Clay Soil
Gardening in Clay Soil is often regarded as somewhat of a handicap by most gardeners, especially those gardeners that have preference for growing plants that do require a well drained soil. Most of the popular West Australian natives and South African Proteas that naturally grow in sand and well draining gravels and loams have a preference for soils with good drainage.
These plants are always very popular to grow as many have large, exotic, showy flowers. Therefore if you are a gardener with a liking for these plants it begs to ask the question…..can you still grow these types of plants in a clay soil?
Well being a gardener who has gardened in clay soil for over 10 years I can honestly say, yes, and basically it just comes down to following a few rules.
Firstly though can I just say this. Recently I was listening to a gardening program on the radio where a gardener asked the question about planting into a clay soil. The answer given by the gardening commentator was to dig down into the clay and try and break it up and maybe add some gypsum. Now this is not the first time I’ve heard this type of response to this question and in some respects this answer does bother me. Why? Well consider this.
The biggest problem with clay is the fact it doesn’t allow water to pass through it very easily. Therefore once you start digging into it you really do need to be prepared to keep digging all the way through the layer of clay until you find a layer of soil that is free draining so the excess water has a means to drain away. Now does this sound like a viable exercise for every plant you plant into clay soil? Not really, the hole you dig may have to be quite deep to make it effective.
Therefore once you start digging into clay all you’re really doing is providing an area for water to accumulate after rain. This is not an ideal situation. Now you must understand this, many areas of South Eastern Australia have been in drought up until recently so using the above mentioned method of planting hasn’t really been a problem as there hasn’t been the rainfall to make it a problem. Therefore many plants has survived for years planted into a hole dug into a clay soil.
At the end of 2009 SE Aust started getting lots of rain again and then all of a sudden plants that had survived the drought for years started to die and mainly it was caused by bad planting in unsuitable areas where excess water all of a sudden became a problem.
Therefore the number one rule when gardening with a clay soil or a clay subsoil is make sure excess water has a means to drain away. This also applies not only for water on the surface but below the surface as well. After all, if you dig a hole into a clay soil and then replace it with a freer draining soil, plus the root ball of a plant, do you really believe the excess water will drain away? No it won’t, the hole will just act like a bucket.
One solution to avoid this is to plant plants with smaller root balls such as those grown in tubes. In most cases these plants will quite often outgrow a larger plant anyway.
So what is the best solution for gardening in clay soil?
Well to start off with the obvious solution is to use plants that are tolerant of clay soils. Callistemons, Melaleucas and some Banksias, Grevilleas and Eremophilas all have some species and hybrids that are suitable.
But what if you want to plant plants that require a well draining soil into a clay soil?
Well the easy solution is to garden on sloping terrain. The excess water will easily drain away and not become a problem. Just make sure you don’t dig a large hole in the clay to your plant your plant.
But what if you haven’t got a sloping garden, what if it’s flat?
Well this is where planning your garden and good landscaping can come into play. Use raised garden beds and you can go about this in two different ways. Firstly you can import lots of suitable garden soil that is free draining or you can do what I did. I excavated an area of my garden and mounded the excess clay into raised garden beds. I then used compost and gypsum and hired a small cultivator and then mixed all the compost and gypsum into the clay mounds which were to form my garden beds. What I ended up with was a friable, well draining soil that I could plant all manner of plants that require a well drained soil.
Now if you decide to take this option just make sure the areas you excavate aren’t too deep. You can turn then into pathways and provide underground drainage to direct the water away from the garden beds.
Sound like too much work? Well remember this……….you only have to do it once.
The most important thing to remember though is you must provide a means for excess water to drain away. Correct landscaping is essential, whether it be natural or man made. At the end of the day though, there are many ways to go about gardening in a clay soil and not every plant will grow in clay but if you employ some of these basic principles you will great increase the number of plant you can successfully grow, in a clay soil.
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Banksia Oblongifolia
Banksia Oblongifolia, native to Queensland and New South Wales, is another Banksia that isn’t often seen in cultivation and home gardens. I first came across it about 10 years ago and planted it in my mother’s garden where it grew into a narrow spindly shrub about 1.5 m tall that probably only ever had about 6 flowers on it in all its life.
A few months ago I was at was at my parent’s house and noticed they’d dug it out. My mother told me it had never really been much of a plant and only had a few branches on it. So I suppose I could understand her reasoning but I was a bit disappointed as Banksia Oblongifolia was one of the few Banksia that had a lignotuber. You see I really like plants with lignotubers as they are so easy to regenerate when they get old and spindly. All you have to do is prune them back to the lignotuber and then let them grow back again and in many cases they do look better the second time around. Therefore as I said, I was disappointed that this Banksia had been dug out.
Lucky for me though, my mother quickly advised me that she’d transplanted it into a small plastic pot and here it is……….
March 11
Doesn’t really look much does it? You can see from the photo it had about 10 original branches which were all vertical and now obviously cut off. It had one remaining juvenile branch but the lignotuber and remaining branches were all covered in buds.
Being dug up after nearly 10 years in the ground and placed in a pot hadn’t really affected it at all much. Plus, from memory, it was dug up in January or February, during summer, while it was growing. So this was a tough little Banksia indeed.
Banksia Oblongifolia Lignotuber. You may be able to see the new buds forming.
Therefore for the last few months it’s been growing quite happily in this pot.
By April 26 it had quite a nice canopy.
By May 15 it had thickened up even more.
So now I’m just waiting for it flower. Winter is it’s normal season but I don’t think there will be any flowers this winter so I’ll just have to wait till next year. So as you can see, you don’t have to dig out old Australian natives and throw them away. You can either prune them back according to how they grow or you can simply transplant them, as with this Banksia.
At the end of the day I think Banksia Oblongifolia looks ok just growing in a pot. I could either prune it back to expose the lignotuber more (like a bonsai) to make it a feature or I could just let it grow and wait for it to flower.
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Banksia Ericifolia
There are several varieties and subspecies of Banksia Ericifolia that are available in nurseries today. Some are more garden worthy than others. In my last garden I grew two different varieties. The first was a variety called “Little Eric”. This was a great little Banksia that only grows to about 1.5 m in height with a spreading habit.
Banksia Little Eric
The best thing about this Banksia is that I grew it is a shady area under a large tree that was growing in the house next door. The roots from this tree ensured that the ground was always bone dry and despite this it always puts on a flowering display every winter and never shows any signs of stress. So if you’re after a plant to put in a dry shady area this might be a very good choice.
The other type of Banksia Ericifolia I grew was the more common subsp Ericifolia which was quite a nice looking plant but the flowers were well hidden inside the foliage and as a consequence they were hard to see. I do believe that there is a variety though where the flowers are longer, more terminal and protrude above the top of the foliage more so they are more visable. So a word of warning, choose wisely at the nursery if you want a plant that will put on a show when in flower.
There are also a few hybrids as well that are worth a mention. Banksia “Giant Candles” is the most well known. A hybrid with B Spinulosa this Banksia gets its name from the long flowers it produces, up to 40 cm long. The shrub itself grows up to 5 or 6m and could nearly be classified as a small tree. I grew this in my last garden. It tends to grow reasonably fast and is covered in long orange flowers over winter.
Banksia Giant Candles
Another Hybrid is called Banksia “Yellow Wing” a hybrid between Giant Candles and B Spinulosa (Canarvon) “Birdwise”. I’m currently growing this one in my garden at the moment but the growth has been slow. I’m not sure if this is due to the phosphorus in my soil or just the dry conditions. I might try giving it some more water and we’ll see if it grows any faster. The other thing is that apart from the slow growth it hasn’t shown any signs of phosphorus toxicity whatsoever so it appears to be resistant to the effects of the phosphorus.
Banksia Yellow Wing, surviving the Phosphorus
Banksia Ericifolia grows naturally on the east coast of Australia and typically has long orange, burgundy or yellow candle like flowers that occur over winter and into spring. It normally grows to 3m but this is variable in the different varieties. Despite coming from an area that gets up to 1000mm of rain per year it is still very drought tolerant, adaptable and easy grow in the home garden.
Banksia Ericifolia “Little Eric” and Banksia “Giant Candles” are the ones that I’ve had the most success with and would recommend them as starters but I’d be very interested to get some feedback on what other people have tried.
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