Potash vs Biochar: What’s the Difference and Which is Better for Your Garden?

One of the most common questions I get from customers is: What’s the difference between potash and biochar? Both are used to improve soil, but that’s where the similarities end. Understanding their roles, and their limitations can help you make better choices for your garden.

What is Potash?

Potash is a potassium-rich substance, usually made from wood ash or mined minerals. It’s widely used as a quick-release garden fertiliser because potassium is essential for plant health, it helps plants grow stronger stems, resist pests, and produce more flowers or fruit.

However, potash isn’t without its downsides.

The Drawbacks of Potash:

• Short-term impact: Potash dissolves quickly in water, meaning much of it can be lost before plants get a chance to absorb it.

• Soil imbalances: Overuse can cause an excess of potassium, which may block the uptake of other vital nutrients like magnesium and calcium.

• Raises soil pH: Wood ash-based potash is highly alkaline and can make soils too basic, harming plants that prefer slightly acidic conditions.

• No soil structure improvement: Potash doesn’t help with water retention, microbial activity, or overall soil health.

So, while potash has its place in correcting nutrient deficiencies, it’s not a holistic or sustainable solution.

What is Biochar?

Biochar is a type of charcoal made by heating organic material (like wood or crop waste) in a low-oxygen environment. It’s not a fertiliser on its own, but it’s one of the best tools available for long-term soil improvement.

When charged (or "inoculated") with compost or natural fertiliser, biochar acts as a nutrient sponge. It holds onto nutrients and water, reduces leaching, and provides a permanent home for beneficial microbes in the soil.

Why Biochar is a Better Long-Term Solution:

• Improves soil structure and water-holding capacity

• Reduces fertiliser waste by retaining nutrients in the root zone

• Boosts microbial life, supporting long-term soil fertility

• Balances soil pH without extreme swings

• Stays in the soil for decades, unlike soluble fertilisers

Biochar doesn’t just feed the plant, it feeds the soil ecosystem. Over time, this leads to healthier plants, fewer inputs, and more sustainable growing.

Final Thoughts

Potash and biochar play very different roles in the garden. Potash is a short-term nutrient fix with some risks if overused. Biochar, on the other hand, is a long-term investment in your soil’s health and productivity.

If you’re looking to build resilient soil, retain nutrients, and reduce fertiliser use, inoculated biochar is the smarter, more sustainable choice.