The benefits of making Comfrey tea (liquid fertiliser)

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I must admit, the first time I heard the phrase ‘Comfrey tea’ I half expected it to be some kind of trendy new herbal tea option from Twinings, however clearly the idea isn’t for us to drink the stinky stuff but for our beloved plants to enjoy an invigorating boost – from flowers to vegetables.

Plants all benefit from a top-up with a liquid feed as they progress through the growing season, many soils and composts will become depleted of the key vital ingredients of Nitrogen (N), Phosphorous (P), Potassium (K) after 6-8 weeks. Even if a plant doesn’t seem to be suffering, it certainly won’t say no to a fertiliser tea pick me up and you may be rewarded with additional blooms or fruit. You’ll also help to avoid diseases because stronger plants will be more resistant.

Making Comfrey tea or any other liquid fertiliser is an ‘absolute doddle’, you don’t have to buy it; the ingredients are mostly available to you free of charge and it will even make you a lover of some weeds like nettles and horsehair. In the photo gallery below I have made myself some Comfrey and Nettle tea. I make rather a lot, since I use it at my allotment where a water butt 1/3 full is necessary, eventually I bottle it up using old plastic orange juice bottles because it’s easier to dilute and frees the water butt for additional brews I might be planning throughout the growing season. However, there’s nothing to stop you using a bucket to create a small quantity (you’ll actually have the added benefit of a much smaller ‘sewage stink’… boy does Comfrey tea smell when it’s brewing!).

Step by Step: Making Comfrey Tea

  1. Find some Comfrey (bees love it, I dug up a root and planted it near my compost bins).
  2. Using gloves gather a bin liner full of leaves and stems (can be prickly).
  3. Place the leaves into your container (water butt / bucket).
  4. Add ‘anything else’ (see N.P.K. Composition table below).
  5. Squash and chop repeatedly with a metal spade.
  6. Add some weight / bricks (I place my bricks in a wire cage – easier to remove for stirring).
  7. Add enough water to cover the vegetation by at least 2 inches.
  8. Cover to keep flies out (really? oh yes…).
  9. Stir well at least weekly to oxygenate (peg on your nose).
  10. Keep stirring and wait 3-4 weeks (weather/heat dependent).

Once the 3-4 weeks are up you can add the liquid fertiliser to your watering can at a ratio of around one part to 20 parts water. Don’t be tempted to ‘over feed’ your precious plants... like naughty grandparents buying sweets for their grandchildren every day it might make you feel better but its not better for the children (or plants)! Overfeeding can actually have the opposite effect.

What about these ‘other ingredients’?
A liquid fertiliser tea can be made from more than just Comfrey (although Comfrey is amazing stuff, containing vitamin B12, magnesium and essential Calcium), I sometimes add nettles to the mix, especially early on in the season when I’m seeking a high Nitrogen (N) fix to boost leaf growth. The exact choice of what you put in your home brewed liquid fertiliser depends a lot upon what you’re feeding it to and for what purpose.

The table below features a list of key compost ingredients with their respective NPK values, you may well note that Horse Manure – whilst being a popular choice for gardeners and allotmenteers alike is actually a pretty poor all-round compost. Personally I’m going to encourage the children to get some pet rabbits!

Compost Type N% P% K%
Pigeon Manure 4.19 2.24 1
Rabbit Manure 2.4 1.4 0.6
Coffee Grounds 1.99 0.36 0.67
Comfrey 1.8 0.5 5.3
Nettles 1.7 0.6 4.3
Seaweed 0.0 0.0 1.0
Chicken Manure 1.63 1.54 0.85
Ground Eggshells 1.19 0.38 0.14
Horse Manure 0.44 0.35 0.30
Banana Skins 0 3 41.76
Orange Skins 0 3 27
Bone Meal 3 15 0
Tomorite *Fert 4 3 8
Vitax Q4 *Fert 5.3 7.5 10

 

A practical example: Giant Pumpkins

  • I am rather obsessed with growing giant pumpkins; at the start of the season as well as a good base of manure, seaweed etc. I like to give them a liquid fertiliser tea – and initially I want the vines to grow quickly – I want a high Nitrogen (N) mix. I will usually give the plants a nettle tea only.
  • After a few weeks I also want lots of flowers, a healthy plant and plenty of female fruiting options for pollination – so I need a high phosphorous (P) feed – I’ll make a chicken manure tea using some fertiliser pellets and switch that.
  • Late in the season, as the plants put on fruit, if I don’t want them to fall off or fail due to mineral deficiency or weather conditions, and I want my pumpkins to be BIG, so I need a feed that is higher in Potassium (K), this is where Comfrey and Banana skins are excellent ingredients for a compost tea.

Of course in reality I realise that a three stage liquid fertiliser strategy is extreme (giant pumpkins are extreme…), most people just use nettles and/or Comfrey, they have good all round N.P.K. ingredients and that keeps life simple. Surprisingly even the most dreaded of Jurassic weeds the Horsehair has compost tea value – it is high in silica and is a useful fungicide against mildew, some rust and blackspot (yes horsehair / marestail – so maybe now you’ll learn to love it).

So that’s Comfrey tea making in a nutshell, may this advice be helpful and may the NPK composition table above make you rethink the type of liquid fertiliser you make AND when to do so. I also strongly advise the addition of a seaweed fertiliser – not for NPK values (as Seaweed is low on these) but for micro-nutrients; see my post ‘Seaweed – too many benefits to be ignored by plant growers‘ to become a seaweed convert.

 

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About Author

Matt Peskett is GrowLikeGrandad (if you want to know why read 'About the Editor). He has a 'heavy clay' allotment and is a member of the Dorking Allotment Holders Association (DAHA). Matt also has a medium sized 'sandy soil' hillside garden (Italian terrace designed) and enjoys photography - especially nature. Matt takes inspiration from gardens like Hidcote, Great Dixter and Sissinghurst and enjoys watching anything on TV with Monty Don in it.

1 Comment

  1. Hi Matt, do you know how old plants need to be before you start harvesting leaves? I planted half a dozen bare rooted plants last year but not sure if I should wait another year before attempting a ‘brew’.

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