Are Charcoal Ashes Good for Plants? The Pros and Cons

Charcoal ashes are a common backyard gardening dilemma – what do you do with the leftover ash after a barbecue? Can you use charcoal ash for plants, or should you avoid it? In this detailed guide, we’ll examine the pros and cons to find out if charcoal ashes are good for plants or not

Charcoal ash is simply the powdery grey residue left over after burning charcoal. There are two main types of charcoal used for barbecuing – lump charcoal and charcoal briquettes

Lump charcoal is pure charcoal made from pieces of wood burnt in a low oxygen environment. Briquettes are made by compressing charcoal dust and filler ingredients into uniform shapes.

The key factor determining whether charcoal ash is good for plants is avoiding any chemical additives. Natural lump charcoal or untreated briquettes produce a safe charcoal ash. But many modern briquettes contain additional lighter fluids, binders, fillers, etc. The ash from chemically-treated briquettes should not be used in gardens.

So can charcoal ash go on plants? Let’s examine the potential benefits and drawbacks.

The Potential Benefits of Charcoal Ash for Plants

When sourced properly, charcoal ash offers some potential benefits:

• Nutrients: Charcoal ash contains minerals like calcium, potassium, and phosphorus which are beneficial for plants. The potassium in particular helps strengthen plants and aids in disease resistance.

• Soil pH: Charcoal ash has an alkaline pH, so sprinkling it around acid-loving plants can help balance overly acidic soil. It contains compounds that gradually raise pH over time.

• Pest Control: The lime in charcoal ash can kill or deter certain insects and pests. Either apply dry ash around plants or mix with water to make a pesticide spray.

• Moisture Retention: Charcoal ash particles can help aerate soil and retain moisture when added to potting mixes and garden beds.

• Frost Protection: Applying a heavy layer of charcoal ash around plants can help protect them from light frosts, thanks to ash’s effect on freezing points.

Potential Drawbacks of Using Charcoal Ash

However, there are also some potential drawbacks to keep in mind:

• Soil pH: While charcoal ash raises pH in acidic soil, it can harm plants that prefer acidic conditions (like blueberries) by making the soil too alkaline.

• Salt Buildup: Excessive charcoal ash application can lead to a dangerous salt buildup in soil over time. This damages plant health.

• Toxicity: Ash from chemically-treated briquettes may contain toxic additives. Ash can also concentrate heavy metals from the original charcoal source.

• Nitrogen Depletion: Too much potassium from ash can interfere with plants’ nitrogen uptake, leading to deficiency.

• Dust Issues: Charcoal ash is a fine dust that irritates lungs if inhaled. Caution is needed when handling and applying ash.

How to Use Charcoal Ash in Gardens

When using charcoal ash around plants, proper application is crucial:

• Test your soil’s pH first to identify any need for raising pH. Avoid applying to already alkaline soil.

• Source ash from untreated, chemical-free charcoal only. No briquettes.

• Apply lightly – no more than 1-2 tbsp per square foot. Mix well into soil.

• Water plants after applying ash to help dissolve minerals and salts.

• Add extra nitrogen fertilizer to compensate for ash’s potassium.

• Wear a mask when handling ash to avoid breathing dust.

• Sprinkle around acid-loving plants only if soil tests show a critical need. Monitor soil pH.

• Till ash deeply into soil – don’t leave sitting on top.

• Use ash sparingly in potting mixes – 5-10% by volume max.

Some examples of plants that may benefit from light charcoal ash application include tomatoes, peppers, roses, fruit trees, lawns, and certain shrubs.

Avoid heavy application around blueberry bushes, azaleas, rhododendrons, camellias, and conifers.

An Important Note on Other Types of Ash

While this article focuses on charcoal ash, two other common backyard ash sources are also sometimes used:

Wood Ash: This alkaline byproduct of burning firewood contains many nutrients but is best applied lightly and sparingly like charcoal ash. Avoid ash from chemically-treated wood.

Paper Ash: Most paper ash is chemically similar to wood ash, but ash from paper with dyes, coatings, etc. is not garden-safe. Plain newspaper ash or unbleached paper ash should be fine in moderation.