By Daíthi Turner

Why do we need fertilisers? If we look around, weeds and grasses seem to do well, often in places that look pretty inhospitable to plants. The truth is that soil fertilisation is at play constantly. Under the surface, the bugs, earthworms and bacteria churn, mix and enrich the soil quietly and out of sight. 

On the surface, there is the ongoing addition of food and nutrients through decaying vegetation and falling leaves, eventually being used by this thriving subterranean community. 

The most crucial factor is the demands we the gardeners place on the soil. If we are gardening for aesthetics, we desire the most vibrant displays of leaf and flower we can get. This places demands on the resources of the soil, and even more so if we are maintaining a kitchen garden. All that goodness on our table also has to be drawn from the earth. 

Nature Versus Nurture

One distinction I like to make that helps us understand the process is the difference between feeding the soil and feeding plants. I think the latter is the best way to proceed. 

Feeding the soil is a long-term fix and improves all aspects of the earth, including the life of the bugs maintaining the ground’s health. Sometimes a more immediate feeding is required, with some chemical additions showing almost instant results. 

On a related point, I was asked recently what the difference is between manures and fertilisers. Although there is a huge overlap in the definition of these terms, broadly speaking, manures are organic material such as compost, leaf mould, animal dung, and ‘green manures’. Fertilisers are usually more concentrated inorganic feeds like lime, ammonia and potash. 

Different plants require different nutrients, so the exact ‘diet’ for your soil is dependent on so many factors. There are books and commercially available kits to determine the precise make-up of your soil, allowing you to choose the exact requirements for the plants you wish to grow. But here, I will speak broadly about why to feed the plants and soil. 

Going Organic

I like to use primarily organic feeds if I can. You might not be lucky enough to have a friendly farmer who is only too delighted to offload a trailer of animal manure onto your driveway. I suppose he could dump it near the veg patch, but then I wouldn’t get to enjoy my children’s horror as they have to help me move it! 

There are other organic feeds for the soil we can use. Kitchen compost is an excellent supplement for soils and can be made in relatively small areas. Coffee grinds, organic paper, and vegetable peels are packed full of goodness that both plants and soils love. Those of us near the coast can salvage washed-up seaweed to add directly to our crops or compost heaps. Compost benefits from a good variety of organic matter. 

If you know anybody with chickens, the droppings are a precious source of nutrients but beware, they can increase the soil’s acidity, which some plants dislike. (Soil pH is a whole other discussion!). 

Giving Soil Comfort with Comfrey

Comfrey is a cornerstone of organic feeds for my garden. It is an excellent source of potassium. It grows wild and abundantly in these parts, but I have a few plants dotted around my garden for convenience. It has dense, lush foliage, and the pink flowers are highly rated by the resident honeybees, bumblebees, and hawk moths.  

Comfrey has been described to be a miner. It sends deep roots to extract nutrients from a depth most plants won’t reach. The leaves can be buried and will decompose, releasing the soil food. I’ve seen people line their trenches with comfrey leaves before they plant seed potatoes. I prefer to make comfrey ‘tea’. It’s a simple process. 

  1. Before the plant flowers, cut the leaves down and place them in a container with a lid. 
  2. Cover the leaves with water and put the lid on for about 4 weeks. The liquid left will be pungent and black. 
  3. Drain off the liquid and store it for use.  

You can make a more concentrated version that needs to be diluted, but your beans and tomatoes will love any comfrey tea! 

Many of us don’t have access or the need for a compost heap or a section of our garden devoted to soil maintenance. Still, I do think this broader discussion gives an essential context to the plant feeds we keep in the house for our indoor plants. Our potted plants are far removed from their natural state, so we must replace, as best we can, anything they need to thrive. When they flourish, they are a great addition to our living spaces!