Charcoal as a Soil Amendment

This article first appeared in The Times-Herald Record on Saturday, May 11, 2019 in the Home & Garden section.

By Joe Gregoire, Orange County Master Gardener, Cornell Cooperative Extension Orange County

I’ve heard that adding carbon to the soil by mixing in charcoal is good for plants.  Is this correct?  Jessica from Monroe

burning wood in a fireplaceGreat question, Jessica.  And as I’ve just recently cleaned out my fireplace from the winter and wondered if I could use the ash in my garden, I’ve done a little research on the topic that I’ll share with you here.

There is a long history to the practice of adding ash and charcoal to soil and is a proven method of soil improvement.  The pre-Columbian Amazonian peoples developed an understanding of the importance of soil carbon as they worked to meet their agricultural needs in their hot and humid rain forest environment.  Their warm, wet climate created conditions in which soil organisms quickly decomposed organic material – that was then absorbed into the rapidly growing rainforest flora.  When rainforests are cleared and plowed, this soil is quickly depleted of soil carbon and susceptible to erosion, making food production difficult to sustain on the same land for more than a few years.  However, archeologists have found that ancient Amazonian cropland contains large deposits of dark, rich soil called Terra Preta that was made by these ancient farmers between 2,500 to 4,000 years ago.  This Terra Preta contains high amounts of charcoal created through the process of pyrolysis (burning organic material in high heat and low oxygen) which preserves up to 50% of the carbon vs. converting it into CO2 gas through complete combustion.  Pyrolysis produces a very porous and stable form of organic matter through physically and chemically altering the composition of the biomass being burned.

pile of charcoal bitsUniversity studies have shown that adding charcoal (also called Biochar) to soil increases the soil’s water-holding capacity, reduces soil density, improves soil structure, and has been proven to reduce soil nutrient leaching and increase crop growth. Pre-packaged biochar can be purchased from retailers today or can be made at home by buying or building a biochar kiln for home use.  Many low-cost designs can be found online and enable the conversion of biomass (wood) into charcoal to amend the soil.  Biochar can be produced from a variety of materials – trimmings from woodland and yard maintenance, agricultural waste like corn stalks, and purpose grown biomass such as bamboo. The pH and composition of the biochar that is produced is directly linked to the material used to produce the biochar, so if making your own, be sure to avoid contaminants such as treated or painted lumber.

Biochar has many properties that have potential to enhance soil fertility and is a highly stable form of organic matter, as the 4,000 year-old Terra Preta demonstrates.  Organic matter in soil is important for retaining moisture and building soil structure through aggregation, which also provides pore space for drainage.  Soil organisms depend on this balance of air and water in soil to survive and thrive. With increased soil life comes increased soil nutrients to feed your plants.

If you have access to fireplace ash, this can be another ready source of charcoal and other beneficial soil amendments.  Wood ash is a good source of potassium, lime, and micronutrients (which are taken up from the deep roots of hardwood trees used for firewood, such as oak and maple).  It is best to add ash to the compost pile rather than directly to the garden, as the high concentration of lime can alter soil pH and may burn sensitive plants.  The alkaline nature of wood ash can also have a neutralizing effect on compost, as the decomposing materials in a compost pile can become somewhat acidic.  Do not use ash from a charcoal grill, as this ash may contain chemical residue from lighter fluid.

Because of the alkaline nature of wood ash, avoid using it around acid-loving plants such as azaleas, rhododendrons, and blueberries.  Wood ash can also be used as a natural repellent for pests such as snails and slugs who will resist crossing a line of wood ash laid around their favorite plants (the salts in wood ash are an irritant to these soft-bodied pests).  The wood ash needs to be reapplied after a rain or watering to remain effective.

Carbon in the soil is the key to soil life.  Growing plants exude carbon into the soil through their roots in the form of sugars produced through photosynthesis.  These exudates attract and feed beneficial bacterial, fungi and other microorganisms that live and die in the area surrounding plant roots, providing plants with nutrients they need to be healthy.  Our addition of carbon to the soil, in the form of charcoal, can provide additional material for this symbiotic relationship to play out in our garden soil.  And in doing so, we can play an important role in removing carbon from the air and returning it to the soil through our everyday love of gardening.

Click on the graphic below to learn more about soil health!

How can you improve your soil health? A link to an interactive infographic that explores soil management practices, soil helath benifits and soil organsim functions. (Sustainable Agriculture Research & Education - SARE).
An Interactive Exploration of Soil Health and How to Improve It

To learn more about the benefits of biochar and current research on biochar visit:

Biochar – Cornell University

Biochar and Compost Facilities – Cornell University

Terra Preta de Indio – Cornell University

To learn more about using wood ash as a soil amendment check out:

Best Management Practices for Wood Ash as Agricultural Soil Amendment – University of Georgia

Guide to Using Wood Ash as an Agricultural Soil Amendment – University of New Hampshire

Wood ashes can benefit gardens and lawns – Oregon State University

Native Bees

Which Native Bee Is That?

By Susan I., Sparrowbush Senior Master Gardener

This article appeared in the June 2019 Issue of Gardening in Orange County. Click here to subscribe!

Even though there are almost 400 species of native bees in New York, these bees usually zoom right under our radar.  They work and nest on our property yet are often unrecognized and unnoticed (let alone understood) as the crucial pollinators of our flowers and food crops.  Most natives are not aggressive and sting only if provoked. Unfortunately, they often get mistaken for bellicose wasps or hornets and, sadly, are obliterated.

Bees evolved from insect-devouring wasps 100 million years ago.  Bees are wasps that went vegetarian.  They evolved away from hunting insects to bee species adapted for efficiently gathering more nutritious pollen to feed their larvae.

Three-fourths of our native Orange County bees are ground-nesters that dig tunnels or take over beetle or mouse burrows.  The rest nest above ground in straw-like stems, twigs, stonewalls, or in hollowed-out deadwood.  Most of them are solitary – meaning the queens build, gather, provision, and care for their nests all alone.  Males often look like a smaller version of their queens.

Close up of a bumble bee on an orange flower
Bombus pensylvanicus

BumblebeesBombus

Closely related to foreign honeybees, these charismatic bees have an iconic stocky, round shape and small wings that defy the aerodynamics of lift and drag.  The distinctive flat shiny spot on female’s back legs is surrounded by hairs to form a pollen basket.  They use this basket to transport pollen wetted with nectar, but, unlike the honeybee, they never stockpile it.  Bumblebees live in ground dwellings, not hives, and are distinguishable by their waist-less anatomy covered in black and yellow hair, especially on the abdomen.  Queens make their nests in animal tunnels or tussock grasses.  A queen will travel up to a mile for pollen to feed her young, usually referred to as her brood. The more flowers available for pollen, the larger her brood.  Colonies last only one season – compelling swift, and prodigious pollen collection, 15 times that of the honey bee.  Males leave the nest and do not normally return, spending their time feeding on nectar and trying to mate.

Bumblebees are flower generalists and are the preeminent pollinators of tomatoes.  To do this, they clutch the tomato flower and vibrate their abdomen to shake out the pollen found inside.

Pinned mining bee specimen
Andrena nigrae

Mining Bees

These strong bees dig deep ground-nests leaving volcano-shaped mounds in sand, clay, grass or under fallen leaves.  Often their nests are aggregated and are easily spotted when females are orientating themselves to the “door” of their nest by flying in larger and larger figure eights around it.  Males can also be seen swarming around the complex, but instead of orientating themselves, they are looking for an opportunity to mate.  Although one hole leads to many underground “apartments”, each queen lives separately with her brood. The communities’ females exhibit an orderly morning exodus one at a time.

Our most numerous native bees, miner bees fly only from late April to July. They emerge to the surface at around 40 – 50 °F to absorb the sun’s warming rays, and take of flying when temperatures reach 50 – 60 °F.  They fly fast and are valued for pollinating early morning flowers that bloom before honey bees wake up.

Close-up of a carpenter bee on a wooden fence
Xylocopa virginica

Carpenter BeesXylocopa virginica

Common in Orange County, carpenter bees are the largest of our native bees.  Females resemble bumblebees – only they are larger and have a hairless shiny black abdomen. Males’ faces are yellow while females’ faces are black.  They are named “carpenter bees” because they cut precise round galleries for nests inside sound, undecayed soft wood.  They avoid wood covered with paint or bark and have been known to cut their galleries in fence posts, wooden benches and houses leaving what some would consider unsightly holes and stains.  Males are attracted to sudden movements and conspicuously hover closely to people or in front of nests.  They also engage in aggressive territorial battles for mating opportunities, but fortunately for us males cannot sting. Females can sting, but only do so when molested.  Adults emerge during the summer and fall and can live for up to three years.  Females will sometimes cohabitate with their daughters and, unlike most native bees, carpenter bees will reuse old nests. Carpenter bees are beneficial and important pollinators, especially of open-faced flowers.

Mason bee on board with
Mason bee apartment
Mason Bees

New York’s several species of Mason bees choose above ground nesting sites in preexisting cavities such as twigs, hollow stems, and beetle burrows.  Child and pet-friendly Mason bees are far too busy to be aggressive. They only sting as a last resort, and the venom they release is very mild.  If you’re allergic to honeybees, this solitary, docile pollinating rock star is easy to keep and a great alternative.  They cross-pollinate a wide variety of trees and plants instead of focusing on stripping pollen and nectar from one location.  You can help protect them in winter by leaving standing hollow-stemmed plants.

Close-up of a leaf cutting bee on a yellow flower
Osmia ribifloris

Leaf Cutter Bees

The female leaf cutter bee makes small circular cuts in living or dried leaves or petals.  She curls them up to carry back and line her nest.  Attracting these gentle yet vigorous pollinators requires growing plants with thin-walled leaves, such as roses, hostas, peas, and lilacs.  Because they build their nests near one another and are 15 times more valuable as pollinators than honey bees, they aid farms and gardens where lots of bees are needed. Unlike carpenter bees, solitary leaf cutter bees cause no damage to structures, because they lay their eggs in existing holes.

They are more round, cigar- or submarine-shaped than other bees and carry collected pollen on their abdomen.  Distinguishable from honeybees, they have no brown/yellow stripes on their abdomen.

Close up of a sweat be on a white petal that tuns red at the center of the flower
Agapostemon virscens

Sweat Bees

Sweat bees make up for their minute size with their incredible numbers and are among the most abundant and commonly seen bees in North America.  They are attracted to the proteins, moisture and salt on sweaty arms, legs, and necks.  Don’t swat!  Females will sting if brushed against or agitated, and they will release pheromones attracting more bees.

Up to twenty-four solitary females dig deep burrows in banks or on flat or sloping soil – they then share the entrance into the nest.  They are most active in late spring and summer.  Sweat bees have short tongues which makes it difficult for them to extract nectar from deep flowers.  For this reason, they are attracted to open-face flowers.

FYI – Wasps 

Paper wasp resting on top of its nest
European paper wasp – Polistes dominula

Although wasps are usually considered pests, adult wasps are considered beneficial since they capture insects for their developing larvae.  They also feed on sweet nectar (and can annoy picnics in late summer by scavenging on human food).

yellow jacket feeding on rabbiteye blueberry
Yellow jacket

Some of the more common wasps found in our area are yellow jackets, bald-faced hornets, and paper wasps.  Yellow jackets usually build their nests in the ground or in voids found in buildings.  Their colonies last only one season and nests are not reused.  Bald-faced hornets are actually not true wasps, but a type of yellow jacket.  They are large black and white wasps that make the grayish papery, pear-shaped hives (mistakenly illustrated as Winnie the Pooh’s “honey bee hive”) found hanging from trees or shrubs.  Bald-face hornets also do not reuse their nests.  Like the bald-faced hornets, paper wasps also make papery nests, but their nests have open combs.

Bald-faced hornet nest 20 feet in a Maple tree 9 inches in diameter
Bald-faced hornet nest

Just remember that wasps are considered beneficial, so unless their nests are in an undesirable place, they should be left alone. One way to dissuade wasps from nesting near your home is to use an imitation wasp nest. (These can be crocheted or purchased.)  As visual creatures, when they see another “wasp” nest in the area they assume it’s another competitor and do not build there.

It’s clear that bees are good for our gardens and as long as our gardens provide reliable pollen and nectar sources, our gardens are good for the bees. Unfortunately our native bees are in decline due to loss of habitat, residual pesticides in their food sources, pathogens, mites and diseases.  Our first step in helping them is understanding them and their ways.  Protect their livelihood by proliferating their only food source – flowers – which renew and sustain them year-after year.  Here are a few other things that you can do to help protect the bees:

  • plant flowers in swaths
  • remember that although modified, doubled-petaled cultivars are ascetically pleasing to the eye, they have less nectar than native cultivars of the same flower
  • choose diverse flowers, preferably natives species
  • intersperse decorative flowers among vegetables
  • allow some of your herbs bolt, producing flowers
  • minimize your use of neonicotinoid pesticides which move systemically through the plant into plant pollen and nectar and can weaken bees’ immune systems.

Flower Power!

More flowers = Higher bee numbers!

In the bargain, humans get free pollinating labor assuring healthy vegetation and reliable fresh foods – and we get to revel in Nature’s door-prize of life – the magnificent, ravishing, inestimable flower.

Squash bee resting on a yellow flower petal
Squash bee – Peponapis sp.

For more information about Wild Bees of New York visit Cornell’s Pollinator Website (https://pollinator.cals.cornell.edu/wild-bees-new-york/).