One of our Lab members, Carolyn, has been fighting an uphill battle (literally) with her food forest in Celaya, Guanajuato, Mexico, for years.

Trees dying, ants taking over, native varieties that "everyone grows" struggling and failing - despite doing everything right: building soil, mulching, drip irrigation, composting. She's lost over a dozen fruit trees in the past few years - pomegranates, avocados, citrus - species that thrive everywhere else in the region. At one point, she told me she was ready to give up on the food forest entirely.

I'm sharing her story because chemical drift from neighboring properties is a problem many of us face or might face at some point - and the solution is simple and easy to apply on your own land.

Hidden chemical drift

Carolyn's food forest sits downslope from a large grass lawn area on the same 100-hectare property. That lawn is used as a party/event venue and is regularly treated with chemical fertilizers and pesticides.

Here's what was happening:

1. Subsurface chemical runoff from the treated lawn was draining directly into her food forest soil, poisoning the root zone of her fruit trees
2. Ants were being poisoned out of the lawn area and migrating en masse into her gardens, creating severe pest pressure
3. Surface runoff during rain and irrigation carried additional chemicals downhill

This explained her current challenges. Why native pomegranates and avocados that thrive everywhere else in the region kept dying after a few years. Why pest pressure was relentless despite organic management. Why years of soil building never seemed to "stick."

The breakthrough wasn't a new technique - it was identifying the hidden root cause that was sabotaging all her other efforts: the chemical drift.

Interception ditch + bioremediation

The fix is straightforward: intercept the contaminated flow before it reaches the food forest.

Carolyn dug an interception channel between the lawn area and her garden:

• 11 meters long (36 feet) (spanning the full flow path)
• 1 meter wide (3.3 feet)
• ~70 to 80 cm deep (~2.5 feet)

This captures both subsurface and surface runoff before it enters the food forest.

The physics of capturing surface runoff is obvious - the rain hits the ground, runs downhill, and goes into the interception ditch (hint: that’s why it’s called interception). But also, a huge amount of water moves below the surface, through the soil itself.

When the lawn gets irrigated, or it rains, water soaks into the soil and moves downhill through the upper layers - typically the top 30–60 cm (12–24 inches). This is called shallow subsurface flow. If the soil has been treated with fertilizers and pesticides, those chemicals dissolve into the water, soak into the ground, and travel underground.

In Carolyn's case, the treated lawn sits upslope from her food forest. Every time the lawn is watered, or it rains, contaminated soil water migrates downhill into her food forest's root zone - invisibly, underground.

So when you dig a channel in that contaminated water flow path, you create an open void in the soil where the contaminated water seeps out. Water always takes the easiest path - and an open channel is easier to flow into than solid soil.

Even without a slope, this interception ditch would still work.

The deeper the ditch, the more subsurface flow you capture. At 70 to 80 cm (2.5 feet) deep, you're intercepting water well below the typical chemical treatment zone - which concentrates in the top 30–60 cm (12–24 inches) - giving you a solid safety margin.

Planting the ditch

The interception ditch also serves as a living filter. We’ll be planting it with species chosen specifically for Celaya's 8-month dry season.

Top edge (drier zone):

• Vetiver grass - Drought-tolerant once established, handles wet/dry cycles, roots go 3–4 meters deep, salt-tolerant, heat-tolerant. Widely available in Mexico.
• Moringa - Very drought-tolerant, fast-growing, deep roots. Also, bioremediates heavy metals.

Bottom of ditch (wetter zone):

• Vetiver - Handles both wet and dry conditions, stabilizes the base, and filters water that pools.

Now, there is one more step that most people skip: you must harvest and remove the biomass from the property.

The plants absorb contaminants into their tissues. If you let them grow, die, and decompose in place, the chemicals get released back into the soil. Skip this step, and you're just recycling the poison through your own system.

So, the correct process:

1. Plants grow and absorb contaminants
2. Periodically harvest above-ground biomass (trim vetiver every 2–3 months during the growing season, cut moringa 2–3× per year)
3. Remove that biomass from the site entirely - do NOT compost it anywhere on your property
4. New growth continues absorbing

This is how you actually extract pollutants from the system over time. The ditch + plants do the filtering. Harvesting and removal complete the cleanup.

Look uphill

So…if your trees are struggling and you've "tried everything" - look uphill. Look at what your neighbors are doing. Look at what's happening on other parts of your property.

Sometimes the problem isn't your soil, your water, or your technique. It's what's flowing into your system from somewhere else.

A simple interception channel with the right plants can be the difference between years of frustration and a food forest that finally thrives.

Carolyn's ditch has been in the ground for a few weeks now - we'll report back on how the food forest responds over the coming months. But the logic is sound: stop the contamination at the source, and give the soil a chance to recover.

Have you dealt with something similar on your property? Hit reply and tell me about it. I read every one.

Talk soon,

-William