Comfrey and Nettle Tea: Homemade Liquid Fertilizers From Weeds

Two common plants make some of the best homemade liquid fertilizers there are. Comfrey, a deep-rooted perennial, has leaves rich in potassium, which fruiting crops like tomatoes need. Stinging nettle, a weed many gardeners already have, is rich in nitrogen, which drives leafy growth. Both can be turned into a liquid feed in a bucket with nothing more than water and time.

These "weed teas" are a way to recycle nutrients from plants that grow freely, rather than buying bottled fertilizer. They do have one drawback: they smell strongly. With a lid and a sensible location, that is easy to manage.

Comfrey vs nettle at a glance

	Comfrey	Stinging nettle
Main nutrient	Potassium (also some nitrogen)	Nitrogen (also iron, magnesium)
Best for	Tomatoes, peppers, squash, beans, flowers, fruit bushes	Leafy greens, cabbage family, young plants, lawns
When to use	From flowering through fruiting	Early in the season, during leafy growth
Harvest	Cut leaves 3–5 times a year	Young tops in spring, before flowering
Smell	Very strong	Strong

Many gardeners use both: nettle in spring to build plants, comfrey from midsummer to feed fruit.

Growing and harvesting comfrey

The variety most gardeners grow is Russian comfrey 'Bocking 14', a sterile hybrid that does not spread by seed. Ordinary comfrey can seed itself around the garden, so choose 'Bocking 14' if you are planting it fresh.

Comfrey is very hard to remove once established, because any piece of root left in the ground regrows. Plant it in a permanent spot at the edge of the garden.

Cut leaves about 5 centimeters above the ground when the plant is about 60 centimeters tall. It regrows quickly, and you can usually cut three to five times a season. Wear gloves, since the leaves are covered in bristly hairs that irritate skin.

Harvesting nettles

Pick young nettle tops in spring, before the plants flower, when they are most tender and nutrient-rich. Always wear thick gloves and long sleeves. Leave some nettles standing: they are important food plants for the caterpillars of several butterflies.

Avoid nettles growing beside busy roads or in areas that may have been sprayed with herbicides.

How to make the tea

The method is the same for both plants.

Chop the leaves roughly with shears. Smaller pieces break down faster.
Pack a bucket about half full with leaves.
Add water until the leaves are covered, roughly 1 kilogram of leaves to 10 liters of water. Rainwater is ideal.
Weigh the leaves down with a brick or stone so they stay submerged.
Cover with a tight lid and place the bucket somewhere away from the house and seating areas.
Stir once a week if you can bear the smell.
Wait: nettle tea is ready in about two weeks, comfrey tea in three to five weeks. The liquid turns dark brown and the leaves break down into sludge.
Strain the liquid through an old cloth or sieve into bottles or a watering can. Add the leftover sludge to the compost pile.

Steps for making a weed tea — Chop, soak, weigh down, wait, strain and dilute.

A smell-free alternative for comfrey: concentrate

Instead of soaking in water, you can make a concentrate:

Pack comfrey leaves tightly into a container with a small hole or tap at the bottom, such as an old drainpipe with a cap or a bucket with a tap.
Weigh them down firmly and cover with a lid. Do not add water.
Over two to three weeks, a dark, thick liquid drips out as the leaves decompose.

This concentrate smells far less than the water version and keeps for months in a sealed bottle in a cool, dark place. Dilute it more strongly, about 1 part concentrate to 15 to 20 parts water.

How to dilute and use

Weed teas are strong and should always be diluted before use.

Feed	Dilution	How often
Comfrey tea (water method)	1 part tea to 10 parts water	Weekly once fruiting crops start flowering
Comfrey concentrate	1 part to 15–20 parts water	Weekly from flowering
Nettle tea	1 part tea to 10 parts water	Every 1–2 weeks during leafy growth
Seedlings (either)	1 part to 20 parts water	Every 2 weeks

Water the soil around the base of plants. Apply to moist soil rather than bone-dry soil. Stop feeding edible crops a couple of weeks before harvest, and avoid splashing leaves of crops eaten raw.

Other uses for comfrey leaves

Mulch: lay fresh leaves around potatoes, tomatoes or currant bushes. They wilt and break down quickly, releasing nutrients into the soil.
Planting holes: put a handful of chopped leaves at the bottom of the hole when planting potatoes or tomatoes.
Compost activator: comfrey leaves heat up a compost pile and add potassium.
Potting mix: well-rotted comfrey leaf mold, mixed with leaf mold, makes a rich homemade potting compost.

Safety notes

Comfrey contains compounds that are toxic to the liver when eaten. Do not eat it or make it into herbal remedies to take internally. Use it only as a garden fertilizer.
Wear gloves when handling both plants.
Label bottles of tea and concentrate clearly and keep them away from children and pets.

Will it replace other fertilizers?

For most home vegetable gardens, a combination of compost in the soil and weed teas during the growing season covers the main nutrient needs. Weed teas are not as precisely balanced as commercial products, so if plants show persistent signs of deficiency, a soil test is worth doing.

For a gentler, more general feed, try brewing finished compost instead with our compost tea guide.