2017.

The Comfrey Trials 

Comfrey Patch Overview 

The comfrey beds are located in the red box in the above image of our Polyculture Market Garden in Shipka, Bulgaria

Location - Our Market Garden, Shipka, Bulgaria
Climate: Continental Temperate
Latitude: 42°
Elevation: 565 m
Average Annual Rainfall: 588.5 mm
Co-ordinates: 42.71259, 25.32575

Species/Cultivar - Symphytum x uplandicum 'Bocking 14'
Test Bed Area - 13 m2
Bed Dimensions - 10 m x 1.3 m 
Total Plants - 42
Approx. planting spacing - 60-70 cm


The patch was prepared in the spring of 2015. Two 13m2 beds are allocated to the comfrey, but only 1 bed is used to take records. For instructions how to set up a comfrey patch see our previous article here

Graphical Representation of the Comfrey Trial Patch

We started by taking a base soil sample, after which we dug over the plot, removing weeds and adding 20 L of mature compost per m length of bed (200L) and 70g of wood ash per m length (700g). We planted out the beds using divided crowns of larger plants and left them to grow without disturbance for the entire season of 2015. We also broadcast approx. 1.5 g per m2 of Trifolium repens - White Clover  onto the pathways in between the beds.

Planting Material - It's easy to plant out with crown divisions or root cuttings in the spring when the soil has warmed. A crown division can be obtained from simply putting a spade through the center of a mature comfrey plant and transplanting the divided sections. For our patch I divided 2 yr old plants into quarters, sometimes sixths, and these established very well in the first year. We did not harvest the leaf biomass in the first year in order to allow a deep root system to develop. However, if you use large divisions you can start harvesting in July.

Plants in the 2nd month after planting in 2015

Trial Management  

Irrigating - Irrigation is applied to the beds every 10-14 days without rain. We use flood irrigation diverted into the paths from mountain stream. I'd estimate 30 L per m length each week without rainfall would be sufficient for good growth rates.

Kata and Ute cutting the patch
Cutting -  We cut the Comfrey four or five times per season (see below for dates and weights). The comfrey is cut to approx 5 cm from the ground using a sickle, shaken out so all of the wildlife drops out and weighed immediately.

We generally leave the plants to flower for 7 -10 days before the first two cuts, seeing as the bees are so into the flowers.

Comfrey 'Bocking 14' before the first cut in April

Kata, Natasha and Ute cutting and weighing 

Mowing - 
After the cut, the pathways and surrounding paths are mown and the trimmings are applied more or less evenly to the surface of the bed.

Comfrey Patch - before and after cut and path mowing 

Regrowth 23 days after the first cut 

Usage - Preparing liquid fertiliser (Comfert) - In 2016 we used the cuttings to make liquid fertiliser. We place the fresh material into a 200 L barrel with stones on the top to compress the material and leave it to decompose for a few weeks. The result is a black smelly slurry that can be sieved off to leave a quantity of dark brown liquid. The liquid can then be diluted from 1-15 to 1-20 and applied to crops. The largest cut we made from 13m2 bed just about fit into the 200 L barrel.

Usage  - Mulch - We did not make comfert in 2017, instead we used the comfrey leaves directly as mulch. I estimate that approx. 8 kg of fresh material can provide a good mulch for 1.5 m2 of ground.

Just under 8 kg of comfrey biomass covers 1.5 m2 bed with a 10-15 cm deep layer 

Fertilizing  - The initial input of 20 L of mature compost per m length of bed and 70g of wood ash per m length was applied when we established the bed in the spring of 2015. In 2016 and 2017 the only fertility inputs were the trimmings from the pathways between and around the garden beds.  We mowed this section after each cut and each time emptied approx four 30 L mower bags of trimmings onto the comfrey beds

During the season we casually observed invertebrate activity in the patch and took note of wild plants that establish in the beds.

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The Results - 2016 & 2017

How Comfrey Affects the Soil 

As well as how much biomass we can harvest we are also interested to learn how comfrey effects soil fertility and as such have been gathering soil samples from the plot for analysis.

We took a soil sample in the area before preparing the beds in March 2015, a sample in November of 2016 after the first season of cuts were made. and from then on we sample in March and November each year. All samples are sent to NAAS of the Ministry of Agriculture and Food.

 The results of the soil analysis can seen below (November results will be added soon)

Soil Results 


  • For higher yields the plants can be cut before flowering. We did not carry out this practice to  allow the bees to forage.  
Carpenter Bees one of many species of solitary bees that feed from the Comfrey flowers as well as Honey bees.

    • A simple way to increase yields is by applying a urine fertiliser and we hope to experiment with this in the future. 
    • We use most of the comfrey in the market garden for mulch and for making compost. Comfrey can also be used to feed animals. Our rabbits and pigs both enjoy the fresh material, and we use plants growing in our garden around the animal housing for this.  

    Our pigs enjoying the Comfrey leaves

    Joining the Trials 

    If you would like to join the comfrey trials fill in your details below and we'll email you our record keeping templates. It will be great to have records from all over the world and see how well these plants grow in different climates.

    Buying Comfrey

     Root cuttings and crowns come from our bio nursery and are  100% biologically grown - Click here for crowns and here for cuttings. 

    20 Root Cuttings - €32 
    50 Root Cuttings - €65 
    100 Root Cuttings - €120 
    500 Root Cuttings - €500 
    1000 Root Cuttings - €930 

    Price includes delivery via international courier service, recorded and tracked. Estimated delivery time is 5-9 days

    Comfrey Crowns -  €3 per crown + delivery 

    Crowns emerging in early spring 

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