Comfrey liquid feed is one of the most effective organic fertilisers available to a home grower, and it costs nothing once you have a comfrey plant established. It is naturally high in potassium, the nutrient that fruiting plants need most when they are flowering and setting fruit, and it can be harvested and brewed repeatedly throughout the growing season.
Why comfrey?
Comfrey (Symphytum officinale) has unusually deep roots that draw up nutrients from well below the surface, nutrients that most vegetable plants cannot reach. Its leaves are exceptionally rich in potassium, and contain useful amounts of nitrogen and phosphorus too. When steeped in water, those nutrients leach out into a liquid that plants can absorb quickly.
The variety to look for is ‘Bocking 14’. It is a sterile hybrid that will not self-seed and spread, and it produces more leaf growth than wild comfrey. Plant it once in an out-of-the-way corner of the garden and it will supply feed for years with almost no care.
What you need
- A large container with a lid, a bucket, barrel, or old dustbin all work well
- A brick or heavy stone to weigh the leaves down
- Fresh comfrey leaves (cut when the plant is growing vigorously, before it flowers)
- Water
- A watering can for applying the finished feed
How to make it
- Cut a good armful of comfrey leaves and pack them tightly into your container.
- Place a brick or heavy stone on top to keep the leaves pressed down and submerged.
- Fill the container with water so the leaves are fully covered.
- Put the lid on, the liquid will smell strongly as it ferments, so keep it sealed.
- Leave for three to four weeks. The liquid will turn a dark brown colour.
- To use, dilute one part feed to ten parts water, it should look like weak tea.
How to use it
Apply the diluted feed at the base of plants, not over the leaves. Start once the first flowers or small fruits appear, and repeat every 7–10 days throughout the growing season.
Comfrey feed is particularly well suited to:
- Tomatoes
- Courgettes and marrows
- Runner beans and French beans
- Peppers and chillies
- Cucumbers
- Strawberries
A note on the smell
Comfrey feed smells, quite strongly, especially after a few weeks of fermenting. This is completely normal and is a sign that the nutrients are releasing properly. Keep the lid on at all times and store the container away from doors and windows. The smell disappears once diluted for use.
Nettle tea: a free alternative
If you cannot source comfrey, stinging nettles work on the same principle and grow freely across most of England. Pack freshly cut nettles into a container of water, leave for two to three weeks, and dilute in the same way before applying.
Nettle feed is higher in nitrogen than comfrey, which makes it especially useful for leafy crops like lettuce, kale, and spinach. It also benefits fruiting plants, particularly early in the season when they are building leafy growth before they start to flower.
For the best of both, steep comfrey and nettles together in the same container to produce a balanced feed with both high potassium and nitrogen.