It’s been over a year since we started our quest to achieve the design intent.
In a few of these articles I have briefly touched on the troubles we face when it comes to creating gardens and establishing ecologies within a construction project. Being surrounded by various trades using tools that can damage our work, along with materials that can be toxic to the ecology we are creating, is quite a challenge. Given most of the building-trades services are pressured with time constraints, our challenges can easily evolve into frustrations when their negligence, ignorance or sadly, sheer apathy requires us to make good on preparing planting areas, repair the damage to existing plants or replace the plants altogether.
In addition to the challenges nature throws upon us, we’re also faced with numerous difficulties which are often induced by us and our related trades.
So let’s crack open the can of issues to get a deeper understanding of what they are, what they do and what we can do to avoid them.
There’s a few, so we’ll need to make them the focus of the next few articles.
Compaction is probably the most common condition and most damaging to the success of the landscape asset. No amount of cunning plant selection can properly solve the problem.
Basically, if a plant’s roots can’t grow into the surrounding soil, the soil might as well not be there. The more the soil particles are compressed, the less pore space we have between these particles. Less pore space means less space for air, water and roots to move through. As air and water can’t move through the soil, the area naturally becomes poorly drained.
So compaction can both keep too much water in the soil by encouraging poor drainage, or keep water out by preventing water from infiltrating the soil in the first place.
Although nothing likes to live in compacted soil, builders love it, landscapers need it for structures and horticulturists should detest it. Basically, by compacting or not alleviating the compaction, we’re ruining the opportunity for the plants to achieve the design intent and us to showcase an attractive landscape asset on our portfolio.
So how do we avoid compacting the soil?
First, stay off it! Especially when it’s wet.
Continual foot and wheel traffic is the biggest contributor. Back and forth over the same area continually compresses the ground beneath. The more it’s compressed, the more air is pushed out, the more the fragile structure is broken down and squeezed together.
Although skid steers and mini loaders are a great help to hasten a landscape project by ferrying materials here and there, they are also the greatest contributors to destroying soil structure.
Looking beyond construction sites, compaction occurs throughout established gardens as well.
Here’s a familiar scenario: the team is working at the back of the Smith’s garden, taking tools, materials and waste back and forth from one end to the other.
How does the front lawn look at the end of the first day?
It’s beginning to discolour and the signs of foot traffic are already evident. A genuine effort to make the Smith’s back garden look terrific has been at the cost of retarding growth in the front garden.
Ground protection is what’s needed.
Remember the suggestion I made last year about using particle flooring boards? $50 buys your site 3.6 metres of ground protection from continual foot and wheelbarrow traffic. It’s even cheaper if you buy damaged boards. Better still, invest in sheets of 19mm plywood. I rip 1200 widths down to 600mm and get 4.8 metres of convenient ground or lawn protection that can last well over a year. The sheets are in a size that’s easy for one person to shift around the site, making the WHS-compliant.
High-density polyethylene ground or bog matts are worthy investments to protect the soil from all levels of compaction. Although they’re heavy and cumbersome, they allow access to areas safely and with much less impact.
Keep in mind if you’re using black matts in full sun to protect a lawn, the matts will heat up and burn the grass beneath.
With any ground protection over lawn, just remember to lift them at knock off so the turf can breathe and access light. Yellow rectangles on the Smith’s lawn are easily avoided by lifting or shifting the boards or matts daily.
With thought and simple planning, protecting lawns and soil from traffic is easily avoided and delivers a duty of care.
You will find having a load of 2400 x 600mm ply sheets on hand will be one of the simplest yet greatest assets to your firm. They’re brilliant for preparing and laying turf, they can protect driveways when dumping bulk materials, they make barrowing over rough ground so much easier and will enable you to keep drier feet during another La Niña summer.
The list of benefits goes on, but I’m digressing.
Although it’s easier said than done, compaction can be reduced by avoiding working the soil when it’s very wet. The process of digging or using cultivating equipment on wet soil ruins the structure by breaking down the crumbs or aggregates of soil. Crumbs or aggregates of soil often resemble the gap-graded sands we covered in our last chat. Lots of particles of different sizes and shapes make for a profile that doesn’t settle into one tight mass.
Digging into wet clay- and silt-based soils also creates a situation similar to compaction.
Shovels tend to polish or smear the surface of planting holes. Using augers and excavators for planting can be very problematic as well. Anytime when we smear the surface of a clay- or silt-based soil with a tool, we are creating a problem called ‘sidewall compaction’. Essentially the smoothed surface that’s created by sliding a shovel, an excavator bucket or auger over it prevents water, air and roots from moving through the smooth interface.
If you’re using equipment that’s polishing or smearing the surfaces of your planting hole it’s important to scuff or break up the polished surface. Spending some of the time you’ve just saved by roughing up the polished or smeared surfaces will help restore conditions better suited to the movement of air and water and assist roots to penetrate through the compacted interface.
If the soil is so wet that the sides of the hole won’t rough up, then it’s far too wet to plant. You’ll be doing the landscape asset a disservice. The plants will surely struggle to establish and grow consistently.
It’s often too wet for bricklayers, concreters and renderers to work, but why do we think it’s not too wet for gardeners to plant?
We know what practices cause compaction and we know how to avoid it. So how do we identify it?
A quick and easy way to test for soil compaction is to use a wire flag as a probe. When the soil is moist to the point of field capacity, hold the wire at the flag end and push the wire part of the flag into the soil until the wire wants to bend. If the wire is pushed to a depth of 300mm or more, the soil isn’t compacted and in good condition. If the wire goes into the soil to a depth of between 150mm and 300mm without bending, the soil condition is fair.
However, if the wire starts bending at a soil depth of less than 100mm, then you’ve got compaction problems.
It’s best to test multiple spots onsite and avoid obstacles like roots, stones and irrigation poly pipe. Lawn areas require at least 100mm of uncompacted soil, whereas gardens need a minimum depth of 300mm. Remember the soil needs to be moist when you’re doing this.
Alleviating compaction can be as hard as the soil itself. Despite this, I strongly urge you not to ignore it as it will greatly affect the look, hinder the performance and encourage diseases.
Next time, we’ll discuss how to rectify compaction.