Tree Soil Decompaction, Air Spades & Improved Soil Biology Saves Trees

Trees Need Air At Their Roots & Air Spades Can Be Used For Root Zone Aeration aka Arbor Aeration Which Promotes Healthy Roots Soil Biology.

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The storm that crossed the UK in 1987 uprooted millions of trees. The lucky trees, though hit hard by the storm, actually survived and led to air spades being invented. But the storm was so severe that it literally rocked the trees in the soil. In some cases the trees were literally uprooted only to fall back into place as the storm subsided. Others rocked so hard that it was like the lived through a series of mini earthquakes with the soil around their roots being shaken, fractured and decompacted.

But what happened next was unexpected and lead to a new branch of arboriculture science and the formation of specialist arboriculture businesses that now focus on soil decompaction and soil health.

And this lead to the invention of air spades!

The 1987 Storm Impact on Trees Lead to Air Spades

Those trees that hadn’t keeled right over, but were left in the ground, or in some cases substantially in the soil, went on to thrive. Within a few months they were doing better than ever before. It was as if they had been given a tonic. And in this case the tonic was a shot of air to the roots.

The thing is plants need oxygen at their roots. If the soil is capped or otherwise compacted they get starved or air at their roots and eventually die. Many trees suffer restricted growth due to a lack of air at their roots. It is the single factor that holds therm back.

Any tree that gets a lot of traffic over its root zone is potentially threatened. People walking in parks, may not weigh much individually but in aggregate their weight compacts the soil over the roots, especially in wet weather. And this can kill a tree.

Trees near to roads suffer even more. They have layer of tarmac between the roots and the air above and can suffer badly. Ditto where they are planted in paved areas. The lack of air at the roots can kill, or severely stunt, trees.

And this is where the first thoughts of air spades started. As a cure for soil compaction around trees.

Soil Compaction In Vegetable Gardens

Soil Profile, soil horizons, Original: Wilsonbiggs Vector: EssensStrassen, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

I’ve seen evidence of this in veg gardens and even on my market garden. When I grew large numbers of lettuce, by the field full, there was evidence of the restrictive results of air not reaching the roots of plants. Often, after planting tens of thousands ion lettuce in the field they would rapidly grow until we had excessively heavy rain. Heavy rain would hammer so hard on the soil surface that it could form a “cap” or crust on the soil surface. It was extremely thin but was impermeable to air and the plants would soon suffer. The answer was to hoe between the rows and I used a “Bean tractor” to break the cap and let the air back in.

I’ve experimented with hoeing all the rows bar one to see if there was much difference. The results are stunning. Often the unhide rows. lacking air getting to the roots, would take weeks more to reach maturity. In the worse cases they actually died.

It’s exactly the same as for the trees. But with trees the scale is much bigger as the compaction often goes inches or even feet in to the soil.

Soil Compaction Impact

With soil compaction the bulk density of the soil increases. This leads to the inability for water and air penetration, leading to anaerobic conditions as well as water logging in some cases.

With compacted soils, and a lack of soil porosity, the roots struggle to penetrate the soil and nutrient deficiencies are soon apparent. Drought is also evident, even in wet weather. Drought not because of the a lack of f rain, but because the rain cannot penetrate the soil.

At the same time as this the soil biota, the living parts of the soil, start to die out. The fungi, bacteria and small life forms die. And life leaves the soil.

Soil Decompaction Methods That Led To Air Spades

Whereas I could hoe my lettuce that isn’t possible under a large mature tree. So the arboriculturist has to find another method. They use “air spades”.

Air spades are devices that are used to penetrate the soil with soil probe and pump compressed air into the soil. The purpose isn’t to supply the air. It is to lessen the soil. It’s rather similar to the fracking process used to extract gas and oil from shale. But don’t confuse the two. This isn’t going to bring gas or oil to the surface. Gas and oil fracking is done at depth. Tree soil decompaction is done in the top few feet of soil.

Soil Decompaction Equipment

Commercial soil decompaction equipment, aka air spades, basically consist of an air compressor, and pipework leading to a soil probe of some sort. Sometimes the equipment is portable and is used as a backpack. But the bigger systems are too big to be highly portable and need extensive lengths of pipe work from the compressor to the soil probes.

Back Filling After Air Spading

Where appropriate various infill substrates can be added to the soil after air spading. Biochar, compost, feeds or whatever is required can be dropped in to the loosened soil either by gravity or via the air gun with a reduced air flow rate.

How To Decompact Garden Soils

In the garden we can work on a smaller scale. We don’t even need an air spade. A fork can sometimes be used where the problem is not too severe. Insert the fork into the soil and move the handle backwards and forwards in an arc. this will lessen the soil in the top few inches, maybe down to a foot deep. Repeat across the plot, inserting the fork ever 6-12 inches.

On lawns a spiking or hollow tine machine can be used. the latter removes a core of soil which cane replaced by sand, compost or whatever you choose. Just spread the filler on the soil and brush in.

On a larger scale, where a tractor can be used in a garden, a subsoiler can be used. This is like a subterranean plough that pulls a torpedo shaped blade through the soil and fractures it. Even on my market garden, with its light soil, I would do this very couple of years. Both up and down and across the field to ensure every square foot was treated.

If an air spade, aka Air Pick is required they can be hired. Some utility companies now use them when digging around sensitive pipes, live mains etc.

What About Soil compaction In No Dig Gardens?

In No Dig gardens there is unlikely to be a soil compaction issue. We tend to keep off the soil far more, and it is also more open and resilient due to the penetration of roots and worms taking the compost down.

Do Worms And Grass Roots Decompact Soil

To an extent yes. In the No dig garden they worms and any root penetration helps soil structure and hence air penetration. But, if your garden is already compacted it’s going to take time. Spreading organic matter on the surface and letting the worms take it down will work but it’ll take a few years.