The poem ‘My Country’ by Dorothea McKellar and its lines about “A land of sweeping plains, Of rugged mountain ranges, Of drought and flooding rains” springs to mind (pardon the Dad joke) as I reflect on my last newsletter. I talked about how to use water efficiently, with a nod to our all too often dry country. If only Dorothea had known about the ‘La Nina’ phenomenon when she was writing her poem I am sure it would have inspired another great verse. For those who may not know about it, weather scientists tell us we are in a period where high rainfall events are likely over the next few months across the Australian east coast.
So when I spoke about efficient water use in the last newsletter it was somewhat bemusing to subsequently have a number of very wet spells here on the farm just as I was expanding my arboretum plantings. I had deep ripped lines for my tree and shrub seedlings to ensure that not only did the root systems have relatively loose soil to grow into, but also that every precious drop of rain would be channelled down to their roots over the long term, ensuring that their root systems grow down into the subsoil moisture as I don’t intend to run irrigation lines to them. With the very wet winter the water table underneath the plants has risen in several places resulting in the trenches temporarily filling to the brim with water.
I have lost a handful of Western Australian Flowering Gums (Corymbia ficifolia) in a couple of unexpectedly very wet spots up on a ridge, but in other spots in low lying areas that I knew would be wet when it rained, I chose species that I knew would handle periodic inundation such as Melaleucas (paper barks) and Leptospermums (tea trees). Overwhelmingly, all the trees that have established themselves successfully are responding to the extra water which is helping to release the nutrients from the handful of Bush Tucker fertiliser that I had thoroughly mixed into the soil in each hole.
This helps demonstrate my two ways to deal with the problem of having too much water when growing plants (or indeed other environmental problem issues). You can either select plants that suit the environment, or change the environment to suit the plants.
Water logging of soils temporarily creates anaerobic conditions (i.e. conditions where there is a lack of free oxygen) which can encourage a tilt in the balance of soil organisms such that anaerobic organisms such as some that cause root and crown rots proliferate, encouraging disease, and causing or exacerbating nutritional imbalances, and in the worst case scenario, plant death. Most plant species thrive in soils that have plenty of air spaces to allow good air exchange (and therefore oxygen) for plant roots and the microbes in the soil directly around the roots (also known as the rhizosphere). Soil that holds copious amounts of stagnant water for any extended period of time will not, and in such conditions the majority of plant species that are not adapted to anaerobic soil conditions will suffer. Apart from the obvious pools of water on the surface, anaerobic conditions are often accompanied by nasty smells such as that caused by rotten egg gas (hydrogen sulphide) and methane.
Excluding oxygen from the root zone can often be overlooked as the cause of the decline of plants….as the roots start to die off it leaves a plant less able to uptake the needed moisture and nutrients for proper growth. One of the seemingly paradoxical symptoms of too much water can be wilting, whereupon the gardener pours more water on, which can sometimes seal the fate of the poor plant. Same too with a nutritional deficiency, where more fertiliser is applied, but with a compromised root system, it is wasted and no improvement is seen, and often it can cause even more damage to a struggling root system.
So what can be the cause of waterlogging? In the garden it is usually low lying areas that can be boggy, as water heads downwards. However, as I have discovered on the farm, the underlying geology can also result in springs in higher areas, sometimes known as ‘perched’ water tables. In any event the cause of extended waterlogging is usually the result of poor drainage through the soil profile (sometimes coupled with an impenetrable rock barrier that stops drainage completely). Heavy clay subsoils are another likely cause of extended waterlogging.
People with sloping property can feel like they would have no problems, but it can be overlooked that water may be draining from neighbouring higher up properties, particularly if recent earthworks have changed the surface and sub-surface movement of water. Potted plants can also be hiding a stagnant water problem, not only from a dense root mass and very little soil volume (and thus not much air space), but also from blocked drainage holes or being placed in a saucer that is never allowed to dry out.
!. Some ways to improve a waterlogged area by modifying the soil environment to suit the type of plants you want to grow:
- Install sub-surface drainage systems in your garden using ag-pipe (slotted flexible pipe that allows water to enter along its entire length), rubble drains, etc. Do it yourself products are available but I recommend you consult a plumber or landscape professional OR read up on the best method to install as you don’t want to pass your drainage problem on to your neighbour (indeed this may be illegal) or give yourself a different problem with wrongly installed products. Drainage systems will only work if there is somewhere for the excess water to go, however. If you are in a dead flat area, there are some innovative solutions such as the ‘Soakwell‘ that will create a sump in your soil that allows that water somewhere to go that will not harm your plants.
- Compost, compost, compost! Soil with a high organic content will help create better soil structure with a wider range of pore space sizes that will help to allow excess moisture to percolate through, but will also absorb water like a sponge that can later be utilised by the plant. This may sound conflicting, but that is the beauty of composted organic material. Not only can it help sandy soils that don’t retain enough water, it can also help those that have poor drainage, truly a miracle material that anyone with time, energy and access to organic matter can create simply. Use anything you can get your hands on to use in your compost or worm farm…… fallen leaves, grass clippings, prunings chopped small, kitchen scraps, coffee grounds, shredded paper, ripped up brown corrugated cardboard (I leave coloured or shiny cardboard out of my compost though)
- Raised beds can create what will effectively function like very large pots that will grow a very wide range of plant species. With these, you can much more easily control the amount of moisture going to the soil. Raising the root zone of your plants allows for better drainage in very wet periods. The only downfall of a raised bed is that extra irrigation will be required in dry periods, which is why I like the technology of wicking beds which allow the storage of water at the bottom of the bed, but also allows for drainage in times of abundant rainfall.
- If you have dug a hole into heavy clay soils to plant into, this can trap water for extended periods in wet weather. To get the best result possible, either use my method of deep ripping the soil (as far down as you can go to break up the subsoil to improve drainage) or, if you are in a garden situation, use a mattock or pick to dig as deep a planting hole as possible and to break up the subsoil to improve drainage
- If your potted plants are often wilting or look unthrifty as time goes on, they may need repotting into fresh soil and a larger pot. One of the best ways to diagnose waterlogged pots is to sniff the bottom of the pot for nasty smelling gasses created by microbes that live in waterlogged conditions. Or knock the plant out of the pot and inspect the bottom and see if the roots look rotten.
What to do if you can’t change your water issues-
Some plants have evolved to survive or even thrive in boggy conditions, so if you can’t afford to or don’t want to change your waterlogged conditions, search out those plants that will revel in the sogginess. Clumping plants like rushes and sedges (Juncus, Carex, Ficinia, Baloskion) can be very ornamental if used creatively, as well as creating habitat for wildlife and potentially filtering grey water (another subject for an entire newsletter). Bottlebrushes (Callistemon), paperbarks (Melaleuca) and tea trees (Leptospermum) are among the native plants that thrive in boggy conditions as well as the well named swamp lily (Crinum pedunculatum). Good nurseries will be able to point you to the right plants for your needs, we have partnered with some terrific ones on the Gardening With Angus website nursery directory>>>>