Comfrey, nettles and yarrow are herbs that are dynamic accumulators, plants capable of concentrating nutrients at much higher levels than the surrounding soil.
When added to compost, these herbs break down, releasing their concentrated nutrients, helping initiate the composting process in a new compost pile, or restarting it in an existing pile that has slowed right down. This makes them excellent for use as compost activators, also known as compost accelerators or compost starters.
To get a compost heap going, we can add nitrogen-rich materials into its core, such as these herbs, or materials such as manure and urine. This will quickly heat up a cool compost pile and speed up the decomposition process.
Comfrey (Symphytum officinale) is a perennial groundcover herb from the Boraginaceae (borage) family that is native to Europe. It grows up to 80cm in height, and dies down to the ground in winter and re-emerges in spring. It spreads by creeping underground rhizomes.
This is a very useful plant, it’s leaves can be used as a compost starter, and to make fertiliser. It’s often planted along chicken runs as a forage plant, the leaves are very high in protein, and contain vitamins A, C, E and several B vitamins, even B12!
Comfrey is traditionally used as a medicinal herb for external use, and as is commonly used as a chicken forage that plant grown along chicken runs. In farming it’s used as a nutrient trap on slopes at the edges of properties. The deep tap roots can mine nutrients that other plants cannot reach, and bring them back to the surface when their leaves die back in winter, making the nutrients accessible to other plants, and preventing nutrient loss from the site.
The flowers of comfrey plants attract beneficial pollinators such as bees.
The leaves are rich in the major macronutrients, nitrogen, phosphorus and potassium, and can be used to make a liquid fertilizer, known as ‘comfrey tea‘. To make comfrey liquid fertiliser, fill a bucket two-thirds full of comfrey leaves, and add water till it covers all the leaves. Cover the top loosely, and allow the leaves to soak for at least one week, till it turns into a brown stinky liquid that look and smells like liquid manure, and works just as great in the garden!
Nettles, also known as stinging nettles are in fact two different species:
- Urtica dioica is a perennial herbaceous clump forming plant which propagates mainly by rhizomes but to some extent by seeds, growing to 1.5m in height.
- Urtica urens is an annual herbaceous plant growing a single stem, which reproduces exclusively by seeds, and reaches a height of 60cm.
These plants unsurprisigly belong to the Urticaceae (nettle) family, and are found growing nearly worldwide.
To say that nettles are useful plants is almost an understatement!
Nettles are very high in nitrogen, making them ideal for use as a compost starter. They can also be used to make a liquid fertiliser, in the same way as comfrey.
They are extremely nutritious, even considered ‘superfoods’, as nettles are reputed to have a higher nutrient content than any cultivated vegetable or herb. Nettles taste like spinach when cooked, and lose their stinging quality. They’re used in soups, or steamed and used just like spinach. An easy way to prepare nettles is to pick young shoots, soak them in warm water to remove any dirt and debris, place them in salted boiling water using kitchen tongs, boil them for five minutes, then serve them as a vegetable, or add them into soups.
Nettle are a traditional herbal medicine and the leaves can be used dry or fresh to make a soothing herbal tea.
It doesn’t end there though. Nettle stems contain coarse fibres that were traditionally used for the same purposes as linen, and also for making cordage (string). The leaves can be used to make a yellowish green dye, and the roots a yellow dye.
Nettles are also useful companion plants, being more attractive to aphid pest insects than other plants in the garden, they act as trap crops, sacrificial plants that draw the pest to themselves, saving other plants. Since they draw all the aphids in one place, ladybirds lay their eggs under nettle leaves because their larvae voraciously consume aphids!
Don’t rip out all nettles like some gardeners do, as they serve as important host plants (food source) for certain native butterflies, such as the red admiral butterfly in the US, and the Australian admiral butterly in its namesake country.
Yarrow (Achillea millefolium) is a perennial groundcover herb from the Asteraceae (daisy) family that is native to Europe and Asia.
Its small white flowers attract beneficial insects such as ladybirds, lacewings, hoverflies and parasitic wasps which control pests insects in the garden, making it an excellent companion plant.
This interesting plant is reputed to increase the aromatic oil concentration of herbs when grown near them, and therefore their flavour. Some birds use yarrow to line their nests, as it has been found to repels parasites. It’s also used traditionally as a herbal medicine. The leaves are also used for making a yellow dye.
Yarrow plants have fine, ferny leaves, and weak stems, so by mid to late summer, after flowering, they can get quite straggly, and are usually cut back in height. Their prunings, along with those of other plants that need tidying at the end of summer, can be put into the compost to promote the composting process.
How to Use Compost Activators
To use comfrey, nettles or yarrow as compost activators:
- Make a hole at the top of the compost pile, deep enough to reach into its centre.
- Place a handful (or more) of leaves into the hole.
- Close up the hole to cover the leaves.
- Lightly water the compost pile so it’s just barely moist, as the composting process requires some moisture to work.
- Leave the compost pile alone for a few days to allow the composting bacteria to do their work, and get the composting process going.