Winds from Africa, Part Three

by Jonathan Hull

The first two essays (Winds from AfricaPart One and Part Two) in this series explored the role of dust in nature from the biosphere to the microscopic world of plant leaves.  We now turn to the garden.  What are some practical applications of these discoveries?

Foliar sprays have been one application discussed throughout this series.  I’ve used them for years, but this past season was the first I’ve done so consistently.  The results I observed in the garden, in combination with deeper research into the topic, have convinced me to expand foliar spray use. 

Figure 1

[Photo: Author’s Kitchen Garden]

These sprays have numerous formulations tailored for specific purposes.  Some you can make with what is readily available, while others require the purchase of specialized materials.  In researching this topic, I realized describing these formulations in detail would require a small book.  In this essay, I will offer a few guidelines for general use, and later a peek into the most exciting aspect –  targeted foliar applications.

I prefer making things myself because it is often the ecologically responsible option.  There are numerous DIY foliar sprays one can make, and later I will detail one of these.  However, until I’ve mastered the ability to consistently make and use my own formulations, I’ve decided to not let the perfect stand in the way of the good.

For general use, I opted for a solution easily purchased from a garden center.  This is liquid fish hydrolysate mixed with seaweed concentrate.  (Note that fish hydrolysate is different than fish emulsion.)   The hydrolysate/seaweed spray provides plants with a broad spectrum of nutrients, but above all, phosphorus.    Why is phosphorus so important? Phosphorus is nothing less than the currency of life! Every movement of every living being from plants to humans requires the expression of phosphorus.

Several brands include appropriate doses of phosphorus and other nutrients, but the one I used was Neptune’s Harvest.   I followed instructions on the label, and began by diluting the concentrate with water.  For reasons we will consider later, dawn is the best time to apply – dusk is second best.  For a simple schedule,  I adopted a weekly routine of spraying every plant in the garden, especially during spring, early growth, flowering and fruiting.                

A sprayer is the main tool you will need–one that  mists, not the flat spray jet some sprayers employ.  Solo brand sprayers ( have worked well for me.  I have a small half-gallon version I use for seedlings and other small jobs.  I have another three-gallon sprayer I lug around the garden, but this year I will be looking into a more ergonomic backpack sprayer. In any case, you will want a spray that mists up as well as down since you will want to coat the entire surface of the leaves, especially the underside.  Many plants have the majority of their stomata on the underside of the leaf.

This is a bare bones general use application that is sure to give you good results.  For more applications, the best guide I have found on the subject is the chapter “Foliar Nutrition” in Jerry Brunetti’s book The Farm as Ecosystem.

Putting Foliar Sprays into Context

The most exciting aspect of foliar applications is not their content,  but their context.

Figure 2

[Photo: Author’s beneficial insect garden]

When I set out to write on this topic, my intention was to describe foliar applications analytically…take the subject completely apart in order to show how it works.  Obviously, I decided to do otherwise.  One reason, as I’ve mentioned, is that it is a big subject with a lot of complicated details.  But more than this, my decision to take a different approach was to push myself to try a different way.

I’ve inherited a cultural tendency to view the world exclusively from a linear analytic perspective.  I like tools and I like to study different techniques.  This perspective is a great way to gain knowledge, but it is often a terrible framework from which to act.  I can trace most of my mistakes and inefficiencies back to the fact that I had acted with a tool in mind instead of the context of its use.    

Nature is rarely linear and its systems are complex, dynamic and adaptive.  One of the many reasons I garden is to explore, enact and embody a holistic perspective.  For similar reasons I’ve approached this series as an experiment in how to describe a technique holistically.

If we view the garden holistically as a complex adaptive system, what role can foliar sprays play?

Foliar applications find their most effective use if we understand that plants are the structural expression of the relationship between countless processes.  If we are to engage responsibly in these natural processes then we must have some familiarity with them.  Yet it is impossible to understand such a complex world directly.  What is to be done? 

We can represent the relationship between garden processes in a kind of shorthand – patterns.  Patterns work much the same way as metaphor.  The pattern I’ve used in this series is the relationship between the elemental processes of nature: sun, wind, water earth and the role of life knitting it all together.  The vitality of any one plant could be understood as a particular expression of this pattern. 

A plant in our garden is embedded in this pattern of elemental processes as it extends through the biosphere and deep into its history; but also in a different, yet similar, expression of this pattern in the microscopic realm on the plant’s leaf.

The fractals of nature
The fractals of nature

[Photo: Plant leaf showing fractal self-similarity.  From:]

The journey we took in Parts One and Two went through these different scales to show that patterns are fractal.  Fractals are shapes that show self-similarity when you view them at different scales.  One branch of a river has a similar shape as the whole river.    This perspective allows the pattern at one scale to inform our investigation of another. 

Here is just one example of how a pattern, in all its metaphoric power, came together in my garden.

My garden, Africa, and the Amazon

I had just finished spraying the plants in our garden.  The sun was beginning to rise and its light was playing off the water droplets that were clinging to the plants.  The birds were in full morning chorus.  I was feeling the quiet, anticipative energy that comes at dawn. 

The solution I sprayed was one that I picked up from a school of fertility management called Korean Natural Farming.  It is a phosphorus solution made from animal bones.  Here is how I made it.

Some time ago I started saving leftover bones from chicken and beef that we get from a local farmer.  When I had enough of them, I cleaned the bones by boiling them in water.  (As a bonus I got soup broth).  I then let the bones dry, then charred them in a small stove of my own making, one that is usually used to make charcoal for biochar.   I then soaked the bones for three weeks in apple cider vinegar to dissolve them into a solution.  I diluted this solution further until it had a pH of 5.5, the same pH as  plant sap.  I then put this diluted solution into a garden sprayer that dispenses a fine mist and covered the entire surface of all the leaves in the garden.

Figure 4

[Photos: Author’s biochar stove (above)

Bone char before acid soak (below)]

Figure 5

If you recall from the first essay in this series, the fertility of the Amazon rainforest depends in part on the phosphorus contained in dust that originates in the Sahara.  A significant portion of this phosphorus is from the bones of ancient fish.  When it  travels across the ocean, this phosphorus is transformed by an acidic weathering process that occurs in the upper atmosphere.  As described in part two, when this dust settles on a leaf it starts a process by which a solution is spread over the leaf.  This triggers the opening of stomata whereby the phosphorus moves into the interior of the leaf where it can be used in the plant’s metabolism.

This entire array: ancient phosphorus weathered from soil, complexed by ancient fish, eroded into dust particles by desert winds, acidified in the atmosphere, put into solution on plant leaves – was the expression of the same pattern that I had just used in the garden!

It dawned on me that the solution I was spraying, and the processes by which it was made, was unintentionally mimicking a natural process of global nutrient cycling. 

Both begin with animal bones, which contains a special form of  phosphorus.  Since the phosphorus  was structured by one set of living processes it is easily used by others.  Charring bones weakens their crystalline structure, making the bones easier to dissolve—thus  mimicking the decomposition of bones by desert sand.  Soaking the charred bones in vinegar mimics the process of acid leaching as it occurs in the atmosphere.  By spraying the solution into a fine mist you mimic the way in which African dust settles on Amazonian leaves.


The timing of the application was also orchestrated to harmonize with the pattern of natural forces  occurring at the microscopic scale.  The best time of day to spray is in the predawn hour.  Why might this be?  Our discussion in Part Two gives us some clues.

Figure 6

[Photo: Sunlight in morning dew.  From:]

Plant leaves utilize a self-regulating system, the opening and closing of the stomata, to balance the need to breathe with the loss of water.  Higher temperatures cause more water to evaporate, so that above 85 degrees a plants will close all of its stomata.  By contrast, cool early mornings allow stomata to open their widest and breathe their fullest. (It has even been suggested that the specific frequency of morning bird song encourages the opening of plant stomata!)

Of equal importance to the foliar sprayer, predawn is also when humidity and dew are most concentrated, thus providing a ready-made liquid avenue into the leaves for your phosphorus solution..

I also time phosphorous application to the developmental stage of the plants.  Phosphorus is in highest demand when plants are in early stages of growth.  A lack of critical nutrients early on can dramatically reduce later growth.  The so-called epigenetic system of a plant senses the lack of nutrients and curtails the plant’s developmental path.  Perhaps the system designates a smaller frame of growth or limits how much fruit the plant will set.  The plant may still benefit from supplemental phosphorus later in life, but in a certain sense the die will have been cast.  In my experience, a small targeted application of phosphorus early in the year dramatically tips the balance of later growth.

Foliar spraying tips the balance of underground growth, as well. In this case, it is the growth of plants’ natural allies in the soil, the mycorrhizal fungi. These fungi, using powerful enzymes, break down the inorganic compounds where recalcitrant phosphorus typically resides and make it available to the plant. In return, plants feed the fungi energy in the  forms of various plant metabolites they produce by photosynthesis.      

Figure 7[Photo: Mycorrhizal fungal threads attached to plant roots.  From:]

It’s a virtuous cycle.  The more energy a plant can capture from the sun and bind to phosphorus the more it can feed the fungi, which in turn scavenge more phosphorus from the soil to transmit to the plant.  But the cycle can also reverse.  If the plant lacks sufficient phosphorus by which it transfers metabolites, it can’t feed the fungi, which then can’t access soil phosphorus. The whole web suffers.

Conventional soil agronomy “fixes” this problem by applying preprocessed, soluble phosphorus.  Many plants then grab the freely available phosphorus and yield to the temptation to abandon their mycorrhizal partners.   In so doing, plants inadvertently abandon other fungal benefits, including disease resistance.   They also make themselves dependent on  still more preprocessed inputs.                     

Here is the context for the incredible potential of foliar applications. 

The phosphorus solution I sprayed, much like what is found in the dust from the Sahara, was in a highly bioavailable form.  Unlike phosphorus in the soil, the plant did not need to expend energy to get it.   By spraying it on the leaf, we bypass the potentially sluggish channel that moves from the soil, to fungi and then to the plant.    Unlike conventional applications of phosphorus to the soil, foliar spray does not short circuit the natural plant/fungal symbiosis.  In fact, spraying small amounts of foliar applied nutrients can actually jump-start interactions in the soil food web!  The plant will use its free gift of energy to give its allies in the soil a leg up.  The virtuous cycle is reinforced.      

Imagine foliar sprays as the equivalent of acupressure in body work:  small, targeted acts that have whole body effects.  Plant health is largely determined by interactions in the soil, but foliar nutrition can be the tipping element that drives the whole system into new states of health.  We’ve seen something similar in the first essay.  The changing orientation of the earth with the sun was thought to be the main driver of climate change in the Sahara.  But it was also determined that atmospheric dust was a “tipping element” that shifted the climate back and forth between different states.

Understood in this way, foliar application can be the tipping element in the creation of healthy soil itself!  Plants are known to channel anywhere from 50-80% of the energy they obtain from photosynthesis into the soil.  They do this to support a diverse suite of microbes (both fungi and bacteria) that facilitate plant nutrition and health.  The healthier the plant, the more energy it can channel into the soil, the more microbes, the healthier the plant: another positive feedback loop.  This represents an incredible input of energy into soil that can affect its physical, chemical and biologic characteristics.  Foliar sprays that precisely target plant nutrient deficiencies can tip the balance of plant health and let the plant drive its own soil rehabilitation!


IV. Integrated Gardening Techniques Produce A Vibrant Food Web

This bring us to an important point.  Foliar applications are no silver bullet!  It is most effective when use in conjunction with other techniques that build healthy soils.  

The most successful of the soil building techniques I’ve employed to this end are the following: water harvesting earthworks, deep mulching, cover cropping, composting with specific microbial communities, soil mineralization, subsoil de-compaction, no-till methods – to name a few.  Foliar spraying is one of the newest techniques I have integrated into my practice. 

figure 8 

[Photo: Author’s “Storage Garden” with water harvest earthwork (aka swale) at lower right]

For instance, I keep one garden bed a year growing a cover crop through the whole year.   I spray this cover crop throughout the year, both with a broad spectrum foliar spray, but also with ones containing minerals found to be deficient in soil tests.  Vegetative growth can be quite phenomenal.  But more importantly, the soil condition after this cycle is equally incredible.  I’ve applied compost to the garden for years and I’ve never seen the dark “crumbly” tilth that I’ve encountered by incorporating foliar sprays..

I’ve got a long way to go, but I’ve already witnessed remarkable  improvements in my garden.  Insect damage has shrunk dramatically. We used to dust our beans with Rotenone because the beetles would reduce the leaves to skeletons.  The same with our cabbages and the damage done by caterpillars.  By no means have these creatures disappeared from the garden, but they do so little damage now that we only occasionally pick them off our plants.  The organic pesticides we’ve used in the past are now sitting unused on the shelf.    

Species diversity in the garden has burgeoned.   I use foliar sprays not just on our vegetables but also in those parts of the garden I reserve for plants that attract beneficial insects.  Now instead of Japanese beetles and cabbage moths, our garden is overrun with their predators: assassin bugs and parasitoid wasps.  More beneficial insects are attracted to the plants because the nutrient quality of the flower nectar and pollen has increased.

Figure 9  

figure 10

[Photo:  Beneficial insects in author’s garden. Above and below  Assassin Bug and Syrphid Fly 

Yields have also gone up.  One of our most successful plantings was butternut squash in a 30 inch raised bed 30 feet long.  From this area we harvested over 175 pounds of squash – easily doubling, if not tripling,  yields.

Nutritional quality of our vegetables, herbs and medicinals has also increased. Brix levels (the standard nutritional measurement) has increased, as well as taste.  It feels great to eat this food.

figure 11

[Photo: Partial harvest from Author’s “Storage Garden”

V. Connecting With The Earth

“The ultimate goal of farming is not the growing of crops, but the cultivation and perfection of human beings.” Masanobu Fukuoka, in One Straw Revolution.

Maintaining a diverse, productive garden can be a complex and demanding task.  It is easy to adopt a head down posture while in the garden, a kind of habit that relates to it only through a veil of tasks to be completed.  Circumstances prevailed in piercing this veil.

A spark of inspiration sent me on this journey.  A meditative moment in the garden revealed a pattern connecting an astonishing relationship: between dust storms in Africa, the fertility of the Amazon rainforest and my use of foliar sprays in the garden. 

Foliar spraying was a garden chore transformed into work done in harmony with the elemental forces nature; an interplay between the sun and earth, water and air, plant and soil.

I felt the deep metaphoric power of the process I helped initiate.  Using fire to transform bones into life-giving dust, working with the rhythm of the sun to use water in the air to channel these nutrients through leaf stomata to living communities unseen in the soil.   As I moved across this landscape from the biosphere, to the garden and down to the microscopic; I found myself in this pattern – playing a tiny part in life’s work of knitting it all together.  It was a brief moment of connection – of being deeply aware of being alive.  This, I thought, is why I garden.