Your Plants Eat Dirt… Sort Of

If you’ve ever looked at your potted plant and wondered how it absorbs all its nutrients and water, well, you’re not alone.

The truth is, plants don’t chew through soil or sip it up like a smoothie. They pull in nutrients dissolved in water through their roots — but they can’t do it alone. Hidden in every healthy pot of soil is a microscopic workforce of bacteria, fungi, and other tiny life forms turning raw materials into plant food.

In a garden bed, this soil life hums along naturally. But in a pot? Things get a little trickier. The closed environment of a planter means nutrients wash away faster, microbes face harsher conditions, and you (the plant parent) have a much bigger role to play in keeping that underground dinner party running.

This weeks blog aims to cover just how plants draw up nutrients from the soil, the  role microbes play, and why your potted plants might need some extra help to keep their microscopic caterers happy.

The Nutrient Highway: From Soil to Stem

Plants need a mix of macronutrients (like nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur) and micronutrients (like iron, zinc, manganese, copper, and boron) to grow, repair, and stay healthy. (side note, this is why we're always waxxing on about the importance of a complete fertiliser.) These nutrients are almost always taken up in dissolved form — meaning they’re carried to the roots in water.

Here’s the quick science of how it works:

1. Roots explore the soil with thousands of fine root hairs, increasing surface area.
2. Water in the soil dissolves minerals and organic compounds, creating a nutrient soup.
3. Root membranes absorb nutrients through a mix of passive flow (osmosis) and active transport (where the plant spends energy to pull specific ions in).
4. Xylem tubes inside the plant carry that nutrient-rich water upward, supplying leaves, stems, flowers, and fruit.

Sounds straightforward, but there’s a catch: many nutrients in soil aren’t actually in a plant-ready form. Nitrogen, for example, might be locked away in organic matter or unavailable chemical forms. That’s where microbes come in.

Meet the Microbial Middlemen

Healthy soil — whether in a forest floor or a pot on your balcony — is alive. In fact, a single teaspoon of healthy garden soil can contain more microbes than there are humans on Earth.

In the wild, this living community turns dead leaves, organic matter, and minerals into plant-accessible nutrients. In pots, they still play that role — if we give them a fighting chance.

Bacteria: The Chemical Converters

• Some bacteria, called decomposers, break down complex organic matter into simpler compounds plants can use.
• Nitrogen-fixing bacteria can take nitrogen from the air and convert it into ammonium or nitrate, forms plants can absorb.
• Nitrifying bacteria convert ammonium into nitrate — another vital nitrogen source.

Without these bacteria, most nitrogen in your potting mix would be locked away, useless to your plants.

Fungi: The Root Extenders

• The real rockstars in potted plant nutrition are mycorrhizal fungi.
• These fungi form partnerships with plant roots, growing fine filaments (hyphae) that extend far beyond the root zone.
• They can access pockets of phosphorus, zinc, and copper the roots can’t reach.
• In exchange, the plant sends sugars (produced through photosynthesis) down to feed the fungi.

Think of it like hiring a personal shopper who not only brings the groceries to your door but also finds the rare ingredients you’d never locate yourself.

Other Soil Life

Protozoa, nematodes, and microarthropods also join the nutrient cycle, feeding on bacteria and fungi, and in the process, releasing nutrients in plant-available forms. It’s a busy, interconnected food web — all happening in a space smaller than your fist if you’re growing in a pot.

Why Potted Plants Have It Tougher

In the natural world, soil is constantly replenished with organic matter (leaf litter, animal droppings, dead plants) and colonised by an endless parade of microbes.

In a pot, conditions are very different:

• Nutrient leaching: Every time you water, some dissolved nutrients wash out the bottom of the pot. Without replenishment, the soil becomes poorer over time.
• Limited biodiversity: Potting mixes are often sterile when sold to prevent pests and diseases from hitchhiking. That means no microbial head start.
• No natural top-up: There’s no steady fall of leaves and organic debris in a pot unless you add it yourself.
• Environmental stress: Pots heat up and dry out faster, which can stress or kill delicate microbial communities.

If you’ve ever wondered why a plant can struggle in the same mix after a year or two — even if you water it well — you’ve seen this problem in action.

Feeding the Soil Life in Your Pots

If you want your plants to thrive long-term, you need to think about feeding both the plant and the microbes in its pot. Here’s how:

1. Choose Microbe-Friendly Fertilisers

Not all plant food is created equal.

• Synthetic salt-based fertilisers deliver nutrients quickly and more effectively, but can harm beneficial microbes if overused.
• Organic or biologically active fertilisers (like our Soil and Microbe Booster) tend to be gentler, while also providing carbon sources microbes use as fuel.

When you feed microbes, they, in turn, feed your plant — it’s the ultimate win-win.

2. Add Microbial Inoculants

If your potting mix started out sterile, you can introduce life yourself.

• Mycorrhizal fungi inoculants can be dusted on roots at planting.
• Liquid microbial concentrates or compost teas can be watered in to seed beneficial bacteria.
• An organic frass-based slow release fertiliser can be used seasonally - we've got you covered here

Just remember: adding microbes without also giving them organic matter to feed on is like inviting guests over and not offering any snacks.

3. Keep Soil Moist (But Not Soggy)

Microbes need water to move and function, but they also need oxygen. Saturated, airless soil can suffocate them.

• Water deeply, but allow the top layer to dry slightly between waterings.
• Avoid letting pots sit in saucers of stagnant water.

4. Top-Dress with Organic Matter

Adding a layer of compost, worm castings, or even shredded leaves on top of your pot helps:

• Provide slow-release nutrients.
• Shelter microbes from temperature swings.
• Feed the entire soil food web as it breaks down.

In other words, it’s like delivering a care package to your pot’s underground tenants.

5. Avoid Microbe-Killing Practices

• Minimise heavy chemical pesticide use. 
• Avoid boiling water or harsh cleaning products in pots you plan to reuse for planting.
• If you must sterilise soil (e.g., for pest control), be ready to reintroduce microbial life after.

A Living System in Miniature

Think of your potted plant not as a lonely houseplant, but as the visible tip of an entire living system. In that small volume of soil:

• Roots reach and exchange.
• Bacteria convert and cycle nutrients.
• Fungi weave microscopic highways.
• Tiny predators keep populations in check.

When you support the microbial side of that system, your plant gains access to more nutrients, withstands stress better, and grows with the kind of vibrance you notice every time you walk past it.

The Takeaway

Your plant’s roots are clever, but they’re not magicians. Without the microbial workforce in the soil, many of the nutrients in your potting mix stay locked away.

By using microbe-friendly fertilisers, adding inoculants, and creating conditions where soil life can thrive, you’re not just feeding a plant — you’re sustaining a whole ecosystem in miniature. And in the world of potted plants, that’s the secret to long-term health and beauty.

So next time you water or feed your plants, picture the microscopic feast you’re setting in motion. In your pots, microbes are the quiet heroes turning dirt into dinner — and your plants couldn’t live without them.