Your Garden Bed Tub Volume

Use this table to work out how much potting mix you will need. It is worth buying a little extra, because the mix settles over the first few weeks.

Fill It Right to the Top

Fill your Corrogarden all the way up. Potting mix always settles once it has been watered in and has had a little time, so a tub filled to the brim on day one will drop down a few centimetres within a week or two. That is completely normal. Give each layer a light water as you go to help it settle, and plan to top the bed up with a fresh bag of mix at the start of each growing season. A full tub gives your plants the most room for their roots and holds moisture more evenly.

The Breather Holes: A Built In Design Feature

You will notice a row of holes along the sides of your Corrogarden, as well as the drainage holes. These do two important jobs for your plants.

1. They let the roots breathe. Roots need air just as much as they need water. The side holes let oxygen reach right into the root zone, which keeps the roots healthy and active. Plants get their growth from sunlight, water and nutrients, but none of that works properly if the roots are starved of air.

2. They air prune the roots for you. This is the clever part. In a normal sealed pot, roots grow out until they hit the wall, then keep circling round and round. Over time they wind into a tangled, choked mass. This is what gardeners call "root bound", and it slowly strangles the plant, leaving it sickly and unproductive.

Your Corrogarden works differently. When a root grows out and reaches one of the breather holes, the tip meets the open air and gently stops growing. Instead of carrying on in a circle, the plant responds by pushing out lots of new, smaller side roots further back. The payoff is a dense, fibrous network of feeder roots rather than a few long circling ones.

That matters because:

• Better feeding and watering. A bushy, fibrous root system has far more surface area, so the plant draws up water and nutrients much more efficiently.
• No more root bound plants. The circling and strangling problem simply does not get a chance to start, so your plants keep performing season after season.
• Stronger, healthier growth overall. More working roots means a stronger plant above the soil too.

In other words, the holes are doing some of the gardening for you, around the clock, for free.

What to Fill It With: Potting Mix, Not Soil

This is the single most important choice you will make, so it is worth getting right.

A Corrogarden is a container, just a large one. Think of it the same way you would think of a big pot on a patio. Whatever its size, it follows the rules of container gardening, and the first rule of container gardening is simple: garden soil does not belong in a container.

Here is why. Garden soil (the stuff you dig from the ground, or buy as topsoil) is heavy and dense. Out in the open that is fine, because there is endless space around it for water to drain and air to reach the roots. But seal that same soil inside a container and it behaves completely differently. It packs down into a solid block that roots struggle to push through, and it holds onto water like a sponge that never quite dries out. The air pockets fill with water, the roots can no longer breathe, and the plant slowly drowns or rots from the roots up.

Potting mix is the opposite. It is a light blend made on purpose for containers, full of air pockets that let roots breathe and let excess water drain straight through. It stays loose and fluffy instead of compacting down.

This is not just our opinion. Horticulturists, university extension services and gardening bodies are remarkably united on the point: garden soil should never be used on its own in pots, tubs or containers, because it compacts and waterlogs. It is one of the most common reasons a container garden fails.

One more reason, specific to your bed. On top of the gardening problems above, there is a practical one. A Corrogarden is designed and built around the weight of potting mix, not soil. Soil is far heavier than mix to begin with, and it gets heavier still once it soaks up water and refuses to drain. A tub packed with that wet, dense load puts real strain on the walls and base, and over time that can stress or damage the tub. So filling with soil works against you twice over. It harms your plants, and it overloads a bed that was never built to carry it.

Our recommendation: fill your Corrogarden with a good quality potting mix. If you would rather not cart bags around yourself, we offer a Potting Mix Fill Service where we deliver and fill it for you, sized to your exact tub. You will find it linked on this page.

FAQ: Can I Use Soil?

Short answer: please don't. A Corrogarden is a container, and garden soil does not work in containers. It packs down hard and stays waterlogged, which suffocates the roots and is the most common cause of container plants failing. Soil is also much heavier than potting mix, especially once it is wet, and the tub was built around the weight of mix, not soil, so soil can strain and damage it over time. Use a good quality potting mix instead and your plants, and your bed, will be far happier.