Food Forests and Natural Pest Control – Observations

Hearing Geoff Lawton speak about the effectiveness of natural pest control in food forests during my PDC studies is what originally prompted me to design and build a backyard food forest garden. Nature taking care of pests in the garden? It sounded too good to believe, and coming from a science background, I just had to test the concept out. After all, any good science can be replicated!

Four years later, after working out how to scale down a food forest into an urban backyard, and going through the designing, building, documenting and weighing of all produce, I inadvertently had created Melbourne’s first demonstration urban food forest and a proof of concept experiment that had more far-reaching outcomes than I first envisaged. Hundreds of people visit the garden each year to see it first hand and learn how it all works. Even our local government has taken a liking to the concept of permaculture and I’m often hired by them to present on the topics of permaculture and sustainable gardening to an equally interested general public. I put it down to a good teacher!

The garden productivity has been fantastic, and has been increasing steadily from year to year, but what has been even more impressive is how the garden I first designed has become a living ecosystem that has taken on a life of its own. Geoff warned us that would happen! With passing time, the system has increased in stability and resilience and the pests have clearly reduced. I would like to share some observations in this article which clearly demonstrate the proof of concept of natural pest control in food forests.

 As a long time organic gardener I relied on organic pest control measures — horticultural soap, neem oil, organic white oil, and, as the last resort, natural pyrethrum. All pretty mild really, but it takes time, money, effort and energy to use these pest control measures. When I first built my food forest garden, pests came, as you would expect. Having planted all the requisite companion plants which repel pests and attract beneficial predator insects, I had to exercise extreme restraint, to let the companion plants grow, and allow the beneficial insects time to establish themselves. It’s just through sheer lack of patience that many  people don’t succeed with natural pest control measures.

While it was excruciating to watch the pests pick off a plant here or there, the forest style planting pattern minimised losses by nature of the design. If the pests found a lettuce plant which somehow succumbed to attack, they would have to work real hard to find the next one, which wasn’t predictably planted right beside the other one as in most gardens, but instead in some other random part of the garden.

After six months, the food forest came to life, and the natural pest controls kicked in by themselves. Soon the whole garden was swarming with ladybirds, predatory wasps, hoverflies, praying mantises, lacewings and all manner of beneficial insects. The pests started disappearing. Plenty of perennial plants ensured that there was a permanent home for the beneficial insects to overwinter in, and an abundance of the right kind of flowers ensured that the good bugs had an alternative food source to keep them alive after they ate all the bad bugs.

The result: all pests were eliminated except for snails and cherry slugs. Not a bad start. You might be wondering how I know it was the design of the garden that brought the pest problem under control. The answer is simple — proper experimental design! With formal training in science, I know that every good experiment requires a control — a separate test where the thing under investigation is not treated, and does not receive the thing being tested. So, how do you not apply the benefits of nature to a garden? Simple, set up an artificial one, and there’s nothing more artificial than a hydroponic system, or even better, two hydroponic systems at different distances from the main organic garden to also determine if beneficial insects will travel some distance.

The Experimental Control

The experimental control system is no token system, it’s actually quite a large (and expensive) hydroponic ‘Autopot’ system.

Pictured below is the hydroponic setup near the garden. It’s on the left with the three green tanks in the middle of it. You can see how close it is to the main garden — a mere 1.5m (5 feet) away. It’s currently growing rock melon, watermelon. three varieties of tomato, snake beans and basil. It extends around the corner where there are more hydroponic pots growing butternut pumpkin, capsicum, and the herbs soapwort and ashwagandha (Indian ginseng).

A closer look at some of the hydroponic tomatoes:


This part of the system is comprised of twelve 10” pots, which use either perlite, scoria or clay balls as the growing medium. The medium only anchors the roots, and wicks the water-nutrient mix upward to the plant roots as a bottom watering or sub-irrigation system. This system uses a wet/dry cycle ‘Autopot’ valve which fills the trays with water, allows them to dry out for a while, then refills them when the plants need the water. It’s a passive, gravity fed system — no power required.

It all faces the midday sun (north in the southern hemisphere). Just like the main garden, it receives a fair bit of morning and midday sun, and some afternoon sun. It has an unlimited supply of water/nutrient fed through three 35 litre nutrient tanks (which I have to refill before they run dry!). The nutrient is a two part mineral salt fertilizer mix, which provides the usual N-P-K and a host of trace elements. Note, there is no soil or organic potting medium in this system.

The second part of the system consists of two 10” pots and four much larger 12” posts. The same range of growing media is used here. This system is about 6m (20 feet) from the main garden. The wall is over 4m (13 feet) high and is covered with a 4” (10cm) wire mesh grid supported 15cm (6”) away from the brick wall behind it. It’s growing deciduous climbers, three grape vines, and lots of climbing beans which shade part of the house’s west wall from the hot afternoon sun in summer. There’s also a dragonfruit (a climbing fruiting cactus) in there, and some oca (NZ yams) and the herb brahmi, just for the heck of it! It’s fed by one 220 litre (44 gallon) recycled plastic drum nutrient tank.

As you can see, it’s close to my blue rainwater storage tanks, so I can easily fill it with rainwater. It uses the same nutrients and growing media as the rest of the system. As is evident from the picture, there is abundant growth, the climbing beans routinely reach a height of over 3m (10 feet) and the grapevines have reached the house eaves and are hanging back down, they are well over 5m (15 feet) long.

In case you’re wondering, no, this is not an advertisement for hydroponics. I’m just explaining how a high end hydroponic system is set up for a controlled experiment alongside an organic garden, a food forest. The point is to show that the hydroponic system is not at any disadvantage, as it has the same amount of light as the organic garden, and way more water and nutrients!

The system this is being compared to, my food forest garden, is described at length in my article Lessons from an Urban Back Yard Food Forest Experiment, so for the sake of brevity I won’t repeat it here.

The Observations

Working with both the food forest system and the hydroponic system has been quite a learning experience.

There’s nothing quite like learning something from first hand experience — it really consolidates your knowledge in quite a major way. The hydroponic system, being so unlike a living ecosystem, has really reinforced some ecological and horticultural concepts for me.

All machines do fail, especially if you don’t keep an eye on them. The hydroponic system furthest from the garden was bursting at the seams with climbing beans two years ago when the unimaginable happened, the watering valve somehow got stuck on a very hot day (a very rare occurrence, roots crept into the watering valve and jammed it), resulting in a wall of wilted beans. We’re told when plants wilt badly this results in damage to the plant. I thought if I restore the water supply they’d soon come good, and as expected, they did.

Within a few days, the climbing beans got attacked by spider mites — tiny red mites which suck the sap out of the leaves. They look like tiny red dots on the underside of the leaves and when you rub your finger over them it leaves red steaks on your finger. With severe infestations they make a fine silk web, hence the ‘spider’ part of their name. They hate dampness and are particularly fond of dry conditions, so I often sprayed water, and I think I used horticultural soap on them, which just suffocates them. Within a few weeks, the beans were fine again, and then the water valve got stuck a second time! Soon, the mites were back, and then they knocked the vigour right out of the climbing beans, and the yields were very low. There were about twenty or more plants growing.

This was clear confirmation that pests don’t attack plants to spite us! They also don’t attack healthy plants (most of the time!) Plants have evolved their own defence mechanisms against pests and diseases over eons, and when plants are growing in the right place, with the right amount of light, water and nutrients, they grow strong and healthy.

When the conditions aren’t right, plants gets weakened, and then become vulnerable to pests and diseases, just like a person with a weakened immune system. It is clear that the two drastic water shortages weakened the hydroponic beans enough that the mites moved in to finish them off, as an instrument of natural selection. That’s what pests do, eliminate weak plants!

One lesson to take home here is that if your plants are being attacked by pests or diseases, rather than seeing it as an act of war and responding accordingly like most farmers and conventional gardeners do, and engaging in wholesale chemical warfare, we should instead ask ourselves why is this happening?

  • Is the plant in the wrong position in the garden?
  • Are any any nearby plants either bad companions, over-competitive  or allelopathic?
  • Is there too much or not enough light?
  • Is the soil too wet or too dry and does it drain or retain moisture enough?
  • Is the plant even suited to this climate?
  • Is it a strong and pest/disease resistant plant variety?

Trying to prop up a plant artificially where conditions are detrimental to it is ultimately a futile exercise, and it just unnecessarily prolongs the agony, and wastes lots of resources unnecessarily. If you recreate the conditions to which a plant is suited, it will thrive with minimal assistance.

Back to the main topic, food forests! Here in Melbourne, Australia, our climate is erratic at the best of times. Our weather is commonly described as having ”four seasons in a day”. To make matters worse, in the last three years, the weather has gone completely haywire. No one in Melbourne doubts climate change, that’s for sure! Our temperate climate has seen episodes of hot, wet tropical weather, extreme rains, sudden extremes of  heat and more recently periods of extreme dryness and cold autumn weather in summer.

This climatic change is making a real mess of the seasonal cycles and we’ve seen pest populations emerge at odd times of year. During our December/January/February summer period we’ve seen an explosion of whitefly. Melbourne has been hit by whitefly in plague proportions — everyone’s garden is filled with these tiny white miniature moths which erupt into the air in flocks like a small white dust cloud when disturbed. These pests are sap-suckers and seriously weaken plants, and since they have a very short breeding cycle, they multiply quickly, and are hard to control without very frequent spraying.

Like all gardens, they appeared in my garden in early summer too, and I trusted enough to not worry about them. Within around three weeks, they disappeared completely from the plants and trees in the food forest area. Then soon after that they also disappeared from the hydroponic setup nearest the garden. Into the third month of summer and everyone I speak to is still having problems with whitefly. I checked my hydroponic system furthest from the garden, and it too has a huge whitefly problem.

Here is the tell-tale damage of a bean leaf attacked by whitefly, from the hydroponic system growing furthest from the food forest.

Here is one of the grape vine leaves, the whitefly is visible on the leaf here.

Curious to see how the very same plants in the food forest were faring, I checked my climbing beans, and they were in perfect condition, untouched by pests. These beans are the same variety as the ones growing hydroponically — ‘Blue Lake’ climbing beans.


I also have a sultana grape growing in the food forest. Two of the four growing hydroponically were propagated from this one, so they are exact genetic clones. When I checked the grapevine, not a single pest could be found.

This sultana grapevine in the food forest extends over a bamboo arch I constructed, and runs alongside the house, right next to the closest hydroponic system. Incidentally, the tall grass in the background to the left is sugarcane, and there’s a pumpkin creeping out of the terraced garden bed on the right!

It is evident that the very same grapes and beans growing organically in the food forest are unaffected by pests while the ones growing in supposedly superior conditions hydroponically are being attacked furiously by pests.

The reasons? The food forest is pest free because it is a living ecosystem filled with life that maintains its own balance, whereas the hydroponic system is a sterile, lifeless growing system where the plants are left to fend for themselves. How do I know this? Observation. Bill Mollison stresses the importance of observation in permaculture, and for a good reason. You can learn a lot from Nature! As I sometimes just sit and watch the activity in the garden I notice insects moving to and fro, and I pay most attention to the beneficial predatory insects. There is a lot of beneficial insect life observable in the food forest, but I see the good bugs visiting to the hydroponic systems only occasionally.

The beneficial predatory insects are found most commonly in or around the perennial plants where they shelter, and especially around any plants that provide an alternative food source, like nectar. These beneficial predatory insects don’t have long mouthparts like the butterfly’s coiled proboscis, which it can extend deep into flowers. Ladybirds, hoverflies, etc. have short mouthparts, so they can only feed from shallow flowers, so I grow lots of these flowers. I’ve listed a few of them below, along with pictures of them from the garden:

1) The Umbelliferae family, which includes carrots, parsley, dill, cilantro, fennel, chervil parsnip, celery, and celeriac — named after their umbrella  shaped flowers, called umbels.

Ladybird on a carrot flower

A parsley flower, with the distinctive ‘umbel’ shape

2) The Compositae, or daisy family (also called the Asteracea, or aster family), so named because the centre is in fact a composite flower, consisting of a cluster of many little flowers called ‘florets’, with one set of petals around them all.

Feverfew, a medicinal herb, with the characteristic daisy flowers.

Yarrow, a medicinal herb which has carrot-like flowers and foliage,
is also a member of the Compositae family

Other plant families also have small flowers that can serve as a food source for beneficial insects:

Alyssum, an ornamental flower from Brassicaceae (mustard) family

The second key feature that makes a food forest pest resistant is a rich, healthy, undisturbed soil which is covered with lots of organic matter, which acts as a mulch and slowly breaks down, releasing nutrients into the soil. Remember, it’s all a no-dig system, just like a real forest! The decomposing organic matter hosts many tiny organisms, including beneficial mites, many of which are predatory and will eat pest mites and the eggs and young of many pest species. In a hydroponic system, which has an inert growing medium, the whole soil ecology is eliminated. The beneficial mites in the food forest’s rich, mulched, sheet composting system would be responsible for eliminating the whitefly. Firms which specialise in biological controls actually sell mites for controlling whitefly.

It follows that If you dig up your soil, have bare exposed soil, or use chemical fertilisers, they you destroy your soil ecology, so it becomes little better than the inert hydroponic growing medium. If you have pests, look at your soil!

Comparing the two hydroponic systems, I have been able to determine the approximate ranges that insects can traverse to get to pest infested plants. Firstly, with caterpillars, none ever appear in the food forest, and neither do they appear in the hydroponic system which is 1.5m away. I have watched the predatory wasps as they aggressively patrol, checking leaf after leaf, looking for caterpillars. They appear to rest at times near the water garden, possibly because of the cooler microclimate and water source, and they launch their patrols from there. They appear to fly all around the yard without any problems, but because the distant hydroponic system is situated down a long path between house and garage that is closed off at one end, they are less likely to venture there out of routine, so I rarely see them there. Caterpillars do appear on the grape vines of the distant hydroponic system and usually last for about two weeks before the wasps locate and eliminate them.

From my observations, smaller insects don’t range as far across areas where plants are absent to get to food sources, even if they can fly. Tiny hoverflies will actively patrol the food forest, and make occasional forays into the hydroponic system nearest the garden, but rarely ever venture into the hydroponic plants located 6m away, in a partly secluded area. I’ve made a similar observation for ladybirds. I have often heard that ladybirds are fond of laying their eggs on nettles. I routinely leave nettles to grow beside one of my citrus trees, and I find they are definitely teeming with ladybirds, year after year. The nettles also work as dynamic accumulators of minerals, which enrich the soil when they die down. They’re also edible and highly nutritious! Each element serves more than one purpose in a design — that’s what we look for in permaculture.

Nettles are a ladybird attractant plant and a
dynamic accumulator of certain minerals

Praying mantises are voracious pest predators, and even though they do fly, they seldom do so as they may get eaten by birds. They mainly walk slowly, leaning to and fro as they move, emulating a swaying leaf in the wind. They will avoid crossing open ground at all costs, but often venture through climbing plants quite happily, and I have found that extensive vertical gardening trellises adjoining the main garden create ‘highways’ for them to forage through searching for prey. Visitors brushing past my raspberry trellises as they walk past sometimes find a praying mantis has hitched a ride on their clothing!

I’ve also noticed that Nature can be quite ingenious, and just like in warfare, for every attack, there is a counterattack, and for every counterattack, there is a defence. One pest insect I have observed often is the harlequin bug, or shield bug, those strange black and bright orange coloured bugs that always appear to be mating! They are described as quite destructive, and no matter how much wildlife and beneficial insects you attract into the garden, nothing will eat a mature bug. Their bright colour is a warning to predators, and they’re called ‘stink bugs’ for a reason — they emit a pungent odour when squashed, injured, threatened or disturbed. I’ve found they have a preference for a particular plant, the herb Horehound. Despite their reputation as destructive sap suckers, they haven’t been able to damage this plant in any way. It appears to be what we call in companion planting a ‘sacrificial plant’ or ‘decoy plant’, a plant that can draw away pests from other plants, and yet is hardy enough to withstand the pest damage and still produce seed to reproduce. Furthermore, it’s drought tolerant, grows in poor soil and is an important  medicinal herb as well. Another plant that serves more than one purpose!

White Horehound or Common Horehound (Marrubium vulgare)

So far, it’s all been a fascinating experiment. There is still more work to do, more things to try — it’s one never-ending experiment and a great hands-on learning project. This hydroponic system easily converts into an aquaponic system, so that’s one for the future. I’m still working on more natural pest control measures too. To deal with the snails I’m in the process of setting up several lizard habitat areas, as I’ve seen skinks and geckos lurking around. If I give them a home, they will hopefully come and stay, and feast on the nasty little molluscs that invade my garden. For now the horseradish is working as a great decoy plant, and they eat that in preference to most plants, other than my native bush food yam daisies! If only I had space for ducks!

Incidentally, if you’re curiosity hasn’t got the better of you, the picture at the start of the article with the colourful flowers and pretty shaped leaves is not a specifically cultivated garden bed or a intentionally set up photo shot, that’s just  random patch of ground cover under one of my apple trees. Diversity not only takes care of pests, it looks nice too!

In summary, from my observations over the last four years, a food forest can effectively control pests naturally, without human intervention or assistance, and this is solid proof that when a diverse living ecosystem supports a plant, it can form many complex relationships to other plants, soil organisms and beneficial insects, which ultimately increase the plant’s health, vigour and resistance to pests and diseases. In addition, the  microclimates created by other plants create a more hospitable environment for the plant, reducing stress on it and increasing its resilience.

So, no surprises, Geoff Lawton was right all along about the effectiveness of natural pest control in a food forest system, and one thing I’m discovering is that the more I practise real, hands-on permaculture, the more comfortable I feel to push the envelope and venture out of the safe and familiar bounds of conventional practices, and as I do so, the more I discover that what I was taught in my PDC really works. There’s a whole world of discovery to be had for those who are willing to go out there and do it!

Further Reading: