Planting depth has always been a very simple concept in gardening and horticulture. You simply put the plant in at the depth as it was in its pot and you can’t go wrong. Planting any deeper is heresy, because it will die very quickly from root rot or collar rot. This has always been the conventional wisdom, that I, myself, have spread for many years.
However, I did a story a couple of years ago for Gardening Australia on a subject called long stem planting, where plants were put in up to a metre deep. You get some long tubestock, a deep hole is drilled and you virtually just bury the plant alive, up to a metre deep. It seems like horticultural heresy, but my experience with this technique suggests that it does really work.
The long stemmed planting technique can be found on the internet. If you search for “Bill Hicks” and “long-stem planting” you’ll find a
whole lot of research that this very dedicated environmentalist has done on this technique. It’s something he pioneered, as a technique for stabilising river banks, in the Hunter Valley in particular. Being concerned about the use of willow trees to stabilise river banks, and then those willow trees going feral, Bill Hicks posed the question, “why not use indigenous native plants?” He was told that they would wash away in the first flood on those river banks so he suggested planting them a bit deeper. This idea met with all the usual objections, but over a 20 year period, Bill has been planting things up to a metre deep and the results have been nothing short of astonishing. Not only to the majority of plants put in much deeper survive, but they actually thrive, growing at a faster rate and they are also much more stable.
Now why would it be that planting things much deeper than normal gives a much better result? A few points have arisen out of Bill Hick’s work.
1. When you plant more deeply, the rootball of the new transplanted potted plant goes in at a level that’s better insulated from the soil surface. The rootball is usually in the top few centimetres of the soil, and if that dries out, the whole plant is at risk unless you can water it regularly. If it’s planted more deeply, it’s down in the subsoil, insulated, so it doesn’t dry out as readily.
2. It’s apparent from research that most plants that are planted deeply have the capacity to form a new root system along the buried stem, giving it a big advantage in terms of being able to access water and nutrients from a much greater depth in the soil profile.
I have personally observed many planted trees that were deep planted perform better.
Are there any exceptions to the deep planting rule? Anything with a clumping habit is excluded, like an agapanthus or a dianella, that has its growing points at ground level; if they’re planted a metre deep they’d never make it to the top! But anything that has an elongated stem, and especially plants that strike well from cuttings, it’s possible. Over the past two years I’ve experimented with this technique, and I’ve found it to work for a very wide range of plants, both native and exotic.
I’d like you to take some small plants home that you could afford to lose, and do a little experiment at your place with deep planting. The plants don’t have to be a metre long to be successful like Bill Hick’s long-stem planting, as that’s a more specialised thing for erosion control, where obviously the deeper the root system the better. But in the garden I’ve found that taking a plant that’s 10 or 15 centimetres high and planting it so that 70% or so is below ground level, does give you tremendous growth advantages.
To summarise, deep planting works because the plants establish better and over time they form a much more extensive root system that gives the new plants a competitive advantage.
There are a couple of conditions:
1. The stems do need to be elongated and the more easily they form adventitious roots like when they’re struck from cuttings, the better result you’ll get with that species.
2. The other important thing is oxygen in the soil. If you have a very heavy clay soil that’s constantly waterlogged then I’d be wary of using the deep planting technique.
So – have a go! And please let me know about your experiments with deep planting – both your successes and failures!