Natural liquid nettle feed is superb for keeping your plants healthy – it just smells terrible

Long before modern pharmaceutical companies did their best to persuade us to rely on a battery of synthetic chemicals to treat pests and diseases, gardeners used a wide variety of planet-friendly methods to keep our plants hale and hearty, utilising natural materials found close to hand. Great for plant and soil health and kind to the environment. They’re also cheap and easy to make.

A liquid foliar feed, for example, made from chopped-up young nettle leaves (Urtica dioica) and fermented in a lidded bucket of water for 2-4 weeks is a brilliant and wonderfully cost-effective way to boost healthy growth in early summer. It has a near-miraculous effect on any young transplants (hello dahlias) or herbaceous perennials being badly damaged by slugs and snails, helping them fight off attack and quickly outgrow the damage.

Not only is this nutritious, health-boosting liquid rich in nitrogen, the nutrient required for leafy growth, liquid nettle feed, or tea as it’s known, contains lots of trace elements beneficial to plant health including copper, zinc, calcium, iron, boron, sulphur and magnesium as well as chlorophyll, silicic acid, antioxidants and phenolic compounds. Just make sure to strain it and dilute it down to the colour of weak tea before use, applying it generously to the leaves of the plants using a watering can fitted with a fine “rose”.

The only downside is its formidable pong, which can cling stubbornly to skin and clothing even after being diluted. To avoid being treated as a social pariah, make sure to wear protective clothing when you’re preparing and applying it. The same advice goes as regards collecting its young leaves, which can deliver painful stings when in contact with bare skin.

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Our native nettle is just one of several hardy, vigorous perennials whose leaves can be used as a natural biostimulant to boost soil and plant health. Another is comfrey or Symphytum officinal, also commonly known as bruisewort, knot bone, Saracen’s root and here in Ireland as Lus na gCnámh mBriste. Such is its long history of medical and horticultural use that Lawrence Hills, the inspirational organic gardener and founder of the international association now known simply as Garden Organic, referred to it as “a natural mineral mine”.

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Hills researched the nurturing powers of comfrey in depth, eventually writing a book on the subject as well as introducing into cultivation the outstanding sterile variety that organic gardeners now know as Symphytum x uplandicum ‘Bocking 14′. Just as for nettle tea, the fresh young leaves are sheared off the plant and then squeezed into a lidded bucket where they’re covered in water and then left to stew. Alternatively, you can use an upturned plastic drinks bottle (lid intact), with its base cut off. Press the chopped leaves down into the upturned open base before covering with a plastic bag sealed with an elastic band. Every couple of weeks you can remove the bottle lid and drain off the almost tarry liquid to use as a feed, making sure to dilute it with water to the colour of weak tea. Then top up the top of the bottle with fresh leaves to keep the process going.

Unfortunately the pong of comfrey tea is every bit as bad as nettle tea, but the benefits to plant health and vigour are every bit as notable. Comfrey is especially high in potassium, the major plant nutrient essential for good flowering and fruiting, so this is a great feed to use on summer bedding displays or food crops such as tomatoes, beans and peas. Because it’s such a vigorous, fast-growing, persistent plant, make sure to grow it in a tub or in a garden area where it won’t compete with less vigorous species.

A native perennial that most gardeners regard as a stubborn weed, field horsetail or Equisetum arvense is another plant known for its ability to mine the soil for precious nutrients. Used as a liquid plant feed, it has anti-fungal and antibacterial properties, which is why it’s traditionally used to help fortify potato plants against the risk of blight. In biodynamic gardening it’s also used as a foliar feed and soil drench to help control other common pests and plant diseases.

To make equisetum tea, simmer a bowlful of field horsetail stems in hot water for about 20 minutes and leave it to cool, before straining off the liquid and bottling it. Used in diluted form, it can be applied as a fortnightly foliar feed or root drench. It’s not our only native weed that’s rich in plant nutrients. Other examples include dandelion, whose leaves are rich in iron; scutch grass whose leaves are rich in potassium; and ground elder, which is rich in nitrogen, potassium, phosphorous and iron. The fresh early summer growth of these can be fermented in the same way as for nettle tea and used to make a nutritious liquid plant feed.

Finally, for those lucky enough to live within easy distance of the coast and near a beach with permission to forage, there’s seaweed, that plant-like group of organisms whose beneficial effect on soil and plant health is legendary. From boosting germination rates, root development, leaf growth and flower production to helping plants to fight off disease, this miracle worker is one of the organic gardener’s best friends. Just as for nettles, comfrey and field horsetail, it can be made into a liquid foliar feed, whether in combination with any or some of the above plants or on its own. It can also be used as a mulch, or to line the bottom of a planting hole or trench, or as a compost heap activator to speed up the process of natural decay.

For those of us who live inland, the next best thing is a good quality manufactured liquid seaweed feed. My favourite is the Irish-made Health-Sea Liquid Seaweed, a concentrated extract made from seaweed (Ascophyllum nodosum) sustainably hand harvested off the Irish Atlantic coast (fruithillfarm.com). At this time of year I give it as a diluted foliar feed every 10-14 days to all my young seedlings and transplants, and I swear I can almost hear them sigh with happiness ...

Q&A

Q: A lot of the soil immediately around our house is sticky, yellow-brown and very difficult to dig or to weed. I’d love to create some flower beds but it seems almost impossible. Is there any solution? – FJ, Wicklow

A: This sounds to me like a classic case of builders stripping the top soil off the site during the building process and then not properly replacing it, something that’s unfortunately still common. Your sticky, yellow-brown soil is in fact what’s known as subsoil, the infertile layer beneath topsoil. Unlike topsoil which is dark-brown, friable and full of organic matter, subsoil is lacking in organic matter, and is often stony, sticky and compacted.

As you’ve discovered, it’s difficult to garden on it. To improve it, you’ll need to use a garden fork to dig out any large stones or buried builders debris buried and then start adding plenty of well-rotted organic matter to any planting holes as well as a mulch in early spring and in autumn. This could be well-rotted farmyard manure, home-made garden compost or a commercially produced mulch (see enrich.ie; geeup.ie; and quickcrop.ie for bags of Envirogrind), or a mixture. It’s going to be a gradual process but you will slowly but surely see results over time as your soil becomes more fertile and easier to dig, and its structure improves.

You could also consider importing some good quality topsoil into the site. But bear in mind that this ideally needs to be spread to a minimum depth of 10cm for a lawn area and twice that for flower and vegetable beds. This is going to be difficult to do in the areas immediately around your house where the finished ground levels have been carefully designed to accommodate its damp-proof course as well as drains. But some well-designed raised beds retained with timber could be part of the solution.

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This Week:

Any remaining half-hardy vegetables and bedding plants need to be planted as soon as possible into their final positions in the garden or allotment if they’re to establish good root systems. If you’re moving them outdoors, make sure to harden them off first by gradually accustoming them to the cooler, windier, more variable growing conditions.

To revive young transplants and bedding plants before planting and help them establish quickly, nip out any dead or damaged flowers and leaves and then bottom soak their root-balls in a diluted solution of liquid seaweed feed. A scattering of slow release pelleted organic fertiliser gently forked into the planting hole will also help.