All posts by Matt Power

About Matt Power

A member of the Resilience Hub Board, Matt is an environmental journalists, videographer and dedicated gardener. A founding member of the Tiny House Industry Association, he is Editor-In-Chief of Green Builder magazine. He lives and works in Portland.

Urban Leaves: Free, Plentiful, and Laced with Lead

City leaves often contain heavy metals, so compost with care.

A few years ago, I heard Maine farmer Will Bonsall “go off” in praise of leaves as a natural and free form of compost, better, he claims, than almost anything else you can buy in a bag. But he was talking about leaves acquired on or near his rural farm, not the ones raked off of city lawns.

Mixed Blessing. Although rich with nutrients, urban leaves can also be high in lead and aluminum. Source: Chemical Composition of Municipal Leaf Waste and Hand-Collected Urban Leaf Litter

I’ve been using about 100 bags of leaves as compost every season, collected from curbsides around Portland, where the locals conveniently rake it up and stuff it into paper, biodegradable bags.

What could be wrong with free, easy to access (often pre-shredded) leaves? Unfortunately, there’s a catch. (Isn’t there always?)

While reading an obscure book written in 1870 praising the use of “muck” by southern farmers (their term for half-rotted leaf mold), it ocurred to me that use of leaves in rural and urban settings shouldn’t be assumed to be equally virtuous.

The Lead Problem

In many areas of Portland, for example lead levels in soils are hundreds of times higher than “safe” levels, as determined by the EPA. I know this from samples I have had tested. Certain areas are worse than others, of course. Prior to 1978, most homes were painted repeatedly with lead-based coatings. Any house in Portland older than that likely STILL has lead content in the paint, the plumbing or elsewhere.

Lead doesn’t dissipate much on its own, so our soils are heavily afflicted with it. The older and denser the region of town, the higher the likely lead (Pb) content.

Back to my point about using leaves as mulch. Are they safe? Do they pick up heavy metals such as lead?

The answer, according to a study done in New Jersey on municipal leaf mulch, is yes, (unfortunately).

Researchers  found numerous metals in curbside leaves, including lead,  iron and aluminum. They suggest that this occurs because the fallen leaves “become contaminated with urban soil and dust from the road surface through various processes (raking, lawnmower pickup and vacuum) used for litter collection in the yard and at curbside.”

Of the various contaminants, lead is arguably the most concerning. How bad is the potential pollution in city leaves? They apply a standard of 45 Mg/ha, based on tests of sewage sludge–which equates–by my calculation, to about 45 tons of leaf matter spread on 2.5 acres of land.

Break that down to the garden plot level.  An acre is 43,560 sq. ft. If you were only adding this much material to your beds, you would add about 1.21 lbs/sq. ft  of leaf compost per year (108,900 sq. ft, divided by 45 tons/90,000 lbs.=1.21 lbs. per square foot).

Given this level of application, lead levels in your garden would not exceed the EPA rules for “annual pollutant loading rate”–at least for a few years.  In the worst case scenario, with the highest level of lead contamination the researchers found in leaves, an application of this much leaf matter would take 16 years of repeated use to exceed EPA levels.

Don’t get too relaxed, however. If you’re like me, you add significantly more leaf mulch than that to your beds.

Let’s say you have a 4 ft. x 20 ft. garden bed. At the intensity of leaf mulching suggested by the researchers, you would only add 96.8 lbs. of material to the bed (80 ft. x 1.21 lbs/sq. ft.). But I’ve often added many times that much free leaf mulch to my beds at the end of a season, haven’t you? A yard of compost weighs between 1,000 and 1,600 lbs., depending on water content. That means that if I happen to apply what amounts to a yard of highly contaminated (at the worse end of the scale) curbside leaves to my annual beds, I could exceed EPA safety levels for lead in my garden in less than two years. And this assumes that we can trust the EPA guidelines are strict enough, which is a matter of some debate.

What to Do Now?

All of this is incredibly frustrating of course. Human beings somehow seem to turn the most benign sources of natural abundance into new forms of poison. We’re encouraged to buy our way out of the problem, paying exhorbitant amounts for “clean” compost products in 80 lb. bags. What a racket! It’s not unlike what’s happening with our water supplies. We’re forced to either buy bottled water or install an expensive filter if we want to drink clean water.

So let’s not give up on urban leaf compost. We just have to be more strategic in where we obtain it. And also, here’s one caveat: If the leaves will be used in a garden that is strictly ornamental, you’re probably safe to use as much urban leaf material as you like. The lead levels are probably too low to be of concern for pets or casual contact. I would mainly be concerned with gardens used for food production. The details matter. Certain plants, such as berries and fruit trees, for example, are unlikely to draw lead contamination into the fruit. But other plants absorb lead like crazy, especially in their roots. Brassica nigra, or Black Mustard, is a good example. Mustards seem especially good at extracting lead from soils. So are sunflowers.

Where I would take special precautions, however, is with the introduction of urban leaves to  annual gardens where cabbages and leafy greens are grown for consumption.

Here are my suggestions for reducing the risk to your health and your soils, while still using urban leaf compost:

  • Avoid gleaning from the old City. In Portland, for example, I would not use leaves gathered on the West End or Munjoy Hill, nor in Bayside, for that matter. A lot of the debris from the great fire of 1866, for example is buried in Bayside, and these “historic” areas are often toxic wastelands in terms of the lead contamination of the soils.
  • Look for natural lawns. Much as we’d like to see all lawns replaced with permaculture gardens, that’s a long way off. In the meantime, gather leaves from homes with heavy grass cover that doesn’t look like herbicides have been applied. The grass reduces direct contact between leaves and soil.
  • Favor new developments. Scout out new developments  on the urban fringe, where homes were built after 1978. I suspect someone has a map of Portland with an overlay based on the age of the neighborhood. If so, post it here in the comments please.

Sorry to be the bearer of bad tidings about urban leaves. I wouldn’t take them off your list of permaculture resources. Simply be more selective in where you acquire them. Head for the outer suburbs, and be careful about buying your mulch from organizations that use urban leaf compost as a major component of their mix.

Matt Power is a West End resident and board member of The Resilience Hub (resiliencehub.org), a Portland-based organization that brings permaculture and community together. He is also the author of “The Tiny House Tactical Guide,” and Editor-In-Chief of Green Builder Magazine.

Edible Abundance Next to the 7-11 Parking Lot

Three years of strategic planting and coaxing demonstrate that urban food gardens can grow almost anywhere.

If you happened to walk by the 7-11 parking lot at the corner of Dow St. and Congress St. in Portland this fall, you may have seen the evolution of an eye-catching urban garden.

About three years, my partner Melissa and I decided to tackle the only open piece of ground near our house on Dow Street. With permission from the 7-11 owners, we began to systematically apply permaculture strategies to bring life back into soil that looked more like fireplace ashes than dirt. Three previous trees on the spot died long ago, leaving only stumps, and scrub grass and weeds struggled to survive.

This narrow strip of land (mostly hidden by snow at this writing) now includes two healthy apple trees, a pear tree, a blueberry plant, strawberries, along with ample comfrey, several herbs and medicinal plants including yarrow, oregano, thyme, sage and chives. You’ll also find speedwell, daylillies, clover, salvia, and Creeping Charlie as a groundcover.

This garden showcases the power of “permaculture.” We’ve noticed many small pieces of land in the City where harsh chemicals, dog droppings, trash and neglect have damaged soils. We wanted to show that even the worst land may be rejuvenated, if you apply the right techniques and patience.

The process requires a lot of heavy mulching, along with careful planting of different species of plants that assist the trees as they take root. For example, the leafy comfrey plants around the trees are called nitrogen fixers (forgive me if you know all this stuff already). They extract nitrogen from the air and deposit it into the soil, especially if you trim them and let the leaves rot around the trees. Other plants, such as the clover and Creeping Charlie groundcover, keep the soil cooler and allow plants to better respond to drought.

Each year, the amount of work we volunteer in the garden has decreased. We water only about one third as much as we did the first year, and the groundcover is gradually replacing the old scrub grass that was there. We’ve planted sunflowers in the areas that still need work, because they extract heavy metals from the soils, and provide food for birds and squirrels. Later, we’ll replace them with perennial plants like the upper half of the garden. The area is now alive with bees and sparrows again by mid-summer.

We believe a place of peace, beauty and food brings many intangibles to the city. So many cool things have happened since we started the project. Less trash is thrown into the area. People with mental illness sometimes sit among the birds and bees and find a moment’s solace. Older neighbors stop by and ask about the plants and thank us for creating a place they enjoy as they walk home. Someone has put many beautiful painted stones around the trees. We have even had some of the regular alcoholics in the area offer to “guard” the garden and “kill anyone who goes near those trees!” We thanked them for their kind offer and told them that was probably a bit excessive …

This year, our hard work really produced in a tangible way, when the two apple trees actually sprang forth with a couple of hundred delicious apples. Next on the agenda, to identify other properties in the area where magical food forest gardens could appear in coming years, and interest other neighbors in “adopting” a patch of neglected ground.

Matt Power is a West End resident and board member of The Resilience Hub (resiliencehub.org), a Portland-based organization that brings permaculture and community together. He is also the author of “The Tiny House Tactical Guide,” and Editor-In-Chief of Green Builder Magazine.