Make your own comfrey fertiliser

Updated August 2023

At this time of the summer your greenhouse plants may be growing a lot, and maybe you have already harvested your first tomatoes, cucumbers and other fruits and vegetables in the greenhouse. To promote the growth of plants and the production of fruit, your plants will need some extra nutrients.

The comfrey plant is a great fertilizer as it contains high levels of nitrogen, phosphorus and potassium, which help the growth and make the roots strong as well as increasing the production of flowers and fruits. You will get healthier greenhouse plants and a better harvest. Especially your cucumber plants and tomato plants will thank you.

In spring you can swap out comfrey with for example stinging nettles, which you can find in nature. Nettles contain high levels of nitrogen and are a good substitute for fertilizer in spring when your plants are growing.

 

What you’ll need:

• A large bucket (not metal)
• Garden shears
• Comfrey (earlier in the year you can also use nettles before they have flowered)
• Rainwater (tap water can also be used)

If you do not have comfrey in your garden, your neighbour may have it, or you can look for it near fields or roadsides.

 

How to make your own fertiliser:

1. Use a bucket and fill it with comfrey leaves and stalks (avoid comfrey seeds unless you want comfrey plants all over the garden).
2. Use your garden shears and cut leaves and stalks into smaller pieces (see the picture above).
3. Put the bucket with comfrey somewhere in the garden with sunlight. The fermentation process creates a strong odor so you may want to put it someplace where you are not bothered by the smell.
4. Add rainwater so the comfrey is completely covered and let it steep in approx. three weeks until the leaves are dissolved. Stir the liquid fertilizer regularly – preferably once a day or at least five times a week.
5. You can strain your home-made fertiliser and pour it into bottles. What is left can be added to the compost. Alternatively, you can leave the fertiliser in the bucket and take it directly from the container when you need it.
6. Keep the comfrey fertiliser somewhere dark and cool, so it lasts longer.
7. Dilute the comfrey fertiliser 1:10 (or for young plants 1:20) and irrigate your greenhouse plants with your home-made fertiliser. Avoid pouring the fertiliser on the leaves and plants directly, but instead irrigate the soil.

 

If you have comfrey left over, you can use some of the leaves as groundcover in the greenhouse which will provide nutrition for your plants. Save this recipe for later and try to also use nettles instead of comfrey next spring.