After the floods: why trees fall and gardens struggle after extreme rain
Cyclone Koji crossed the coast a couple of hours north from where we live, and even though we didn’t get the worst of the winds, there was a lot of destruction around us. Houses flooded, roads damaged, and an incredible amount of water moved through the landscape.
We mainly got massive rain. Close to 500 millimetres over a couple of days, which is a huge amount for gardens, soil, and roads to handle.
When you get rain like that, the soil doesn’t just get wet. It becomes completely full. Everything is saturated, and once that happens, there’s nowhere for the water to go. It just builds and builds.
We had the exact same thing happen a couple of years ago after weeks of heavy rain, and the result was the same then as it is now.
Trees started falling. Other plants struggled, and some died.
Losing trees you thought were solid
One of the hardest ones for me was a beautiful native hibiscus. The photo above shows you where it used to live. There’s now a gap in my canopy along the road, in what was part of my privacy screen. That’s where it stood.
One day it was fine. The next day it had just given way.
And interestingly, the same thing happened again this year. Not another Hibiscus, but three other trees.
We haven’t lost it entirely yet. We’re going to try to save one of them. But I want to be honest upfront. Once trees of that size fall, the chances of full recovery are fairly low. The damage to the root system is often extensive, and big trees are incredibly hard to stabilise again.
This year I lost a grevillea. It was a large one, close to four metres tall, a beautiful Honey Gem – one of my favourite grevilleas of all time. Massive orange flowers that birds and insects absolutely adore.
Seeing that tree lying on its side has been heartbreaking.
It isn’t completely down yet, but it had started leaning badly. I’ve already had to cut off a lot of the lower branches because it was crushing orange trees and other plants nearby. We’re going to try and save it, and I’ll talk more about that later.
And then there’s the one that really hurts.
The Panama berry that fed everything
My giant Panama berry has fallen.
This tree is honestly one of my favourite trees on the property. I planted it in the chicken/food forest garden, and it has been such a provider. It drops these beautiful, sweet little berries for months, feeds the chickens, attracts birds, and provides incredible shade.
It was five, maybe six metres tall.
The whole thing has gone over.
That one I can’t save. It’s simply too big. I’ll have to cut it down and accept the loss, which is gut-wrenching, but sometimes that’s the reality after events like this.
Why big trees fall after heavy rain
You might wonder how such large trees, which you assume must have massive root systems, can suddenly fall over after rain.
The key thing most people don’t realise is that trees don’t rely only on deep roots. A huge amount of their stability comes from wide roots spreading sideways near the surface. When the top layer of soil turns into slurry – basically a thick layer of mud – that sideways bracing disappears.
The tree is suddenly relying almost entirely on whatever roots go downwards, and many trees simply don’t have enough of those to compensate, especially after long dry periods where roots stay shallow.
When soil becomes saturated, the particles separate. Water fills the gaps that normally hold air. And roots need air. They need oxygen to stay alive. When the soil is full of water, the oxygen is pushed out. The fine feeder roots (the ones trees desperately rely on) are the first to suffocate.
That’s the hard part. The tree can look completely healthy while this is happening. The damage is already underway underground. By the time the tree falls, it’s often already too late.
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Rain plus wind is a bad combination
When heavy rain is combined with wind, like during this storm, the problem escalates fast. The rain does the real damage. The wind just speeds the process up.
The soil has already lost its strength, and then the wind catches the canopy and finishes the job. People often blame the wind, but it’s really the waterlogged soil that caused the failure.
Compacted soil makes it worse
A lot of trees have root systems concentrated in the top layers of soil. If that soil is compacted, roots can’t go deeper.
Our soil grows beautiful plants, but it is compacted. We’ve got a decent topsoil layer, and underneath that, heavy clay. When dry, it sets hard. When wet, it swells and becomes unstable. Clay soils make this problem much worse. They turn into swollen masses when wet, then shrink and crack when dry. Roots tend to follow those cracks rather than penetrate deeper.
Interestingly, trees that are watered frequently often develop weaker root systems. They never had to search for water or nutrients. Meanwhile, trees you’ve neglected down the back of the yard (the ones you never watered) often survive better because they were forced to spread and dig deeper.
Why plants go backwards after big rain
You’d think plants would love all this rain. We usually associate rain with growth. But after very heavy rain, many plants actually go backwards.
The soil is soaked, but the roots are suffering from oxygen starvation. Even though they’re wet, they can’t breathe. Roots stop functioning properly. Nutrient uptake slows or stops. Plants can wilt or yellow even though there’s plenty of water.
A lot of fine feeder roots die, and the plant has to regrow them before it can grow above ground again.
Nutrients and microbes take a hit too
Heavy rain can wash out nitrogen and other nutrients, especially in sandy or disturbed soils. Leaves yellow, and people often rush to fertilise.
I recommend waiting.
Adding fertiliser too soon can stress plants further because damaged roots can’t take it up properly. On top of that, many beneficial soil microbes also need oxygen. When soil is waterlogged, they slow down or stop working altogether. Nutrient cycling stalls, and plants temporarily lose their support system.
This isn’t weak plants or trees
When trees fall or plants struggle after rain, it isn’t because they were weak to begin with. It’s almost always a soil issue.
Rain doesn’t cause the problem. It reveals it.
What actually helps long-term
Mulch (affiliate link) makes a massive difference. It stabilises soil, softens the impact of rain, and protects soil structure.
I stopped buying mulch (affiliate link) a few years ago because it became expensive and we’re a long way from town. But I can see now that overall plant health does decline without it, even when you’re doing everything else right.
I try to make my own from fallen leaves and organic matter, but it’s not the same as spreading a hundred bales of sugarcane mulch everywhere.
Structured soil is what you’re aiming for. Not loose, but stable. That comes from organic matter, worms, roots, mulch, and time. Avoid bare soil wherever you can. It might not look tidy, but it’s far better than soil cooking in the sun or sealing over in rain. Groundcovers, self-seeding plants, even weeds are better than bare ground.
Grow plants with different root depths. Trees, shrubs, herbs, groundcovers. Let roots overlap. Let things get a little wild. And try not to water constantly. Water deeply when needed. Let plants search. Tough plants build strong roots.
Can fallen trees be saved?
Sometimes, yes.
If the roots are mostly intact, soil is still attached, and the tree tipped rather than tore, you’ve got a chance, especially with smaller or younger trees. That’s why I’ll try to save the grevillea.
But big trees like my Panama berry? The odds are almost zero.
We tried tying up the native hibiscus last time this happened. It didn’t work. The tree eventually died. Sometimes the kindest thing is to accept the loss and learn from it.
If this has happened to you, you’re not alone. Big rain exposes things we don’t usually see, especially underground.
Let me know if you’ve had trees fall or plants go backwards after heavy rain. I’d love to hear what happened in your garden. And maybe we can share the heartbreak a little!
