The Benefits of Liquid Fertiliser

We’re at the point in spring where some plants can start to flag. You’ll notice it most in the vegie patch, where things planted back in late winter will have put on a big spurt of growth, but are now starting to look a bit tired as temperatures warm and winds increase. To revive sagging fortunes in the vegie patch and beyond, it can be a great idea to splash around a watering can or two of liquid fertiliser.

Gardeners seem to forget that plants take up nutrients in liquid form. In other words, when you apply a solid fertiliser such as pelletised chook manure, nutrients don’t get absorbed through plant roots until the pellets start to dissolve in the presence of moisture. By contrast, liquid fertilisers provide a quick response. The nutrients are taken up almost immediately through a plant’s foliage and root system. This enables the savvy gardener to correct any deficiencies relatively quickly, in addition to providing a rapid boost to plant growth.

To give you an example of this fast-acting process, I used liquid fertiliser extensively during last summer’s wet weather. Heavy rainfall leaches nutrients from the soil, and as a consequence, some plants may show obvious signs of being “hungry”. Citrus trees, being gross feeders, were particularly vulnerable to nutrient deficiencies last summer, so once the soil had dried out a bit, I applied a solid fertiliser around the root zone of my trees to provide a slow release of nutrients. But that’s not all. I did so in tandem with fortnightly applications of liquid fertiliser. Until the solid fertiliser started to break down, the liquid fertiliser provided a rapid boost. The result was that the plants remained green and healthy all summer long.

Two other situations where liquid fertilisers really come into their own is with container plants, and leafy green vegetables. Plants such as lettuce, rocket, bok choy, and silverbeet will produce lots of tender leaves in response to regular applications of liquid feed, while container plants benefit greatly from monthly doses of liquid fertiliser as a supplement to slow release products. Indoor plants in particular are prime candidates for regular liquid feeding during the warmer months of the year.

At this point, some of you might be wondering what I even mean by the term “liquid fertiliser”. So let’s define it. A liquid fertiliser is any liquid containing nutrients essential for healthy plant growth, including nitrogen, phosphorous and potassium. Liquid fertilisers shouldn’t be confused with liquid plant tonics. These products are often based on seaweed extract, and generally contain trace elements and other helpful micro-nutrients, but very little nitrogen. Rather than promote foliage growth, tonics enhance soil life, encourage healthy root formation and provide other benefits such as making plants more resistant to frost and drought.

Liquid fertilisers, on the other hand, come in a wide array of different configurations based on the ingredients used in their manufacture. The most basic are very low-tech and can be entirely home made. Human urine (don’t cringe) has been used as a fertiliser for thousands of years, and there’s still merit in having the gentlemen of the house say good night to the lemon tree. At home you can also make liquid fertiliser from the worm juice that accumulates in the lower chamber of your worm farm, or from comfrey or soft weed leaves steeped in a bucket of water for couple of weeks.

Some organic gardeners make a compost tea by placing about one litre of compost in a shadecloth “teabag”, putting the bag in a 10 litre bucket, and letting the liquid brew for a week before use. With any of the above fertilisers it’s important to dilute to about one part concentrate to 10 parts water.

When it comes to commercial products, nurseries and hardware stores carry dozens of different liquid fertiliser brands. Being an organic gardener I choose products that are made from previously living ingredients, rather than synthetic chemicals. My favourite liquid fertilisers are based on fish emulsion, and in my view the best of the lot is Charlie Carp. I generally avoid endorsing a product specifically, and never accept payment or kickbacks for such recommendations, but I love the fact that Charlie Carp takes a problem – feral fish infesting our waterways – and turns it into a fertiliser for plants. Brilliant. There are lots of others available as well, but it would pay to look for those that are Certified Organic.

The only other caveats I have with liquid fertilisers is to always dilute them according manufacturer directions, to avoid burning sensitive plant roots, and to not ignore the long term process of building healthy, fertile soil via the continual addition of decomposed organic matter. Liquid fertiliser can be helpful, but soil building is still the main game.

First published in the Toowoomba Chronicle 22nd October 2011. Photo by Justin Russell, orange blossom.

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Tagged as: Organics, Spring