Between Autumn and Winter, the soil will be softer and easier to dig due to all that lovely rain, and the rain itself will fill your pond with lovely, fresh water :)
It also means you will get your pond ready for those frogs that commence the breeding season from Spring. You might even be lucky and have other species, such as the Eastern Common Froglet, who breed all year round turn up fairly quickly!
In general, I would recommend that you build a pond that:
- is as natural as possible - if you have a clay soil, or a silt soil with clay, then consider keeping it unlined and using Sodium Bentonite Clay to help create a seal. Adding rough sand (unlimed builders sand), gravel and river rocks will complete the look;
- is no more than 30cm deep in the centre - frogs don't need it to be any deeper than this. It's generally recommended that FISH ponds are deeper because they like to retreat to the cooler depths when it's hot, but frogs can of course move out of the pond into a shaded place if necessary. It will also be safer for any children or small animals who might fall in;
- has a shallowly sloping side and / or different levels - some frogs like to sit in the water with their head above the surface and it also makes it easier to exit;
- has either 20% of it's surface shaded all day, or has full sun in the morning and is shaded at the hottest part of the day - this will help to prevent algae build up and also provide tadpoles with some protection from the heat;
- have a nearby rockpile and also some wood - this will give all the things that frogs like to eat a home and also a place for adult frogs to hide, making your pond more attractive. Dead wood allowed to rot in the pond will improve the habitat immensely;
- makes use of indigenous plants, that is those local to your area - this will encourage indigenous wildlife species to make your garden their home.
Sodium Bentonite is available as cat litter and also as a stock feed supplement, in both powdered and granular form. Ideally, you want the powdered form, but both will work.
You will need 500g to 1.5kg of Sodium Bentonite per 30cm square surface area of your pond base. The less clay content you have, the more Sodium Bentonite you need. It is not good at binding to sand, so very high levels are needed if you can't get down to a clay base.
It is simply a case of moistening your existing clay, mixing the Sodium Bentonite into the top few centimetres of this to create a bind and then layering the remaining sodium bentonite on top. The thicker this is done, the better the seal. You then compact it all down firmly before filling the pond.
This process allows the Sodium Bentonite to join with the existing clay, fill in any gaps, swell and create your seal.
Sodium Bentonite will shrink when it dries out and this will compromise the seal, however it will swell again once wet. Some people will see this as a disadvantage but, in seasonal ponds that dry out completely during the warmer months, it is a good choice.
Your pond base can then be covered by a good quality top soil, or rough sand and gravel to prevent any movement of the Sodium Bentonite when it does dry out. Then you can plant in it :)
I recommend, from personal experience, that you do not put in any sand, gravel, top soil or plants until you are sure that your seal is intact - it's a right pain having to removing everything again. Especially if it's not the first time you've had to remove it all...!
Using Sodium Bentonite allows tree roots etc to penetrate into the pond, creating a more natural environment and also allows any areas that are draining to be easily repaired with the addition of more Sodium Bentonite - even when the pond is full.
Alternatively, use a UV tolerant plastic liner that will be longer lasting and safe for use in your pond. Just be aware that this can be punctured and then needs to be removed and replaced.
It is important to let your pond be as natural as possible. Although the wildlife will not care that your pond is man-made and has a plastic liner, they do care about their surroundings.
Wildlife will appreciate mixed vegetation, with aquatic plants in the pond, marginals around the shallower edges and dense planting on at least one side. The aquatic plants and marginals provide cover and breeding sites, as well as food for tadpoles. The surrounding planting will give frogs exiting the pond cover and also a place to sing from :)
If possible, an adjoining bog-garden is an added plus and is a great way to make use of those typically contradictory Aussie soils - that are both free-draining and water-repellent!
For planting, the layer of sand and gravel will be enough of a substrate to allow plants to establish. A deeper bottom will build up over time as organic matter breaks down in the pond.
Natural also means curbing your instinct to tidy up and remove leaves etc that have fallen in, or over-handing branches.
As long as you haven't sighted a permanent pond under a deciduous tree, then some leaf litter is going to be beneficial to your pond. Excessive leaf litter can cause too many nutrients to build up in your pond, but if your pond is a seasonal one then even this will not be an issue.
A good way to have a natural pond is to site it in an area where it will fill from rain and run-off, but will also seasonally dry up over the warmer months. This will benefit the frogs that need the water only during their breeding seasons, reduce the concerns that many have regarding mosquitoes breeding in the pond, and also remove the need to use a pond pump to filter and circulate water.
In fact, many frogs require still water for breeding, so the use of a pond pump or filter actually discourages them from making your pond their home.
If you're still concerned about mosquitoes during the wetter months, and let's face it, where I live they breed all year long, then don't be. Although tadpoles will mostly feed on algae, they're not vegetarian and are partial to some wriggling mozzie larvae!
If you are concerned about cats, yours or others, then don't be. Amphibians are most often active at night, not often preyed about by cats and ensuring that you have enough cover plants for them will mean that your frog population will be little affected by the presence of our feline 'friends'. If you remain concerned, then ensure that your own cats are confined at night (as you should be doing in any case!) and consider fencing the pond area.
In my opinion however, fencing is not necessary and is just an additional expense. Please note that some councils will require ponds over a certain depth to be fenced off, and in Yarra Shire I believe that means anything deeper than 30cm.
Oh... and the big question everyone also asks is, "where do I get the frogs from?". The answer is simply that they will find you!
In Victoria, and I suspect most of Australia, frogs, tadpoles and spawn are protected. The collection of any of these from the wild is therefore illegal. The release of frogs and tadpoles into the wild is also illegal.
This means that you simply wait for your local frogs to find your pond and make it their home. Depending on where you live, frogs are likely to turn up within the first year - even in suburban areas. The key however is whether or not your pond is suitable for the type of frog who arrives and of course if they will like it enough to stay.
If you follow the info above, you will be making your pond suitable for a variety of different frogs, so the chances of you having a new froggy friend are high :)
And if they don't come? All is not lost! Your pond will be a haven for all sorts of wildlife and a valuable water source for others. There will still be plenty of enjoyment to be had.
Lastly, there are is one thing that you really need to be careful about when having a frog pond. Do NOT site it where it will get run-off from any land or garden bed that has additional nutrients or chemicals (fertiliser, foliar sprays, weed and feed, fungicides, pesticides etc etc) used on it and do not use these things near the pond. This of course goes double for any land where you might spray glyphosate.
These things are all damaging to your pond and can be deadly to the wildlife you're trying to encourage.
The best idea would be to simply stop using them ;)
There are lots of online sources of information for those building frog ponds, but some good ones can be found in the links below:
http://frogs.org.au/
These guys have all the info you need on Aussie frogs and of course have a wonderful community, so you can check out everyone else's ponds! Please ensure you check out the legal requirements for your state or territory.
http://www.amphibianark.org/
Great resources including support materials for creating a frog pond
http://www.pondconservation.org.uk/
and Dr Jeremy Biggs from Pond Conservation's blog
It would of course be remiss of me to not include SDCN's (Southern Dandenongs Community Nursery) leaflet on creating a frog habit with indigenous plants ;)
Feel free to add any others specific to your local area to the comments! :)
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