April 16, 2025

Are Fire Pit Ashes Good for Plants? Here’s the Dirty Truth

Got a garden and a fire table? You might be sitting on gardening gold. Fire pit ashes aren't just dusty leftovers—they can actually give your plants a natural boost. But before you go sprinkling them like fairy dust, there are a few things you need to know.

Let’s dig in.

Potential Benefits of Fire Pit Ashes for Plants

You’ve just enjoyed a cosy evening around the fire table. The embers are out, the drinks are done, and what’s left behind? A pile of grey ash. Most of us think, “Bin it.” But hold on—your garden might be craving exactly that.

Fire pit ashes can be brilliant when used the right way.

Nutrient Provision

Let’s start with the good stuff—what’s actually in the ash?

Potassium for Plant Growth

Plants need potassium like we need a good cuppa in the morning. It helps them grow strong, fight off disease, and produce better flowers and fruit. Ash from hardwoods like oak is loaded with it.

Think of it as a natural fertiliser—minus the faff and expense.

Calcium for Cell Structure

Just like calcium keeps our bones strong, it keeps plant cells sturdy too. This is especially helpful for fruit trees and roses, which need a strong framework to thrive.

Sprinkle a small amount around the base, and you’re giving your plants a mini spa treatment.

Other Beneficial Minerals

Ash doesn’t stop there. It often contains magnesium (great for chlorophyll), phosphorus, and a mix of trace minerals like zinc and iron.

Basically, it’s nature’s slow-release multi-vitamin for soil.

pH Adjustment

This is where ash becomes a secret weapon for gardeners battling acidic soil.

How Ashes Raise Soil pH

Wood ash is alkaline. So, if your soil is on the sour side, a bit of ash can help tip the balance and make nutrients more available.

But this isn’t a case of “more is better.” We’ll get to that shortly.

Good for Plants Preferring Alkaline Conditions

Not every plant will thank you for ash, but plenty do. Lavender, cabbage, kale, beetroot, and other brassicas thrive in slightly alkaline soil.

Give them a dusting, and you’ll likely see happier leaves and sturdier stems.

Pest Deterrence

Here’s a nifty trick: ash doubles as a natural pest repellent.

Potential to Deter Slugs and Snails

Slugs and snails hate crawling over dry, gritty surfaces. A light ring of ash around vulnerable plants can keep them at bay—no pellets required.

It’s simple, cheap, and surprisingly effective.

Risks and Considerations When Using Fire Pit Ashes for Plants

Of course, even the best intentions can go sideways. Ash isn’t a cure-all—and it can cause trouble if misused.

Let’s explore the risks before your garden ends up looking like a disaster zone.

Over-Alkalisation

This one catches a lot of people out.

Danger of Making Soil Too Alkaline

Ash is alkaline by nature, and too much of it can turn your soil chalky. That might block nutrient uptake and slow down plant growth.

If in doubt, test your soil first. A £5 pH kit can save you a £50 replant.

Harm to Acid-Loving Plants

Got blueberries, rhododendrons, or camellias? Keep ash far away.

These acid-loving plants will sulk—or worse—if you mess with their preferred pH.

Salt Buildup

Another common issue is salt accumulation.

Potential to Harm Plants with High Salt Content

Ash can contain salts that build up over time. In small doses, it’s fine. But go overboard and you’ll burn your plants’ roots and ruin the soil structure.

Especially dangerous in pots and raised beds with limited drainage.

Contamination

Not all ash is created equal.

Risks from Treated Wood or Other Contaminants

Ash from treated, painted, or glued wood (think pallets, MDF, or old furniture) may contain toxic chemicals. These can harm your plants—and potentially you, if you’re growing edibles.

Importance of Using Clean Ashes

Always burn untreated hardwood. No coal, no paper, no paint. Just logs.

That way, your garden gets the good stuff—minus the risk.

How to Use Fire Pit Ashes Safely for Plants

Now that we’ve covered the highs and lows, here’s how to use fire pit ash safely and effectively.

Soil Testing

Before you do anything, find out what your soil actually needs.

Importance of Knowing Your Soil's pH

Buy a basic test kit. If your soil’s already alkaline, skip the ash. If it’s acidic, you might have found your new secret weapon.

Knowing your numbers takes the guesswork out of gardening.

Application Guidelines

This is where things get precise.

Recommended Amounts to Avoid Over-Application

Stick to around 5–10 grams per square metre. That’s about a tablespoon, lightly spread. For larger gardens, 5–10 pounds per 1,000 square feet is the upper safe limit.

Avoid dumping it all in one spot—your plants will thank you.

Type of Ashes

The source matters more than you think.

Using Only Hardwood Ashes

Hardwood produces nutrient-rich ash with fewer resins. Softwood is okay but not ideal.

Stick with oak, maple, beech or ash (yes, the tree—it’s not a pun, promise).

Avoiding Ashes from Treated Wood or Coal

This one’s worth repeating: no treated timber, painted scraps, or coal. Ever.

Composting

If you’re still unsure, composting is a safe middle ground.

Benefits of Composting Ashes Before Use

Mix small amounts of ash into your compost heap. It’ll balance pH, add minerals, and blend into the organic matter beautifully.

Just don’t go overboard—your compost should still look like, well, compost.

Conclusion

So—are fire pit ashes good for plants? In short: yes, but only when used thoughtfully.

Done right, wood ash can be a cost-effective, eco-friendly boost for your garden. It nourishes your soil, keeps pests away, and helps strike the perfect pH balance.

But like any good thing, moderation is key.

Think of fire pit ash as your garden’s seasoning—not the main course. Sprinkle wisely, test regularly, and keep it clean.

And next time you cosy up beside the fire table, know that what’s left behind might just be the start of your garden’s glow-up.