Flood Damaged Gardens

By Pam Thoday, Wartook, Vic.

Many of us have had our gardens saturated by water in the past few months, Pam has some advice for remediating the soil and saving the plants.

There has been unpredictable weather in many parts of Australia over the past 12 months, with some areas still being impacted by flood waters. While many of us were lucky enough not to be under a metre of water or more, we have still been left with gardens damaged by waterlogging and soil compaction.

As you will have noticed, some plants have a higher tolerance to waterlogged soils than others. Desert and Mediterranean plants tend not to cope. In most cases the standing water causes their hair roots to rot away, and the impact is noticed when hot weather starts and the plant simply can’t take up water through those roots. Some trees can continue to function for months on stored water and nutrient, but will ultimately die. It is heartbreaking!

Many people I’m in contact with have lost cherry, apricot and plum trees, while some remaining trees are easily stressed by heat, indicating that they have insufficient hair roots. It may help to prune back stressed trees to reduce the transpiration or loss of water through leaves. Yates sells an anti-rot product that may also assist when sprayed on foliage.

We hoped that some plants would reshoot; a kiwi fruit vine is struggling back, but most were dead when we cut them back or dug them out.

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Review your needs and replant if required. I prefer to buy bare-rooted fruit trees as I can see their root development and they seem to transplant better. We will be making some mounds in the orchard, adding plenty of loam and compost and planting new cherry trees about

20cm above natural ground level. While their roots will still penetrate the natural soil, a mat of hair roots should sit above the water table despite waterlogging.

When preparing the soil to replant, either dig out the stump or cut at ground level and replant nearby and leave the wood to rot, then make sure to dig over the area to at least two spade depths. If the ground smells anaerobic, or like sulphur, leave it to be exposed to UV light and turn a few times to kill bacteria. If not, or after a week, add new soil, compost and potting mix to raise the level.

In winter, plant into your mounds, making sure any graft unions are well clear of soil level. I recommend mulching well and ensuring that these new trees receive ample water, such as drip irrigation, over that first summer as they will be at a higher risk of drying out. When adding mulch keep an area clear of the lower bark to discourage root rot. We cut the top and bottom from large 4lt olive oil tins and cut along one side. This wraps around the trunk leaving a gap and can be removed when the tree has grown.

For existing damaged trees, consider digging swales above them to direct water around the main root area. We are planning some largescale earthworks to channel water away from the orchard area in wet winters, with sluice gates that can be added to retain summer rainfall. Oh the joys of future proofing and its constant modifications! Seaweed emulsion will also assist roots to build immunity to root rot.

In the ornamental garden we removed many dead plants, cutting back those with dead centres in the hope that they will reshoot and bush out. Fortunately we had already propagated many new plants from our garden and decided to remove some badly damaged plants and start again. This enabled us to raise the most affected garden beds by bringing in layers of soil, potting mix and compost. We replanted about 8cm above ground level and re-mulched the beds ready for summer. It felt crazy watering in the new plants after so many months of rain, but nearly all survived the few very hot weeks.

The only bonus from this is that it has enabled as to reassess our plantings and focus on those that we really need, or change the layout to better suit our needs. Some choices are affected by what we experienced, for example English lavenders mainly survived, while those fairy cultivars from Italian lavender were most affected.

Having removed the plant graveyard, I’m past being depressed and have just ordered a big shipment of subtropical plants which will require further earthworks and soil care to ensure their success.

For those who had serious flooding where water sat for weeks or months, my heart goes out to you! All that I’ve written still applies but you may consider resiting your plantings in accordance to where you observed water to flow, and making some earthworks to redirect water away from certain areas.

If planting an orchard, be mindful that some plants enjoy periodic flooding, like grapes and berries, some love water as long as they have good drainage, such as citrus and pomme fruit, apples, pears etc, and some hate waterlogging, including cherries, kiwifruit, avocados and apricots.

F uture F orecast

We have reviewed our climate change forecast to include the implications of both longer and hotter heat waves and prolonged rain events, as expected from a hotter climate. I have plantings in several different areas to hedge my bets and hope that some areas will survive whatever gets thrown our way.

We built a large greenhouse last year, so will use some of that space to increase the growing period. We can germinate seeds earlier and plant out more advanced seedlings, and this year I may consider digging up some plants and growing them in large tubs to ensure we get a crop of eggplants and chillis before they are cold affected.

Raised garden beds for herbs and vegetables are generally less likely to be affected by flooding, and aquatic plantings obviously don’t get damaged by water, but are affected by the prolonged cold nights. Many plants only set flowers within a window of temperature range, so even those not in waterlogged areas will have found production reduced this year with the persistent cold temperatures overnight. For future years, having a removable cover over raised beds would create a cold frame approach and enable plants to grow better when the weather is still cold. This framework, possibly using polypipe arches, could also be used for shadecloth to assist with heat extremes.

Here’s hoping for a better gardening season, and a sunny spring in 2023. T