A Garden Myth that I needed to Dig a little Deeper on!
Recently, someone shared a quote from The Informed Gardener by Professor Linda Chalker-Scott, which argued that compost should be added only on top of the planting hole, not inside, and that planting holes should be as deep as the root ball but twice as wide.
I appreciate that this advice comes with good intentions, but as with most things in gardening, the truth is more nuanced.
Let’s break this down and explore what’s really going on below the surface.
How deep and wide should a planting hole be?
Linda Chalker-Scott recommends digging the hole only as deep as the root system and twice as wide.
This is generally good advice: planting too deep can cause settling and lead to burying the crown, which leads to rot. A wider hole encourages lateral root growth and helps roots establish in compacted or heavy soils.
When this works
In well-prepared soils or areas where compaction is minimal, this method encourages roots to spread into the native soil.
When this might fall short
In soils that are heavily compacted, hydrophobic, or of poor structure (like urban fill or degraded sites), simply making the hole wider without addressing the surrounding soil quality won’t necessarily help roots establish well.
Should you amend the planting hole at all?
The claim is that you should never amend the planting hole “in any way” and only backfill with native soil. The logic is to avoid creating a “pot effect” where roots stay in the nutrient-rich pocket and don’t venture into the surrounding soil.
There is truth here
If you fill the hole with soft, rich soil or lots of organic matter, especially in clay soils, roots can circle in the hole or fail to move into denser surrounding soils. Water can also perch at the boundary between two very different soil textures, leading to waterlogging at the root zone.
But context matters
In very poor soils, think subsoil, building rubble, or extremely sandy soils, some incorporation of well-aged compost or organic matter into the backfill can help create a healthier root zone. The key is blending the amendment with the native soil to avoid creating sharp boundaries.
Is compost in the planting hole always a bad idea?
The supporter’s comment suggested compost should only go on top as a mulch. While top-dressing with compost is great for feeding soil life and improving surface structure, a blanket ban on incorporating organic matter at planting doesn’t always hold up.
Top-dressing is fantastic
It feeds worms and microbes, protects soil from erosion, and slowly improves structure.
But moderate incorporation can be beneficial
Particularly in soils low in organic matter or with poor biological activity. It’s not about filling the hole with pure compost, but blending small amounts with native soil can jump-start root zone health.
Are we “spoiling” the plant with rich compost in the hole?
There’s a common belief that putting compost in the hole spoils the plant and encourages roots to stay put. But plants don’t get “lazy”, roots grow where water, air, and nutrients are available.
If surrounding soils are inhospitable, no amount of compost on top will change that. In these cases, improving the soil beyond the hole (via broad soil prep or blending amendments) is key.
Does this advice apply everywhere?
It’s important to note this recommendation came from Washington State, a climate with very different soils and conditions from, say, much of Australia. What works well in the Pacific Northwest may not directly translate to South East Queensland, where soils, rainfall, and temperatures differ.
The take-home message
There is no one-size-fits-all rule in gardening. The best planting method depends on your soil, plant type, and climate.
In the end, soil health and structure are what truly support thriving plants and that often means looking beyond the hole.
I’d also add that the organic matter you’re adding has a shelf life. It breaks down within a relatively short period of time, so ultimately you’re giving your plant a good start but that’s all. Long-term soil health comes from ongoing care, not just what you put in the hole at planting.
So next time you hear a planting rule, take a moment to look at your own soil, your climate, and your garden’s needs. Gardening myths often have a seed of truth but real success comes from understanding the full story.