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Vegetable Garden

How to Make Comfrey and Stinging Nettle Fertilizers

April 30, 2012
How to make comfrey or nettle fertiliser

Comfrey Plant


Used for centuries before chemical fertilizers became popular, homemade comfrey or nettle ‘teas’ are easy, quick-release fertilizers that you can easily make at home and will save you money as you avoid buying artificially created variations.

When to use fertilizers

If you keep the soil fertile by adding lots of bulky organic matter (well-rotted manure, compost, leaf-mold) you shouldn’t have to worry about adding additional fertilizers too much.  However, there are certain circumstances when it’s helpful:

  • To raise nutrient levels in a poor or new soil.
  • To get higher yields from hungry crops such as potatoes, cabbages & squashes.
  • In containers where the nutrients in compost are used up quickly.
  • Top dressings of fertilizer can be added once the plants have established.
  • As an instant plant ‘pick-me-up’ sprayed on as foliar feeds.

Comfrey ‘Tea’

Rich in potash (potassium or K – great for flowering), comfrey also contains high levels of Nitrogen (N) for leaves (N3:P0:K10).  The variety Bocking 14 is the best one to plant in a garden as it’s less invasive. Comfrey can be difficult to get hold of in Ireland and is usually obtained by asking fellow gardeners, though you may find it in local markets (I’ve been reliably informed there’s a market stall in Kilkenny Farmers Market that often sells it). The Organic Centre sometimes stock root cuttings and in the UK it’s available online from The Organic Gardening Catalogue.

Wilted comfrey leaves can be placed around plants as a mulch or used as a liner in potato and tomato trenches – make a trench, add the leaves, cover with a sprinkling of compost then plant on tip of them. They can also be added to compost heaps (but only in small batches as they can go slimy). Be careful not to add any roots or flower heads or you may have comfrey popping up where you don’t want it.

A rich comfrey brew is made by packing leaves into an old dustbin, about half way up, then placing a board on top, weighed down and a lid added. A hole can be drilled in the bottom of the bin and a jar placed under to catch the drips or a tap added. The resulting liquid should be diluted 10 – 20 times with water before use.  Avoid getting it on your skin. Alternatively infuse around 3kg of fresh comfrey leaves with 45 litres of water and leave to stand for a month. This tea can be added undiluted to containers or plants for a pick me up.

How to make comfrey or nettle fertiliserStinging Nettle ‘Tea’

Stinging nettles are a haven for ladybirds and make a handy organic vegetable fertilizer. They are lower in potassium than comfrey but much easier to come by and contain an average N2:P0:K5 but with high trace elements. Young stinging nettle leaves are cut in the spring (wearing a thick pair of gloves!) and made the same way as comfrey tea. A quick method is to add 1kg of nettles to 20 litres of water.  Use the liquid undiluted when it starts to smell, usually a couple of weeks.

Alternatively, organic gardening guru Joy Larkcom recommends wrapping some nettles up in a sheet of muslin or old net curtain, then tying and hanging them in your water-butt.  Change the bag often as the leaves break down so that the feed doesn’t become too strong.

Have you used homemade fertilizers in your garden? How did you find them?