Feeding plants from the top down

Every gardener who has tended a patch can relate to the old adage that ‘no one soil is the same as another’. This diversity is evident even within the confines of our trial and production gardens here at Diggers, where we see soil type, soil structure, organic content, pH and even nutrient availability not only differing across the site, but even between two adjacent beds.

Across the various beds that make up our trial and production site, we have observed very different plant responses to soil-applied fertilisers, and in some cases, no plant response whatsoever. Often the addition of soil-applied fertiliser or amendments directly to the plant root zone, especially in alkaline soils, can bind up many of those elements, making them unavailable for plants. Furthermore, the tendency of gardeners to overapply fertiliser because of the initial limited plant response can create further imbalances and lead to nutrient deficiencies.

So how can we counter this issue of our plants not responding to soil-applied fertiliser? Whilst there is no ‘one size fits all’ solution, the use of foliar-applied amendments is a very effective method of ensuring that high percentages of the applied nutrient is made readily available to the plant. ‘Foliar feeding’ or foliar applications are liquid fertilisers delivered directly to the leaves, stems and bark of the plant. The leaf surfaces of plants are very efficient at delivering nutrients directly into their internal circulatory system, and we have observed initial responses in crops in as little as a few hours, with significant responses experienced over three to five days. The bonus for gardeners is that most of these broad spectrum, liquid fertiliser amendments can easily be made at home from materials with little to no cost.

Fermented plant amendments

Many organic gardeners will be familiar with comfrey tea but is there any real validation to the idea that certain plants fermented in water are super-fertilisers? Well yes, and no. In fact, all plants accumulate elements from the soil and transport them to the surface, with these elements then being stored in the tissue of the plant itself. This is also true of weeds – after all, weeds are just plants growing in the wrong place. Certain plant species also have an ability to accumulate and concentrate specific elements from the subsoil. By chopping and placing the plant material in a large bin, filling it with clean water and leaving it sit covered for six months, we are extracting these stored elements into a liquid that we can dilute and spray as a foliar application. We’ve had very positive results by fermenting comfrey, lamb’s quarter and chickweed, with the latter being high in phosphorus (P), iron (Fe) and manganese (Mn). We use these as a standalone amendment or we blend them with purchased organic liquid fertilisers.

Vinegar extractions

In some cases we need to apply specific minerals as either a prevention for certain diseases (e.g. blossom end rot in tomatoes) or to drive a certain stage of growth in the plant. One amendment that is easy to make is a calcium extraction. We are fortunate to be located near the coast, which means we have access to plenty of restaurants with an excess of shucked oyster shells, an otherwise wasted byproduct. You can also use eggshells or, for a higher phosphorus content, cow bones.

At scale, we use 10kg of cleaned and dried oyster shells with 20 litres of organic apple cider vinegar, but for the home gardeners, this could be done using a small 500ml jar at the same ratio. Cleaning the shells or bones and drying them in the oven will give you the best results when you combine the vinegar and the shells. The acid in the vinegar reacts with the calcium carbonate in the shells, extracting a water-soluble calcium, which can be left in a dark location indefinitely. We mix 30ml into 15 litres of water, usually applying early morning to the crops, and in combination with our other amendments, resulting in strong root and vegetative growth that is sustained throughout the reproductive stage of the plants’ development. We observe stronger, thicker stems that are resistant to snapping or breaking, particularly in our legume and tomato crops. Twenty litres will last us just over a year.

We are currently experimenting with several ferments and extracts. We use weeds that are part of our seasonal profile (dandelions, orchard grass and lamb’s quarters), as we know they are great accumulators and are readily available on-site, as well as fish waste from our local seafood supplier. Most of these will be prepared now, ready for foliar applications during the coming spring.

Written by Jason Buchanan, Diggers trials and production.