The short answer is no; timber edging does not last, and we cover why below. As you will see, there are a few variables to consider if planning to use wooden garden edging both at ground level and in raised garden beds.
We have a few spots in the yard where we have metal raised garden beds and other areas with ground-level gardens that are edged with various materials. One site has hardwood 4×4 inch lengths separating the garden from the lawn.
This hardwood is Grey Stringy-bark, and for those not familiar with this timber, it is an Australian eucalypt that is very hard and long-lasting above ground.
A day or so back, we had a good patch of rain, which triggered a flush of mushrooms to pop up from this hardwood garden edging and got us thinking about how long this wood would last us.
We suspect this flush of fugal activity is an indicator for us to begin the process of planning replacements for this edging.
The mushrooms are a simple indicator and a quiet reminder that everything is always in a state of decay. The only thing to be sorted out is the timeframe we have to work with that item.
Garden bed edging made from wood or timber can generally decay quite fast in many locations because of the natural processes that break down wood into soil. Keep this in mind as you decide what material to make the garden bed or garden edging from.
We live in the wet tropics of northeast Australia, where fallen wood in the rainforest can rot back into the soil in a short couple of years. While wood in a desert environment will take decades to break down.
The reason for this time difference is the available moisture where the wood is located. Gardens are often watered, and so do the math. For alternative materials for garden edging, “what is the safest material for organic raised bed gardening?” is recommended.
What woods are suitable for garden edging?
Natural timbers that are hard are the best for any garden edging purpose because when the wood ends up rotting away, the garden plants can utilize the wood components or nutrients.
Hardwoods have a longer life than softwood, and some timbers have natural protection against rot; however, this natural protection will only last for so long before the wood starts to break down. Every piece of wood will rot in the end.
A major plus for using wood, even if rot shortens the garden edging life, is wood’s ability to keep the soil cooler than other materials.
As with most things in life, there are payoffs and losses to consider, and cooler soil temps are definitely a plus. “Does the soil in metal raised garden beds get hot?” explains it all for you with data from an actual test we conducted.
What causes wooden garden bed edging to rot?
In a moist environment where the wood is in contact with the soil, timber edging will begin to rot quite quickly. The micro-organisms in the soil are the instigators for the wood to rot, and this is a natural process that has been happening for ages.
Both bacteria and fungi are involved in the breakdown process, and it cannot be stopped completely, so it should be planned for at the beginning of a garden design.
The typical garden bed regularly watered is one of the harshest environments that wood can be in. It is silly for us to think that the garden edging will last. Every
Does treated wood last longer than hardwood edging?
Not in our experience, but this is a debatable subject because there is an industry built around selling the idea that chemicals can keep wood rot at bay.
While it may help for a few short seasons, the end result is the wood will rot, and there may be harmful chemicals released into the soil in the garden from the decaying wood. Hardwood is our preference if timber is to be used as edging.
The material choice is not as important when the wood is used at the ground level and is used primarily as a mowing strip or similar. The construction material choice becomes far more critical when raised garden beds are being built.
Replacing the sides of a raised garden bed that holds a cubic meter or yard of soil is not something you want to do every few years, so keep this in mind.
Is treated wood safe to grow vegetables near?
It is unlikely that the chemicals used to treat wood are safe or beneficial for you because they are designed to kill bacteria and fungi in the soil.
These same life forms allow us to grow food organically. If we use chemically treated wood to prolong the life of a piece of wood by killing any biology near that wood, the plants will be the ones to lose out here.
This then opens the door to using chemical fertilizers to feed the plants because the soil is a little short on natural life forms that feed the plants naturally for us.
We don’t know the long-term effects of the chemicals as they relate to growing food. Still, as we rely on biological processes in our gardens, we prefer to approach them cautiously.
We see the process of wood being turned into soil as a good thing, and we design around these natural processes where we can. We even try to use these same processes to our benefit.
Can hardwood be sealed to preserve it for longer?
Yes, hardwood can be sealed to help preserve the wood from rot. Beeswax can be used in some situations, but the end result is that the wood will eventually succumb and be returned to the soil.
If you wish to use beeswax, there are recipes where vegetable oil and crushed charcoal blended with beeswax are applied to the wood before the garden edging is used.
If beeswax in a block is rubbed on the wood surface and then melted into the wood with a hot air blower, it can give some protection for a while.
How long is unknown yet, and will depend on the wood, the soil, and how well you apply the beeswax to the wood surfaces. Open-grained woods will allow more wax to penetrate than hardwood will.
The best thing here is that it is entirely natural and is safe for soil and vegetable growing.
The simple thing to remember with any wood in contact with moist soil is that it will rot. While there are chemical treatments and others that are natural, the result is that the timber garden edging will require replacing at some point.
Other materials are worth considering as you plan the garden edges or raised garden beds.
Article by Tim Blanch for TheTropicalHomestead.com. He is a qualified Permaculture designer.