Garden DIY: How to make compost tea and boost your garden's health

A liquid fertiliser made of comfrey will give your vege patch a boost.
Melissa Adams MLA

A liquid fertiliser made of comfrey will give your vege patch a boost.

As most gardeners know, weeds tend towards the vigorous end of the plant health spectrum. 

But that means weeds can actually be good for your garden. Many have with deep tap roots, like dandelions, to allow them to draw valuable minerals and nutrients from the soil and store it in their roots and leaves. That makes these plants mineral powerhouses. If you steep them in water those valuable nutrients are released, and you'll create a rich tonic that will give your vege plot a boost.

While you can use pretty much any plant or weed to make a liquid fertiliser, consider different plants based on the nutrients they mine. For example, clover harvests nitrogen; dock accumulates calcium, potassium, phosphorus and iron; sorrel takes up phosphorus; chickweed absorbs potassium, phosphorus and manganese; and dandelions absorb a host of minerals.

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Whatever herb or mix of herbs you're using to make your plant tonic, harvest enough leaves to fill a 10-litre bucket or similar-sized container with a lid, packing the herbs in. Fill it up with water, cover and steep for 2-3 weeks until the leaves decompose (the hotter the weather, the less time it will take), stirring occasionally. Stirring mixes oxygen into the liquid, which is essential to the survival of the bacteria breaking down the plants. The mixture will bubble indicating that it's fermenting. When it stops bubbling, strain and use at a ratio of 1 part tea, 10 parts water.

Stinging nettle tea
Nettles might be classed as a weed, but the perennial nettle, Urtica dioica, is also a superfood! It has many therapeutic properties, is full of fibre and contains many vitamins and minerals, including calcium, potassium, iron, magnesium, manganese, silica, silicon, copper, zinc and phosphorus, plus vitamins A, C, D, E and K, and B complex vitamins. If you can avoid the sting (plunge the nettles in boiling water for a few seconds and the sting disappears), nettles are a tasty, extremely nutritious food (the taste is described as somewhere between spinach, cabbage and broccoli).

Those same nutrients are beneficial to the garden and you can deliver them in the form of a nourishing, nitrogen-rich tea for your plants. Urtica urens, an annual nettle, can also be used as a plant tonic, though it's not eaten or used for medicinal purposes.

Just be aware that Urtica dioica is a pest plant in some areas and banned from sale or propagation. Check with your local council for details.

Nettles like soils high in nitrogen, so you'll find them growing in areas that are well manured. When harvesting, wear gloves and long trousers to protect yourself.

German chamomile antifungal tonic
Planted in the garden, German chamomile (Matricaria recutita) draws potassium, sulphur and calcium to the soil's surface. It was historically referred to as "the plant's physician" due to the belief that it "healed" ailing plants when it was planted beside them.

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Chamomile has been proven to have antifungal properties, so a chamomile tea is a superb natural remedy for plants suffering from mildew or any other fungal diseases.

Use it for seedlings too, to prevent damping off. To make a tea, pour 2 cups of freshly boiled water over ¼ cup chamomile flowers. Let it steep until cool, then strain. Water your seedlings or spray it onto plants.

Comfrey fertiliser
Comfrey (Symphytum officinale) absorbs large amounts of potassium from the soil, making it a useful fertiliser where high levels of this mineral are needed. Any plant that bears fruit will welcome a dose of comfrey tea. You need to keep comfrey in check, as it seeds widely and so can get rather weedy.

If you can find it, Russian comfrey (Symphytum x Uplandicum) is sterile (you propagate it by root division) so it makes an excellent mulch under fruit trees. Otherwise grow comfrey in large, deep containers, or in a contained part of the garden.

If you are using comfrey as a herbal tea for the garden, you should be able to get four or five good harvests from late spring to late autumn. Freshly harvested leaves can be used as a mulch too, which will break down and release nutrients into the soil.

Or place one- or two-day-old wilted comfrey leaves in the bottom of trenches before planting your spuds.

 - NZ Gardener


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