Kate WallHow to rescue and restore a flooded garden

Five years ago, my own garden was waterlogged but not flooded. All around me was flooded. A lovely garden at the end of my street had gone from a delight to a muddy mess. This was my inspiration to do something. I set up a volunteer group and got to helping “floodies” restore their gardens. Assisted by another lady that I met at the local school (which had turned into a temporary flood recovery centre), we co-ordinated volunteer workers, donations of plants, fertiliser, mulch and gardening equipment and got busy.

Totally flooded garden

This is the house and garden that inspired me to rescue flooded gardens. The crepe myrtles and the Poinciana behind them that can be seen here survived, but the understorey of orchids, clivias, subtropicals and flowers largely did not. Without permission we could not go in and work in this garden. The elderly owners never returned and a lot was lost in a once beautiful garden.

The summer of 2011 saw much of Queensland flood, and Brisbane experienced its worst flooding in 40 years. We worked across an area of ten inner Brisbane suburbs, but provided free advice and donations to people as far as Ipswich and Caboolture.

We found that for many, some advice on what to do was all that was needed, others were elderly or overwhelmed or simply just too busy trying to rebuild their homes to touch the garden. For all of them having someone to turn too made an enormous difference to their morale, and to step outside and see new life returning to the garden, instead of mud and weeds, became a turning point in their personal recovery. For many of these people it was not just their gardens which flooded, but homes went under and everything they owned was lost. It was a traumatic time, and I am sure that anyone going through any natural disaster knows exactly what I mean.

The same garden 6 months later. The ctenanthe and palms are fine. The staghorn on the tree is dead, the clivias, begonias and ferns from this garden bed are all gone and the grass tree is barely hanging on, but ultimately didn’t make it. This garden was underwater for less than 48 hours.

The same garden 6 months later. The ctenanthe and palms are fine. The staghorn on the tree is dead, the clivias, begonias and ferns from this garden bed are all gone and the grass tree is barely hanging on, but ultimately didn’t make it. This garden was underwater for less than 48 hours.

We sat in gardens with owners and cried with them at the loss, and then with joy as we were able to donate new plants, mulch away the mud and see the gardens start to flourish again. The Aspley Orchid Society very generously donated some orchids, and this was a real highlight – to be able to visit some of the gardeners who had lost precious orchid collections and to give them some new orchids was very touching.

We were able to do working bees in nearly 100 gardens, and helped so very many more through donations and advice.

Volunteers working to clear the garden of weeds and dead plant matter for an elderly couple, approx. 6 months after the flood. By this time the silt had baked rock hard on top of ground compacted by the flood. Breaking the soil to plant new plants here was challenging!

Volunteers working to clear the garden of weeds and dead plant matter for an elderly couple, approx. 6 months after the flood. By this time the silt had baked rock hard on top of ground compacted by the flood. Breaking the soil to plant new plants here was challenging!

We now know so many others and local gardeners within the community have formed new friendships. This connectedness to our local community, especially to other local gardeners, helps to make us and our gardens more resilient to whatever may come along. For a gardener, as we watch a garden recover, so our spirits recover along with the garden.

Here are my top tips for rescuing and restoring a flooded garden for those gardeners who have watched their gardens flood this season.
These tips relate most specifically to summer flooding in warm to hot climates but much of this will be useful to anyone regardless of climate or time of year.

•  Clean off silt and debris from the leaves so plants can breathe again. This may need rubbing down with soapy water or if the plants are tough enough, even use a high pressure hose;

•  Remove all rotting plant material away from healthy plants to limit the spread of fungal diseases;

•  Depending on how long your garden was under water or water logged, you may have lost a lot of soil biota, so dosing the garden with seaweed solutions is very helpful;

•  Mulching (after seaweeding) is very useful in not only protecting the soil, but also for covering the silt and keeping it moist so that worms can return and incorporate it into the soil. Flood silt will compact to form a hard crust so it is important to either dig it in (not my preferred option) or cover it to keep it moist and allow the worms to do the work for you;

•  Seaweed solutions help promote root growth, and also increase a plants ability to withstand stress conditions – including water logging. Regular repeat doses will be beneficial if you feel your plants are not coping well;

•  Plants that are still showing signs of stress in the weeks and months after could be succumbing to root rot, with Phytophthora being the main culprit, and a treatment with a phosphoric acid based fungicide should be given. Trees in particular can be very slow to show signs of distress and by the time the signs are there it could be too late, so a precautionary treatment of fungicide for trees is a good idea. Fungicide needs to be applied to the soil around the roots. Ensuring the soil has good drainage, added organic matter and a treatment with a seaweed solution or similar with micro-organisms will all help roots to fight off fungal diseases;

•  Soil fertility can be leached during heavy rain and flooding, so applying an organic fertiliser under the mulch can be beneficial;

•  Contamination from raw sewerage was a real issue in the Brisbane 2011 floods. While faecal bacteria can only survive in soil for a few days, other pathogens may also be present. If you suspect sewerage contamination, use gloves and protective clothing when gardening, possibly including a mask, mulch well to allow natural soil biota to do their work, and avoid growing edibles for at least a season after you are sure there is no longer a current source of contamination (eg broken pipes);

If you live downstream from an industrial area and are worried about contamination, you should contact your local EPA for advice regarding what the contamination is likely to be, and how best to treat that contamination. Treatments can vary according to what the contaminant is and how bad the contamination is.

The same garden 2 years after garden recovery (2013). At this stage the soil was still hard but where it had been mulched was teaming with life and full of worms.

The same garden 2 years after garden recovery (2013). At this stage the soil was still hard but where it had been mulched was teaming with life and full of worms.

If you have experienced flooding during winter in the UK or US recently, things will be a little different for you. Much of the above will still apply. The extent of long term damage is often based upon how long the soil is underwater or water logged for.

Plants which are dormant in your cold winters may be fine so long as they are not sitting too long in waterlogged soil. Cold weather and continuing rain will certainly make it very difficult for the soil to dry out. If you can get the waterlogging to subside within days, there is every chance your winter dormant plants will be reasonably unscathed.

Rot is the biggest killer in flooded gardens, and in cooler situations this may be much slower to cause trouble, especially in areas which normally experience somewhat wet winters. Areas which normally have dry winters and have received heavy rain and flooding are the ones most likely to see significant losses in the garden, as these plants will be far more susceptible to rotting during a dormancy period when they would normally be dry.

Leave fertilising until the warm growing season returns, but do not leave the silt layer exposed to set hard if you possibly can avoid doing so.

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Kate Wall

About Kate Wall

Kate has gardened since she was a child. Gardening as a profession came almost by accident - after volunteering to rescue flooded gardens and working in over 100 gardens, she felt her trial by flood had directed her to her true calling, and she has gardened professionally ever since. Kate is primary care giver to approximately 20 gardens concurrently (including her own), in addition to consulting, garden makeovers and creating new gardens. She lives and works in Brisbane, Queensland, and is passionate about gardening to suit our sub-tropical climate.

2 thoughts on “How to rescue and restore a flooded garden

  1. RE: leefieldhouse@rocketmail.com
    Lee Fieldhouse, Islands in the Stream, Oxley Island near Taree
    0429 197 596

    Thanks for a truly great feature Kate.
    “Ensuring the soil has good drainage, added organic matter and a treatment with a seaweed solution or similar with micro-organisms will all help roots to fight off fungal diseases;”
    … yes, exactly, and to that end have only recently become aware of Lee Fieldhouse at Islands in the Stream on Oxley Island near Taree, who has a production of live microbes in liquid form that restores nutrient availability to root systems using the chemical signature from worm spit & castings.

    Seaweed products, yes, and do assist microbial activity in supplying organic nutrient as a microbe starter but having beneficial fungal and bacterial microbes in the top soil is the “floor” enabler that unlocks nutrient to plant life. Can even be used as a foliar treatment or diluted & poured into saucers over night to be absorbed by capillary action into root balls. Using this method, I’ve not suffered a single loss at planting, even in low 40 degree heat .. !!

    I’ve no commercial axe to grind here, just a Designer passing on a good product that might further assist you in your heroic work.

    Kate Wall is a good person

    • Kate Wall on said:

      Hi Peter, thanks for your comment. You are very right about the value and depth of application of seaweed solutions. There are many products available, some even made from aloe vera, and they all offer huge advantages not just in fighting off fungal diseases after flooding but for so many situations – but that is another story in itself!
      This product does certainly sound great, and would be very beneficial in any situation where plants could do with some extra care.

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