Large planters are a dream for any outdoor space. They make room for lush tropical plants, dramatic foliage, even small trees and shrubs — instantly transforming a bare terrace or front entrance into something alive and beautiful.
But there's one thing that catches most people off guard when it's time to plant: how much potting soil a big container actually needs. Good-quality potting mix isn't cheap, and filling a large planter to the brim can quietly turn into a surprisingly expensive project.
Here's the good news: you don't have to fill the whole thing with soil. Most plants only need the top portion of a planter for their roots. The bottom? That's where you can get creative — and save a lot of money in the process.
1. Cardboard boxes and newspaper
Old cardboard and newspaper are one of the most eco-friendly filler options out there. They break down over time, eventually composting right inside the pot and adding a little extra nutrition to the soil above.
Tip: Don't use them in large, intact sheets. Tear or shred them into smaller pieces first. Big unbroken pieces absorb too much water and can starve your plant's roots of moisture.
Best for: Plants you repot regularly — roughly every one to two years — since the material will break down and need replacing around the same time anyway.
2. Empty cans and plastic bottles
Aluminium cans and plastic bottles are excellent space-fillers that cost you nothing. Line the bottom of your planter with them and you'll use significantly less soil to reach the right planting depth.
Tip: Always keep the caps on plastic bottles. The trapped air inside prevents them from being crushed under the weight of the soil above.
How to do it: Fill roughly a quarter to a third of the planter with bottles or cans. Then lay a piece of landscape fabric (or fine mesh) on top — this stops the soil from sifting down between the gaps while still allowing water and roots to move freely.
3. Garden clippings, twigs, and dry leaves
If you have a garden, you already have everything you need. Pine cones, dry leaves, small branches, and woody clippings make a completely free and surprisingly effective filler. As they decompose, they even enrich the soil above with extra nutrients.
Best for: Plants that get repotted every few years. The organic material will gradually compact and break down — but conveniently, that's also about when you'd want to refresh the potting soil anyway.
4. Old bricks and broken terracotta pieces
Broken clay pots and old bricks do double duty as planter filler. They take up space efficiently, but more importantly, they add serious weight to the bottom of the pot — which means your planter won't tip over in strong wind, even when it's holding a large, top-heavy plant.
Tip: Place your planter in its final position before you start filling it with bricks — it'll be nearly impossible to move once it's loaded. Also make sure the bricks don't block the drainage holes at the bottom of the pot.
5. Old plastic nursery pots
Those black plastic pots your plants came in from the garden centre? Don't throw them away. Flip them upside down and stack them in the bottom of your large planter — they're perfect as lightweight, reusable filler.
Tip: Pour the potting soil in slowly and carefully so it settles into the gaps between the pots without shifting them out of place.
Why it works: Upturned nursery pots create air pockets at the base of the planter, which improves aeration and drainage. Just make sure there's still enough depth above them for your plant's root system to develop properly.
Know your plant's roots before you start
Most plants root to a depth of around 15 to 30 centimetres. Before you choose a filler, look up how deep your specific plant's roots typically grow. The upper portion of the planter needs to provide that full depth of quality soil — everything below that can safely be replaced with any of the alternatives above.
How to fill a large planter — step by step
Check drainage first. Make sure your planter has drainage holes. Without them, water will pool at the bottom and rot the roots. If there are no holes, drill some — or if that's not possible, add a thick layer of charcoal or crushed shells at the very bottom to help with drainage.
Add your filler. Layer your chosen material into the bottom of the planter. Depending on how shallow your plant's roots are, this can fill up to half the pot.
Top up with potting soil. Fill the remaining space with good-quality, nutrient-rich potting mix.
Plant and water. Place your plant, firm the soil gently around the roots, and give it a thorough watering to help everything settle.
